88 Comp with low compression in one cylinder?

[supra88']

I'm pretty new to this forum and have got some GREAT info from you guys. I go to the lake at least 3 or 4 times a week and we do a lot of wakeboarding (even tho I'm not great cause im always stuck driving everyone else lol) and I have noticed the boat is starting to struggling a little more out of the hole shot. So yesterday I did a compression test on my 351w and all the cylinders were between 110-115, but one was 100 and another was only 70. I put a little oil in the 70 psi cylinder and checked it again and it did not come up very much, maybe 5psi... Looks like I have lost a cylinder and I know this is bad, but exactly how bad? Pretty sure a rebuilt is not too far in my future...

Thanks

[Kma4444]

If oil didn't affect the compression that likely means it's not a ring or piston issue. More likely a valve sealing or head gasket in order of likelihood. It also could be a valve train issue, for some reason a valve isn't opening all the way but again that's pretty unlikely. I would think by pulling the head you will discover the problem pretty quickly. If it's just a valve issue then a trip to the local engine machine shop should have you up and going pretty quickly and for not a lot of coin. Shouldn't take a shop long to turn the heads around so no reason to be down long.

[supra88']

Thanks, yeah I'm not a motor expert but I try to do as much as I can on my own. Mainly getting my info from this forum. I will try to find an engine shop somewhere here in Jackson and see what they can do about it.... Would it help if I put a heavier weight oil in it? Or is there anything I could do that would "help" it out until I get it to a shop?

[Kma4444]

Not really anything you can do to affect the compression in one cylinder without mechanical repair. Good news is they are really really really simple animals and if you have any mechanical background or proclivities, then you can absolutely take on the task of removing the heads yourself. It's not hard, the absolute worst thing you might run across is broken bolts that would complicate the job. That's not that big of a deal. just ask any questions you want and I'm sure you will get an answer. Wouldn't be surprised if there is someone close that wouldn't mind coming by and offering advice if you needed it.

[DAFF]

I would keep running the engine till the season draws to a close. If there are no bangs or smoke you might be down a little power but still out on the lake. Fall is going to hit early this year and winter more than likely front heavy.

[supra88']

Could you give me a quick summary on how I would pull the heads? I have heard that you got to pull the whole motor out if your going to take on that big of a task... I had the boat out yesterday and I can really tell that I have lost a lot of power out of the hole shot since the beginning of the season. Thanks again

[Kma4444]

Basically it involves removing the intake manifold, the exhaust manifolds and then the heads. That's an oversimplification but it also really is the extent of it. Things like removing water hoses can be a pain since they can be quite stuck after you remove the clamps but nothing in there is all that difficult. Come up with a simple way of organizing parts so you have all the bolts and pieces in groups so there is no confusion of what goes where. There's a fair number of pieces when it's disassembled but nothing overwhelming. Patience, lots of pictures and a lifeline to call or have come over is all you should need.

I can't imagine any reason to remove the engine from the boat to do the heads.

[DAFF]

Pull the valve cover off and bump the engine over while looking at the valve springs.... Perhaps you have a broken spring or a push rod broke the rocker arm off.

[supra88']

Thanks guys, I'm probably going to do that during the off season cause I'm out on the water at least 4 times a week. I guess this will give me something to do this winter... Might even just rebuild it