compression

[mAlton]

If one cylinder has compression at 10 less than the other cylinders; how bad is that? Should I be worried or is it ok? Thanks.

 

[waffles1]

Re: compression

You are fine. I have a 89 suzuki dt85 and my compression has been 120/120/112 for many years and th emotor runs like a champ. Are you experiencing some problems or was this just a curiosity question?

 

[JB]

Re: compression

Ten what?? 10psi? 10%?

Ten percent is the measure, or usually 10-15%.

Waffles has a difference of 8psi, about 7%. Neither of those is ten.

 

[rodbolt]

Re: compression

depends on the engine,some yamahas have as much as 15 psi as designed.

 

[mAlton]

Re: compression

Thanks guys for the responses. I was having a bogging down problem that I thought was electrical, but a shop foud to be a fuel line collapsing. However, they told me my compression is 92-100-100-102-102-102. They also said that the cylinder at 92 seems to be running at 10 degrees hotter than the rest. I was trying to figure out if I should sell this boat and get another or run it for a while. I really don't want to lock it up because it will be worthless at that point. Thanks again for the replies.

 

[waffles1]

Re: compression

What did the shop suggest? What did they say about the cylinder running 10 degrees hotter? Did they have a theory on why? It sounds like it is getting less oil then the others or not getting as good water circulation as the others. I am not an expert but is 10* a big deal? I'd love to hear an experts opinion on this just for my, and maybe others, future reference.

 

[mAlton]

Re: compression

I'm not sure either, but I am nowhere near a mechanic. I didn't think they were trying to get me to trade it in, because they really didn't push the idea to hard. He just suggested that I shouldn't run it hard (over 4,000 rpm) and not open it wide up from a dead stop, but be gentle with it. The whole idea confused me and I just don't want to tear anything up and make it worthless. As for why it would be hotter, he had no idea about that either. I was kind of surprised that he could even tell it was hotter to begin with. Thanks.

 

[Fl_Richard]

Re: compression

What would you say if mechanic said your car will be fine, just keep it under 55 and be sure not to accelerate to quickly or really get on it to pass someone?

I say decarb fully and test the compression again.

Then get another mechanic.

 

[99yam40]

Re: compression

Only one person knows what motor is being talked about in this thread and if he has been running it lean because of fuel delivery problems there may be a problem with the motor.
You can have it leak down tested,or pull the heads to see what the cylinders and pistons look like, or bore scope to see if you can see anything.
But if you do have a problem make sure you price it properly, you don't want to screw the next owner if you sell it.

 

[mAlton]

Re: compression

Well, the gamble was too much for me. I sold the boat today. I was open about my concerns to him. I showed him the paperwork from the shop with the compression results and even printed out these responses for him. He seemed to think it was going to be ok. I hope it is, but I was worried that it was going to be a big problem someday if I kept it. Thanks again for the replies and advice. Now I have to start looking for a newer boat.

 

[Silvertip]

Re: compression

Do a decarb and rebuild the carbs. The decarb alone may bring up that cylinder. A cylinder running lean will run hot and since it is lean on fuel it is also lean on oil. Continue that mode and you risk burning down that cylinder. Both procedures are cheap. If it doesn't help you are out just a few bucks and some time. If it helps, you prevented a catastrophe.