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Author Topic: OPS 60 engine  (Read 10264 times)

Ramon

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OPS 60 engine
« on: June 14, 2009, 12:23:14 AM »

Hi,

Sometime in the early seventies I bought an OPS 60 WCRCB engine from HJ Nichols in London. For the time this was one chunky, extremely well made and outstanding engine with a performance to match. A significant improvement over the Merco 61 then in use!
Unfortunately I lost the pipe overboard due to minimalist fixing and with my work taking me overseas shortly after, to my eternal regret, I sold the engine and boat on.

Fast track some thirty odd years and as mentioned on the ‘1/8 scale Huntsman’ thread another version of this engine came my way and is currently fitted to a secondary project of which perhaps more later. This version has an air-cooled head (came with a ‘Kool Klamp’ fitted). When received it was in a bit of a sorry state so it was stripped down, cleaned and rebuilt. Stripping revealed a bent con-rod and though it was difficult to remove this as per normal methods, no further damage occured and remarkably very little wear was evident. After straightening the rod however, the engine assembled well and is now in fine, though as yet un-run, order.

Recently I purchased ‘unseen’ another example. I bought it, well aware that it was ‘seized’ following a dunking in salt water but thought it might be useful for spares. It’s condition when it arrived a couple of days ago matched expectation but upon careful examination it looked as if this too could be rebuilt.

I thought it might be of interest to see what transpires.







Looking at it, one ‘positive’ is that it had seized with the piston well up in the bore so theoretically the top end of the liner may possibly be unscathed but first those screws  would have to come out. As expected, not many would but the exhaust came off easily enough - good start - followed by the back plate but nothing else would so much as shift so it’s into a container of Plus Gas to leave for a good soak for a day or so. (I never realised until quite recently that this penetrating fluid was still available)





Hopefully the fluid and maybe a bit of heat in the right areas may just get to grips with the rest.

Hoping this may prove of interest to someone
Regards - Ramon
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bogstandard

  • Guest
Re: OPS 60 engine
« Reply #1 on: June 14, 2009, 05:55:09 AM »

Ramon,

I used to run the '40' sized one of this engine in the early to mid 70's. A pure powerhouse compared to what was available at the time. It was a choice of either the OPS or the very expensive Webra.

The main failing point of what I can remember was the carb and how it was fitted to the rear induction manifold, the dreaded clamping pin setup. The whole lot would fall apart at the slightest opportunity, you were constantly 'aralditing' it all together to stop the carb falling off. Also, it was a constant battle replacing broken needle stems (vibration used to cause the bent wire adjusting handle to snap off). This was later cured by fitting a big bore third party carb. But then starting problems ensued, an electric starter with a larger pulley was a must, to get it up to a speed that it would start and 'tickover' at.

Coupled to a Weston fibreglass water cooled tuned pipe and an SHG shark hull, anti vibe mounts and a flexishaft (all new ideas in those days), it was a force to be reckoned with. The original 'quiet' pipes were just too fragile to be considered, they were made of such thin aluminium, they dented if you looked at them for too long. Those were the days when the 80DB noise rulings were being considered and introduced, and a time when a lot of good sailing water was lost due to people not sticking to the rules. Fast electrics were a specialist field with boats actually crammed to sinking weight with batteries, and it was in that field that things progressed more rapidly, trying to gain back all the lost sailing venues in local areas.

They really were the 'bees knees' in those early days, and I wish you well in the rescue of a couple of good examples.

Bogs
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Ramon

  • Guest
Re: OPS 60 engine
« Reply #2 on: June 15, 2009, 11:45:58 PM »

Hi,
Interesting memories Bogs, I don’t recall problems with the carb on the 60 but then it wasn’t raced, well that is, pushed to the limit, and it was always hand started with a cord!! I think I also ran it on straight mix i.e. no nitro which if memory serves correct was how the OPS of the time was set up. Ah! too long ago to think about eh? ok2

That ‘thin’ pipe I do remember and seeing it disappear – for the second time – (didn’t learn much there the first time) was a gut wrencher. The first was very close to the bank and was retrieved but no such luck the next time. One thing’s for sure they will be held much more secure this time round!! %)

Well despite it’s appearance and condition and after a few anxious, ‘nipped up’ moments I’m pleased to say that the engine is now stripped to it’s major parts.



