I have many years experience of Nitro engines in R/C aircraft but am new to buggy engines.

I recently bought a second-hand 1/8 off-road buggy which has a Force 28 engine in it. When I start the engine up it runs nicely for about 10-20 seconds then stalls and siezes/jams. The pullstart will not turn the engine at that point. If I remove the glow plug and rock the flywheel (it only moves a tiny fraction each way) I can just see the slightest movement in the piston head up/down but the engine just will not turn more than 1 or 2 degrees either way.

Any ideas what is causing this and if it is fixable please, or what I can check on the egine to investigate further? I am told by the previous owner (!!!) that the engine ran okay (!!!).

Any help appreciated. Many thanks.<br type="_moz" />

If the engine is new, then this is normal. Preheat the engine before starting. Never let the engine sit with the piston at TDC. Use a screwdriver on the flywheel to free the lockup.

Thanks for the feedback.

The engine is definitely not new (the spare/damaged cooling heads that came with it are a good clue to that). I don't see how I can stop the engine from stopping at TDC if that is where it decides to stop (and jam); is there an external indication as to where the piston is in its cycle without removing the glow plug?

Also, I don't understand what you mean by using a screwdriver on the flywheel to free the lockup; my mole grips on the flywheel woudn't free it up for ages; how do you go about using a screwdriver to do the same? Just curious in case I am missing a useful trick.

Many thanks.<br type="_moz" />

the engine has pinch at TDC...this is normal with every nitro engine, even airplane engines.....

no this is something different... this happens when your main bearing cage fractures and disperses itself inside the crankcase. this gets stck in the groove between the piston and sleeve, causing it to jam. happened on my thundertiger .12 just before it finally seized.ended up buying a shortblock for it and it runs like a champ now.

An old engine that acts like a new engine with pinch. Strange. You'll have to, at least, take offthe backplate and check for damage.

Use a flatblade screw driver between the flywheel and chassis cutout to turn the engine crank. Once free, rock the flywheel back and forth. It will be tight at TDC. So in between will be close to BDC.

Old engine could have been pinched maybe...taking engine apart is only thing you can do at this point ( as others have said )

I'm not particularly familiar with car engines but this doesn't sound like a pinch problem because the piston can be seen to move slightly. I'm more inclined to think it's a problem with the pull start mechanism.

Do your self a favor and take the engine out and take it apart to look at the inners. I had the same problem with the same engine and what it ended up being was that one of the balls from the ball bearings dislodged it self and bassically DESTROYED the inners. Litteraly part of the piston shaft broke off and lodged itself by the rest of the shaft making it have a Pinching feeling. Ended up just buying a new engine. I hope its not that case for you but what you described was the same exact problem i had

A quick update on this; the piston actually seemed to be hitting the underside of the glowplug once the engine had reached a certain temperature. I have added a (0.1mm) shim under the button head and the problem seems to have gone away! However, the engine has still proven to be a bit unreliable but as its history is unknown to me it may just be badly worn.

What is the overall reliability / longevity of a Force 28 like? Are they reasonable engines?
(Just wondering in case I choose to buy a new engine, wondering whether to replace like for like or get something different).

Are you using a long reach plug? Because there are three lengths. 'Long reach', 'normal' (or something called 'car'), and 'short reach'. You may have one that is too long. The underside of the plug should fit flush with the dome of the head. It should not protrude into the combustion chamber.

I attempted fixing my force .28 it was never right from the start and now i finished "the job" my engine had a bad carb, backplate, and the piston was also very tight at TDC, at TDC you could feel the crankshaft click one way or the other when the con rod shifted. very odd.



however force engines are usually pretty well made and reliable, i had a force .12 that never quit, it just depends on who owned it before you.

Normal, especially when cold.