Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Howdy Phil .... and welcome from the Eastern Sierra!

Yes, they should have compression on every other revolution so it is likely that your O-ring has failed. It is quite easy to check this by simply removing the head (6 bolts) and splitting the crank bearings on the big end of the piston rod (2 bolts). Then you just push the piston up out the top of the cylinder far enough to check your O-rings and replace them if they are not right. I've heard that anything from 20 x 1 to 22 x 1 mm O-rings work fine, and you will want to get ones that are resistant to hydrocarbon compounds like gas and oil.

It is also possible that one of your valves is stuck slightly open, which would also kill compression, but which can also be checked for once the head is off.

I've found Coleman fuel to work fine, though there are other fuels these low compression engines work well on also.

There are a number of threads about these engines, with a vast amount of good information, so I'd suggest you tour around the Forum and check several of these out for more detailed information!


Try checking these threads:

https://www.officeofsteamforum.com/general-discussion-scale-model-gas-engines-hit-miss-throttle-governed-non-compression-etc/eachine-et-1-adjustment-and-fixing-(fiddling)/

https://www.officeofsteamforum.com/general-discussion-scale-model-gas-engines-hit-miss-throttle-governed-non-compression-etc/microcosm-m90-hit-miss-engine-arrived/

https://www.officeofsteamforum.com/general-discussion-scale-model-gas-engines-hit-miss-throttle-governed-non-compression-etc/yet-another-m90-hit-n-miss-thread/

 .... and there are others as well.