no compression cyl 1&2 912 ULS

[turboturner]

thnx for writing, gents.
Compression gauge is in PSI. I discovered the problem by hand-turning the prop & noticed the “reduced” compression. That the two fwd cylinders would lose compression simultaneously is indeed strange. Yes, could be sticky valves, but both at the same time? Engine will not start.

[Slyfox]

a strange one but if running 100ll very possible. I would remove the valve covers and check to make sure the valve are being pushed in. compare to the good cylinders. I don't have the firing order on hand would that be the two front cylinders like a lyc. next would be to do a differential compression test to determine if it's intake valve, exhaust valve or piston rings. that should get in the right direction. like I said earlier, you can take the covers off. Then smack each valve to see if they are stuck. try another compression check.

[turboturner]

thx for the recommendation DW. Do you use it because you run mostly on 100LL? Just wondering if it’s as effective on Mogas. Read that Decalin is a solvent for resin (?). Could it have an effect on fibreglass fuel tanks? In any case, adding a carbon cleansing agent regularly to the petrol seems like a good idea. I’m sold!

[Delta Whisky]

Carl - I use only 100LL (not because I want to) and the Decalin is used to avoid or at least minimize lead deposit build up. Lead build up will do the same to engines as carbon will but (in my experience) more frequently and in more places. Decalin causes the lead to end up in a different compound during or after the fuel is combusted and it flows out with the exhaust rather than building up. I've not come across it being used as any kind of cleaner - can't talk to that - but my tanks have not (yet?) shown any deleterious effects.