Three of the head bolts lived up to expectation, the first undoing with that ‘crack’ of a well torqued caphead. The force required on the others was immense but the normal worry that the socket would open or the key would ring was not founded. It was only after I picked up the hex key to take off the front housing that I noticed the inbuilt corkscrew!!  :D :D (Sorry just couldn't resist these!!)


With the head off, the next concern -  the flywheel – proved unfounded. It fell off with a single tap with a plastic faced hammer. The real sting in the tail though was the liner - an absolute sod but lots of heat, some ice cold water poured in the liner at the moment of truth courtesy of SWMBO and out she popped unscathed.

The piston was extremely tight in the top half of the liner (interference fit 10mm from the top!!) and it turns out this was due to a virtually invisible ‘salt(?)induced glaze’, the bottom half of the piston some 2 thou bigger than the top half. Thoughts of how to true the piston diminished after dunking the piston in cellulose thinner revealed the glass hard glaze as a white deposit. A very careful scraping with a scalpel showed the deposit had broken down in the thinners and it just flaked off. A very light touch with a piece of 1200 wet and dry with lots of lube and the piston dropped back in the liner running smooth and just nipping at the top as it should. So far so good.

The main bearing had totally seized and the crankshaft shows sign of running in the bearing. The bearings were much easier to remove than expected and some replacements are on order at a local supplier.


Since this pic the gudgeon pin has been removed as the con-rod needs rebushing at the bottom end, the little end showing no sign of wear.

Does anyone know of a source of the circular wire retaining clips that retain the pin or are these specific to OPS engines.?

Well that’s it, stage one over much more quickly than anticipated. The rebuild will be much more sedate as I would like to bring it back to as new a looking condition as possible – I’m promised the use of a bead blaster to clean up the castings but that won’t be until next week.

Back soon after that then   
Regards - Ramon
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bogstandard

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Re: OPS 60 engine
« Reply #3 on: June 16, 2009, 09:14:17 AM »

Ramon,

Mine ran on 5% nitro, and we used to mix our own blend.

With regards to the pin spring retainers, you can obtain very small internal circlips that should do the job, maybe more efficiently than the original idea. Or maybe grind some ring sections out of a spring of the right size. They are taking no massive forces, just acting as float end stops for the gudgeon pin.

If not, I would write a nice email to customer services at OPS (if you can get past all the middle men importers and retailers), I find most big companies are very sympathetic to one man band pleas for help. They can only say one of two things, and this time you just might be lucky. Pile it on about reliving the past, and how good an engine it was, and is such a shame it would have to be junked if the spares weren't available etc. Attach a pic of the stripdown, just to show you are bona fide.

Bogs
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ids987

  • Guest
Re: OPS 60 engine
« Reply #4 on: June 17, 2009, 05:00:55 PM »

Hi Ramon,

I am pretty certain that's not a OPS .60. It appears to me, to be either a .67 or a .80.
The good news is they still make both (unlike the .60s) - although they fairly recently stopped making the disk rotor / bushed rod versions.
All of the "current" .67 and .80 engines have steel / needle roller rods, and drum valve induction.
Visually, it is hard to tell the difference between the .67 and the .80. I think they both have 23mm stroke. The .67 has ~24.6mm bore. The .80 has 27mm bore.
It would also seem that the "new" "bimetal" OPS .90 is a development of this same engine. Same crankcase, but anodised black, and featuring the same 23mm stroke. Advances in the last 20+ years, seem to include (but are not necessarily limited to): Fancy anodising of crankcase, flywheel, and head. Billet front bearing housing and drum rotor housing (a genuine improvement - though Aeromarine used to offer similar aftermarket parts). Ability to overbore the liner again (.65 -> .67 -> .80 -> .90). Some balancing and porting work.
Mantua Model are the UK distributor for OPS engines, and may be able to help with parts. Clips for a Picco .67 should fit if you can get them. I think CMB .67 wrist pin size is either the same, or very close, so CMB .67 circlips would probably work ok (and should be easiest to get).
Some info on the new OPS .90 is here: http://ne-stuff.blogspot.com/2009/03/new-ops-90.html

Ian

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andyn

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Re: OPS 60 engine
« Reply #5 on: June 17, 2009, 05:19:16 PM »

Ian is right, this is the OPS .67

It is drum valved, but does have a double bushed con rod. Note the new milled backplate.

https://www.mantuamodel.co.uk/prod.asp?product_idx=525&imgstate=0

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ids987

  • Guest
Re: OPS 60 engine
« Reply #6 on: June 17, 2009, 05:47:26 PM »

