1990 7.4L compression test results
 

The story;

Two years ago I experienced a drop in rpm's to about 4200-4300. I took it to a marina and asked them to check out the engine. The said that it needed a complete rebuild which they could do over the winter. Well I never had them do the rebuild, the boat has just sat in my warehouse for two years. Recently I've been trying to decide whether to rebuild it or repower not knowing if I was going to keep the boat or not. I haven't had great success with this marina in the workmanship or trust arenas. I decided that I would play around with it a bit this week. Well after two years of sitting it fired right up, sounds great, and runs (idles) smooth. This morning I did a compression test and here are the results;

The proceedure;
1) I warmed the engine up (about 150 degrees)
2) Removed flame arrestor
3) removed all plugs
4) throttle wide open
5) checked in the following order;

1) 141
3) 125
5) 130
7) 132
2) 132
4) 107 retested 107
6) 120
8) 130
1 again) 137

The engine currently has 525 hours on it. I imagine I still have the lower than expected rpm issue that I had a couple years ago. Based on these numbers does anybody have any opinions of what I should do? If your in the michigan area please forward names and numbers of shops that you recomend do the work.

Thanks

Keith

Re: 1990 7.4L compression test results
 

I agree with formula. Keep running it till it really goes south. Then either get yourself a new/rebulit shortblock & have the heads redone. Or spend a few bucks more and buy a new/rebuilt engine complete.
Gary

Re: 1990 7.4L compression test results
 

thanks for the replys guys. I'll try squirting the water into it to try and clean it first.

Re: 1990 7.4L compression test results
 

Thanks, hey you never know what I just might do at times :)

Re: 1990 7.4L compression test results
 

You could also squirt some oil in the low reading hole and retake the compression reading. If the compression comes up, need rings. If there is little change, valve job. I'm betting on valve job.

BT :cool:

Re: 1990 7.4L compression test results
 

Where are you in Michigan. I can recommend someone in the Grand Rapids area.

Re: 1990 7.4L compression test results
 

It really doesn't matter much where they are in but I'm in Howell (about halfway between Detroit and Lansing)

Re: 1990 7.4L compression test results
 

Does not sound too bad for the hours and all. But, after 500+ hours your valves and springs are done. I'm sure if you did a leak-down the top end will be the culprit.

Tired valve springs make a very effective rev-limiter.

Kurt
.

Re: 1990 7.4L compression test results
 

If those are stock Mark 4 peanut port heads which Im guessing they are, Ive got at least 2 pair in very good (recent rebuild) condition.

Tom

Re: 1990 7.4L compression test results
 

Hi. I'm in Livonia. I can do your rebuild for probably 1/2 the marina price. Let me know if you are interested. I just did a 5.7L which you can see+hear run to verify my work.