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[logoman]

Hi,
Everytime i run my Hemmens Caton V4 (on the bench) the engine locks after about 5 minues.
I have fixed i a couple of times my tightening the screw pins that connect the piston rod to the connecting rod.
These screws seem to always catch on the cross-head guide.
I dont know how to fix this problem, it's a complicated engine and I don't think I could dissamble/reassemble.
Perhaps some sort of loctite on these pins? Anyone else have this engine?

[southsteyne2]

Hi sounds like something loose here as you say runs for about 5 min ,I would advise to mount the engine on a bench or such and run on compressed air then observe closely what is taking place , could be wear how old is the engine? if everything goes fine here it could be heat related.
Cheers
john

[logoman]

Thanks for the help John, I ran on air and found that it ran well in one direction without issue, but in the other direction it locks after a minute or two. I'm sure it is one (or more) of the pins that conect the piston to the con rod working loose. The engine is in almost new condition.

I thought of using a threadlock on it, but since everything is covered in oil i doubt it would work.

[Laker]

Hello Logoman,
I don't have one of these but I do build and run steam engines myself.  From what you have described I suggest that the problem is unlikely to be related to heat/ thermal expansion of parts if the same thing happens when running on cold compressed air as when running on steam.  Your suggestion of cross-head screw pins coming loose could be right - are you able to check whether they are loose after you have run it?  If that turns out to be right you may still be able to fix it with the right grade of Loctite - I think it can still get a hold even when surfaces are slightly oily, although you should try to dry the parts as much as possible before applying it.  The only other suggestion I can make is not to force anything on an engine like this!  Much better to be patient and find the real cause than try to press on and risk damaging some parts.  Good luck with it,
Laker

[logoman]

Thanks Laker!
there was a pin loose when i checked it, and so far the only explanation is that the when this pin comes loose and proud of the surface it is driven under the force of the engine into the cross head guide (which on this engine is like a slotted tube) and locks there. When the engine cools I need to apply some force (horrible to do, but cant think of any other solution) to turn the flywheel and thus release the cross head back out of the guide - turning the engine over by hand then seems to show that it is the pin hitting the end of the slot in the cross head guide - tightening the pin allows the engine to turn freely. I cant figure out why the pin should work loose only when the engine is running in one direction and not the other.

Which Loctite do you recommend?

[Laker]

Logoman,
Have a look at Loctite 243 - I have copied in some description here:

"Loctite 243 - Medium Strength Oil Tolerant Threadlocker 10ml
LOCTITE 243 is a general purpose threadlocker of medium bond strength. This threadlocker secures and seal bolts, nuts and studs to prevent loosening due to vibration. The product works on all metals, including passive substrates such as stainless steel, aluminium and plated surfaces. It is proven to be tolerant of minor contamination due to industrial oils, e.g. engine oils, corrosion prevention oils and cutting fluids.   Threadlocking Adhesive - medium strength. General purpose. Suitable for all metal threaded assemblies"

If I remember correctly this is the type I have in my garage.  It is a blue liquid and the medium strength formula means that you can be reasonably sure that the thread can be undone again in future if you really need to.  With the high strength ones you may never get the thread undone again.

Hope this helps,
Laker

[logoman]

I wonder if I should try a low strength thread lock first (222), since the very small slotted screw is very prone to damage, and fairly inaccessible too, meaning that it's difficult to apply a medium amount of force to it.

[Laker]

Hello Logoman - yes, why not try the low strength one first - I don't think you have anything to lose, apart from perhaps needing to buy another stronger one later if for any reason you find the low strength one doesn't hold it.
Laker

[KNO3]

Try washing the screw and its hole with alcohol or another degreaser (a small syring or brush helps) before applying threadlock.