Ian is right, this is the OPS .67

It is drum valved, but does have a double bushed con rod. Note the new milled backplate.

https://www.mantuamodel.co.uk/prod.asp?product_idx=525&imgstate=0



I thought that the drum valve engines were needle roller, and the disk rotor engines had bushed rods - they offered them side by side for some time, but I guess it's possible that both were separate options. I also thought that all the current .67+ sizes were needle roller rods. I could be wrong, or Mantua may have got it wrong - wouldn't be the first time on either count. According to Mantua, the new 20cc is also a double bushed rod. I find that kind of hard to believe - though if that one is also the same old crankcase, they may not have had room for needle rollers. The crank pins on the needle roller .67s and .80s were too small for comfort really.
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Ramon

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Re: OPS 60 engine
« Reply #7 on: June 17, 2009, 05:51:40 PM »

Hi Guy's

have just seen this but have to go out soon but will respond later

I shall be drooling all evening Andy

Ramon
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andyn

  • Guest
Re: OPS 60 engine
« Reply #8 on: June 17, 2009, 05:54:52 PM »

From Mantua's website.

Quote
OPS MARINE 11cc-.67 op82711 engine. This is the new drum valve version and is very popular either for competition or sport, this engine is very rugged with lots of power at both ends and comes with slide carburetor with bell crank for easy installation and a double bushed con-rod fro long life.The engine comes with a marine tuned pipe.

Although, a quick looks at the parts list on Niagara Hobbies shows

Quote
OPS6520 Needle Rod
Quote
OPS6750 Needles for Rod

So I think Mantua have it wrong.
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ids987

  • Guest
Re: OPS 60 engine
« Reply #9 on: June 17, 2009, 06:31:24 PM »

From Mantua's website.

Quote
OPS MARINE 11cc-.67 op82711 engine. This is the new drum valve version and is very popular either for competition or sport, this engine is very rugged with lots of power at both ends and comes with slide carburetor with bell crank for easy installation and a double bushed con-rod fro long life.The engine comes with a marine tuned pipe.

Although, a quick looks at the parts list on Niagara Hobbies shows

Quote
OPS6520 Needle Rod
Quote
OPS6750 Needles for Rod

I found the listings on Niagara's website as well. They still list four .67 and .80 models (whole engines), but these now come down to .67 DRV with needles, .67 DRV with double bushed rod, .80 DRV with needles, and .80 DRV with double bushed rod. If that is correct, then OPS have just replaced the disk plus bushed rod versions with drum plus bushed rod versions. Hard to get hard info on OPS engines - since there isn't a "OPS engines" website. Ironically though - to the best of my knowledge, Mantua Italy (the parent company), own OPS.......

Ian

So I think Mantua have it wrong.
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andyn

  • Guest
Re: OPS 60 engine
« Reply #10 on: June 17, 2009, 06:58:30 PM »

So they obviously do both, and like a couple of other retailers they don't show everything... Probably a case of right hand not knowing what left is doing...

Another problem solved by the Stevenage modelling duo ;)
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ids987

  • Guest
Re: OPS 60 engine
« Reply #11 on: June 17, 2009, 07:26:31 PM »

Or they're "new old stock", and Mantua are just advertising what they have left.
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ids987

  • Guest
Re: OPS 60 engine
« Reply #12 on: June 18, 2009, 02:34:35 PM »

Must admit, the opening couple of posts in this thread brought back a flood of nostalgia.

