1990 7.4L compression test results
#1
Registered
Thread Starter
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
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
#2
Registered
Join Date: Jan 2001
Location: ST. Louis, MO, USA
Posts: 1,658
Likes: 0
Received 0 Likes
on
0 Posts
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
Gary
#4
Registered
Thread Starter
Re: 1990 7.4L compression test results
Originally Posted by formulaz583
You a spray bottle. do NOT just dump water in it. I figure that you know this, just wanted to be sure.
#5
Registered
Join Date: Nov 2001
Location: Pennsylvania
Posts: 3,385
Likes: 0
Received 0 Likes
on
0 Posts
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
BT
#7
Registered
Thread Starter
Re: 1990 7.4L compression test results
Originally Posted by MACDAD260
Where are you in Michigan. I can recommend someone in the Grand Rapids area.
#9
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
Tom
#10
Registered
Join Date: Jan 2004
Posts: 112
Likes: 0
Received 0 Likes
on
0 Posts
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.