Re: Engine compression???
I keep reading about engine compression on the forum. They all state that the compression should be 100 PSI or higher. Is this true of all size engines. I did a compression check on the 7.5 that I recently purchased. It registered only 90 #'s on each cylinder. Is that low for this small of an engine??? The engine starts and runs exceptional so it was my thoughts that the compression for this unit was about where it should be. Am I wrong here??? Thanks for any reply.
Steve
Steve, most of the posts you're reading are about mid-large motors. Dropping a couple of hp in one of those is no big deal and in fact loosing a cylinder often goes unnoticed..
You can't say that about the small engines so Merc engineers have to design them to a much higher degree of excellence. They need to start on the first pull, run smoothly and often under extreme conditions.
Like JB say's, in most cases, as long as the small motor has 50psi cold compression it should run but you might find it no longer starts on the first pull like it did when it was new. As long as it's fairly even on two or more cylindered engines it will also run smooth.
I think your motor is just fine. If you notice it beginning to idle roughly and you don't suspect fuel or spark then look at the compression again. Otherwise, I think it's got quite a few years of service left in it if you take care of it. Just remember, the biggest killer is improper winter storage.