I remember going - in about 1983, to Aeronautical models in Camden Town - not much more than a stones throw from what was HJ Nicholls - now 308 Hobbies.
I'd just joined BT as an apprentice, and having thoroughly researched the Ripmax catalogue, I went - armed with most of my first week's wages, and most of the money I had just got for my birthday. Having compared the HP and RPM stat's in the Ripmax book - all referred to the Merco 35 I had at the time, I had decided to buy either a HP or Webra engine. I left the final casting vote to the shop assistant - Which is the most powerful ? When he said the OPS 40 was much more powerful than either, I made my mind up there and then. Got it home still reading the spec sheets - 26,000 RPM. That's double the RPM of the Merco, and about four times the Horse Power. Much more RPM, and about double the horse power of the Webra or HP. Wow !
Of course it wasn't four times as fast as the Merco - which disappointed me slightly, but it was definitely fast, and the compression - plus the tightness of the brand new engine, made starting it with the leather thong a bit of a challenge - especially when it was saturated with fuel. Still, I persevered (a little), and gave it the short run in period specified in the instructions. I also had all the fun of carb pinch bolts coming loose, eventually broken needle valves, but through it all, great engines. All part of the fun - like the blisters from the starting cord.
My interest lasted a couple of weeks. Then renewed a few years later. The OPS 40 came out of it's original SHG Contester (multi boat) - after a "boat meets wall" incident, and found a new home in a Racing Models multi boat. Again, my interest didn't last long until it went away again - to resurface after house moves etc, in 2004 - when I joined the boat club at Stevenage. My first couple of purchases (eBay), were a Webra 61 and a OPS 60. This time around, the interest has remained a bit longer - must be a sign of old age maturity.
I now have "a few" OPS engines and bits thereof in the .21, .40, .45 and .60 sizes. I had a .90 for a while, but I've never owned any of the .65 / .67 / .80 family.

Keep up the good work Ramos - bring it back to life.

Ian
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nemesis

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Re: OPS 60 engine
« Reply #13 on: June 18, 2009, 09:53:52 PM »

Ahhhh, Memories, nostalgia, all those multi races. thank you. Gudgeon pin circlips, visit your local
orthodontist for some stainless steel wire.
                                              Nemesis
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Ramon

  • Guest
Re: OPS 60 engine
« Reply #14 on: June 18, 2009, 10:50:58 PM »

Hi guy's

Thank you all for your input. :-))

The spring question seems reasonably resolved and I shall explore the avenues suggested beginning with the spring idea but I fear the helix may prove difficult to remove however I shall try.

The '67' was a pleasant surprise - though I owned an OPS 60 before it had a plain ally head and a water jacket. I have seen there are variations and bought this as a '60' so accepted it as such.

The bore though is definitely 24.6 which seems to coroborate Ians comment. The conrod that was bent in the 60 previously worked on was a forging but this one is machined with both ends bushed. It has some wear on the big end which will be easy enough to rebush but the pin is very slightly oval which won't and as mentioned the crank is down on the bearing ID though some (very) judicious use of bearing fit should prevent the shaft running in the bearing. We are only talking a couple of tenths though.

The disc has been modified, 'flowed' at point of cut off and the rim opposite the inlet opening relieved I guess as an attempt at balancing but the running fit and the face to face contact is good. This brings me to a question.

I am very familiar with rear intake glow (and diesel) engines but no idea what a drum valve looks like or the difference between it and a disc. Could someone explain this for me - pic would be appreciated. I'm visualising the inlet port on the periphery of a hollow disc. Is there any advantage?

The cylinder bolts (3.5mm x .6 x 30) are not to bad considering the force required to get them out but I decided I would replace them. What a run around - two local major 'fastener' companies "sorry we dont even list them" - Ripmax, really nice guy, suck of the teeth "you'll be lucky" - internet??????? no luck. Then by chance saw 'Model Fixings'

http://www.modelfixings.co.uk/high_tensile_steel_caps.htm

Absolutely brilliant site, have all sorts of goodies, ordered 4pm Tuesday, came this morning so that's one efficient service and a problem solved.

Now all I have to do is bring it up to match yours Andy and I shall be well pleased. The special backplate - is that a home improvement, aftermarket part or yet another OPS version?

Ooh you're getting into it now Ian. Just 'little' earlier (71ish) I got into boats by chance and after the ubiquitous aerokits  PT boat and Swordsman took an interest in the timed Naviga 'Triangle' event - 30 meters a side, round once and then back again and just against the clock - no other boats. I bought a fibre glass hull from Michaels Models in Finchley who used to do all sorts of 'racing bits' for boats and aircraft. It was made by ED, evidently the same company who made the diesel engines! and was called 'Sea Queen' slightly different I should add from the Aerokits 'Queen'. Very shallow vee with spray rails I set out with  Merco 61 in it and could just about control it accurately. Then I read about OPS and just had to have one. Swmbo was really impressed!! Oh it really lived up to it's reputation - trouble was the boat was so fast my reactions at the bouys just couldn't cope and and it would go all over the place either over or understeered. It didn't half get a move on in a straight line though and that's how I ended up using it till the pipe took a dive over the side.

