Force 35 - low compression

I bought a used 1986 Force 35 two years ago which sat while I finished building my boat. Now that I am ready to start using it I have taken it to two different marine repair places for compression checks. One came out at 100/125, the other at 80/125. I believe it is the bottom cylinder with the lower compression rating. Here is my dilemma. The guy I bought it from says that I just need to run it for a few hours and that may take care of it, that the rings will probably reseat and all will be well. The two repair shops I took it to say its more serious than that. I don't want to go to the expense of a total rebuild, but I also don't want to give up on this motor just yet. Can anyone out there suggest what steps I should take to figure out what the problem is? Probably not a head gasket, since only one cylinder is low. I suspect it is piston rings, but if anyone has ideas as to what else the cause may be and how to diagnose and/or fix it, I would be grateful. I hesitate to run it until I've checked it out a bit more so as not to compound any possible damage further.

Re: Force 35 - low compression

Hey PeteB,<br />I'd go ahead & pull the head. Even though only one cylinder is low, it could still be a blown gasket. Of course with the head off, you can take a good look at the condition of the cylinders & pistons, plus get an idea of any carbon buildup problems (which can cause sticking rings & a resulting loss of compression). <br />Another tack would be to decarbonize (assuming you can get the motor to run). There are many threads on the board relating to the actual process.<br />Good luck & let us know what you find out.

Re: Force 35 - low compression

I would start with a good decarbonizing and see what the reading is after that. The shops you took it to would prefer to either sell you a new motor or rebuild yours. I have owned several outboards that had at least one low reading that came up substantially, some after running, others took Power Tune to free the rings. It's worth a shot to try it out before the repair $hop$ gets a hold of it. Good luck!

Re: Force 35 - low compression

I agree 100% with both guys, I have the same <br />exact engine, remove the head it is very easy<br />and do a complete decarbonization, inspect the cylinder walls while you're there.<br />I would also remove the exhaust port cover and clean all carbon build up thoroughly.<br />Re-check compression and go ahead and run the engine for a while then recheck the compression. You can rent a compression guage<br />or borrow one from a friend or garage.<br />I do not have a manual for my engine, would love to get one , but this engine is surprisingly simple to work on.<br />Best of luck.

Re: Force 35 - low compression

My 96 force had stuck rings which caused low compression. Try decarb. but prepare to do tear down. I couldn't tell much from just pulling the head but found the problem during disassembly. Good luck!

Re: Force 35 - low compression

another suggestion if you know what parts you need like you will need a head gasket order ahead of time I just rebuilt my motor and waiting for parts took longer than the rebuild took me 3 days to do that takes week to weeks to get parts good luck