The Huntsman I'm currently building is just to get my hand back in but what I'm really looking to is going to be something much faster and hopefully this engine will repeat the last ones performance.

My thanks again for all for your input, it is valued. I shall keep you posted on the development.

Regards - Ramon
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ids987

  • Guest
Re: OPS 60 engine
« Reply #15 on: June 19, 2009, 11:44:44 AM »

Hi Ramon,

Drum rotors come in two main flavours. In one type, the drum and backplate assembly is functionally very similar to crankshaft and front end assembly of a front induction engine. If you imagine transplanting this onto the back of an engine like the OPS. Then imagine that the crankpin from the front induction engine has been cut off, and the crank has been slotted (or bored) - so that this becomes a "slave" - driven in the same way as the disk rotor in your engine. This is the kind of arrangement used by CMB for the .21 Valvola, and the "HR" versions of their .45 and .91 engines.
The photo posted by Andy (and that nice shiny backplate), is a OPS drum rotor engine. It works in almost exactly the opposite way to the arrangement described above. The drum is still hollow, but the carb is in the middle instead of the outside. In this arrangement, the end of the drum facing the carb is open, and the end of the drum facing the crankcase is closed. The drum has a similar window to the example above, but in this case, it is used to let gases out into the crankcase - through a window in the top of the backplate. This kind of arrangement is also used in the Picco drum rotor engines - as well as the "HR" versions of the CMB 67 and 80.

I've tried to upload some images below - backplates minus drums. Hopefully they will speak a thousand words.

Michaels Models. Another blast from the past...........



 CMB 91HR / Valvola type

 CMB 91HR / Valvola type

 OPS / Picco / CMB 67 type
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ids987

  • Guest
Re: OPS 60 engine
« Reply #16 on: June 19, 2009, 05:56:38 PM »

With regards to advantages, drum rotors are generally more reliable than disks - or at least than the kind of disks used by OPS and various others (any comments herein are referring to disks generally like yours Ramon - not Zimmerman disks). I believe that drums probably - on the whole, seal better as well.
Disk rotors need fairly regular maintenance - to keep the clearance as it should be (somewhere around 3 thou as a ballpark). They are prone to slackening off - as well as slackening of the pin retaining mechanism, shearing of the pin itself etc, and it is not unknown for a pin to find its way somewhat further into an engine than it should. It is also not unknown for a disk to disentegrate / shatter. I have heard that the OPS 40s were quite prone to this at high RPM - giving a nice sandblasting to the whole insides of the engine. The OPS 67s (and even the old 60s) though, had a sleeve / bush arrangement in the centre. This should help - by reducing the tendency for the disk to "chatter". Plus they don't rev as high as the 40s. Maintenance of disk rotor engines often includes trueing the face of the backplate. This is less likely to be needed if the rotor gap never becomes excessive.
Advantages of disk rotor engines (over drum) are generally: Greater induction port area. Straighter / less obstructed gasflow path. Better packing and crankcase pumping (at least better than the "type 1" drum - where the charge enters through the periphery of the drum, and exits through the centre of the drum) - due to less crankcase volume. Though the case volume of the "type 2" drum is about the same as a disk rotor engine. By all accounts, disk rotors also (generally) have less parasitic drag than drums.
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Ramon

  • Guest
Re: OPS 60 engine
« Reply #17 on: June 19, 2009, 10:54:11 PM »


Ian that really is helpful. Thanks a lot for taking the time to expain it so clearly.
I didn't notice it before but I visited the link you posted on the new 90 and can see exactly what you mean. OPS engines never fail to impress me with their absolutely beautiful machining quality.

I did not really run my original for very long ie elapsed time so it never really got a great deal of use. Life suddenly took a 180 degree turn and it wasn't that important at the time (It b---dy well is now though!) but whoever it was that bought it certainly got a good buy. Hopefully this time that will change but given the spares situation on the 60's I shall certainly try to be a bit conservative well at least to start with %).

You may have noticed the thread on the Huntsman -  this is intended just to get my hand in. Just before things went pear shaped I was really intent on building a hydroplane and that is the road I intend to take. The OPS 60 sits in one currently being built and hopefully this 67 will see something similar - eventually.

Thank you and all the others for your help and input - this really is a great way to share and help others.
Kind regards - Ramon
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Ramon

  • Guest
Re: OPS 60 engine
« Reply #18 on: August 21, 2009, 11:17:04 PM »

Hi there again

Well at last it's back together and hopefully ready to run %).

When I first took this out of it's package my initial thoughts were that it was beyond all hope {:-{. However I really am surprised at the outcome but obviously extremely pleased.

Having said that it didn't actually take a vast amount of work though the 'set ups' needed care.
When the new bearings arrived they just 'fell' in so the housings were bored oversize, sleeved and rebored. This and the big end which had to be bored out and rebushed was the only essential machining, the other - a new 'button' and the watercooled head were done purely for aesthetic reasons. The internal water way is split ie in one side - runs around the front - out again the other. It was decided not to cut the fins (at this stage) - if it proves neccesary the finning can be done at a later date.

The carb is from a Super Tigre 60 the intake bored to 9.5 dia (about the max that could be safely removed) and a couple of extra grub screws put in the housing to hopefully offset any tendancy to shake loose. If anyone has an original carb and could measure the bore diameter it would be nice to know what it should be.

Compression wise - well despite the scraping off of the salt deposits it seems 'reasonable' - not totally brilliant but certainly better than had been expected and those wire spring clips? £1.38 for two at Mantua models - OPS agents! well where else?  :embarrassed:

Anyway - a few pics -

Parts ready for re-assembly - yes it will get a new shiny glo plug


Backplate lapped - those 'micro scratches' came off the first fitting of the disc -aaagh!




Ready to run?



What's it going in? well at this stage it's destined to go in the hydro once that is up and running and basically trimmed but that's a while off yet.

My thanks to all who responded to this post. I would just like to say that I'm not unaware that for many to do similar may be impossible due to lack of kit or knowledge of machining. In all probability this may be of minimal interest however I hope it will be of use or interest to some one - the information, knowledge and online friendship it has garnered for me has been truly enlightening.

Regards to you all - Ramon.
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gwa84

  • Guest
Re: OPS 60 engine
« Reply #19 on: August 23, 2009, 12:44:08 AM »

excellent job bud one thing i love is watching an engine of eny type being restored to its former glory and put back to good use nothing saddens me more then seeing one rotting away somewhere  :-))
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Ramon

  • Guest
Re: OPS 60 engine
« Reply #20 on: August 23, 2009, 09:39:09 PM »

Glad some one got something out of it GW. Thanks for your kind comments.

When you consider the workmanship that goes into the make up of any engine let alone the fine machining of the 'racing  types' it is such a shame to see them in a distressed state. I have always enjoyed owning 'engines', though definitely do not 'collect' them, but must admit I would rather see them looking in top condition at the expense of outright performance. I once bought a M'cCoy still in it's tatty airframe and well cowled. I dont know how long it had been in there but the cylinder fins were actually solid with baked on carbon - I don't think the cowl had ever been off!

Next one to rebuild is an OS 77 but that needs a new piston. I've made them before but never for an engine of that calibre so ''we'll have to see'............?

Regards - Ramon
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ids987

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Re: OPS 60 engine
« Reply #21 on: August 24, 2009, 03:59:43 PM »

More nice work Ramon - scrubbed up very nicely.
From memory, I think the old OPS 60 carbs were about 9mm bore. Not sure if the 67s are / were the same.
The bearing housings were a weak point in all the old OPS engines. Some (probably RPM) used to make aftermarket bearing housings from billet. I think OPS themselves use billet now.
Is the fit of the middle section of the crankshaft in the housing ok ?

Ian
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Ramon

  • Guest
Re: OPS 60 engine
« Reply #22 on: August 24, 2009, 10:34:13 PM »

Hi Ian, thanks again. looks like the 9.5mm will be a good starting point. Don't know how the ST carb will perform but they used to do quite well on STG21/46s Can only wait and see.

Interesting to hear the fact that the front bearing housing did not live up to expectation enough to warrant someone producing an aftermarket part.

On this one the mid section appeared 'half' ok - the main bearing end was a good running fit on the shaft and not affected by the immersion - I guess due to a good layer of castor. At slightly less than half the length the outer part toward the front bearing was slightly larger and though somewhat corroded 'appeared' unmachined.  I used the good part to mount the housing on a mandrel then bored the front bearing recess and trued up this corroded bit to the recess with a very light cut. This was mounted on another mandrel to bore the main housing. It all aligned okay without binding and I would imagine the length of the running fit more than long enough to maintain crankcase pressure. Failing that it looks like a new front housing could be on the cards.

Regards for now - Ramon

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