'81 300 Compression
Thread Starter
|
Senior User
Joined: May 2005
Posts: 247
Likes: 0
From: Ethridge, TN
'81 300 Compression
I have not been able to work on the old truck for a few weeks, so Sunday afternoon I spent 1/2 hour checking the compression. I found:
#1 - 20 lbs
#2 - 25 lbs
#3 - 65 lbs
#4 - 70 lbs
#5 - 25 lbs
#6 - 65 lbs.
I squirted oil in each cylinder to see if the pressures came up, but they didn't. I'm thinking that I have either a blown gasket between 1 & 2 or maybe stuck or burnt valves in 1,2 & 5. I plan on taking the valve cover off this weekend and see if the valves fully open and close when cranking. The engine will try to start, but just wont quite do it.
Any other ideas?
Thanks.
#1 - 20 lbs
#2 - 25 lbs
#3 - 65 lbs
#4 - 70 lbs
#5 - 25 lbs
#6 - 65 lbs.
I squirted oil in each cylinder to see if the pressures came up, but they didn't. I'm thinking that I have either a blown gasket between 1 & 2 or maybe stuck or burnt valves in 1,2 & 5. I plan on taking the valve cover off this weekend and see if the valves fully open and close when cranking. The engine will try to start, but just wont quite do it.
Any other ideas?
Thanks.
Posting Guru
Joined: Apr 2003
Posts: 1,903
Likes: 2
From: Wyoming
All those number seem low. How many miles on that engine, and did it sit idle for a long time? I read your other posts, and got sort of a feel for your problem. Sounds like you ruled out rings with the oil squirt trick. The valve cover needs to come off next, as you mentioned.
When you did the compression check, did you have all 6 spark plugs removed and crank at least 6 times per cylinder? They should be up around 90 - 125 psi. The Ford manual's rule of thumb about all cylinders being within 75% of each other is hardly helpful if they are all 25 psi.
Maybe you can use part of your compression check equipment to run compressed air into your bad cylinders and see if it leaks out the intake or exhaust.
When you did the compression check, did you have all 6 spark plugs removed and crank at least 6 times per cylinder? They should be up around 90 - 125 psi. The Ford manual's rule of thumb about all cylinders being within 75% of each other is hardly helpful if they are all 25 psi.
Maybe you can use part of your compression check equipment to run compressed air into your bad cylinders and see if it leaks out the intake or exhaust.
Thread Starter
|
Senior User
Joined: May 2005
Posts: 247
Likes: 0
From: Ethridge, TN
Spikedog,
It sounds kind of low to me also. I could not find a min pressure in the manual I have either, all I found was low cylinder 75% of high. I had all six plugs out and cranked probably 6-8 times each. I'm not sure how long the truck has sat either. It's got a factory re-man engine in it so I'm not sure how many miles are on it.
I was thinking of the same trick as you were with the compressed air. Maybe I could find if the exhaust or intake valves were leaking.
Thanks for the comments.
It sounds kind of low to me also. I could not find a min pressure in the manual I have either, all I found was low cylinder 75% of high. I had all six plugs out and cranked probably 6-8 times each. I'm not sure how long the truck has sat either. It's got a factory re-man engine in it so I'm not sure how many miles are on it.
I was thinking of the same trick as you were with the compressed air. Maybe I could find if the exhaust or intake valves were leaking.
Thanks for the comments.
Posting Guru
Joined: Jun 2004
Posts: 1,635
Likes: 0
From: Niceville, FL.
When doing the compression test the throttle should be "wide open", but you probably already knew that. I'd also try spraying some WD-40 in the intake while spinning the engine (plugs installed) to see if it would "free up" any stuck valves. If you can get it started, I'd use a can of "Seafoam Engine Cleaner" poured through the carburetor per instructions on can. I've seen that work near miracles on engines with high mileage or having not been run for extended times.
Thread Starter
|
Senior User
Joined: May 2005
Posts: 247
Likes: 0
From: Ethridge, TN
I pulled the head off this weekend. It had a burnt valve on #2 and almost all of the rest of the valves weren't seating properly. Also, the head gasket was leaking between #1 & #2. Hope to get it back on in the next couple of weeks.
Thanks for the replies.
Thanks for the replies.
Thread
Thread Starter
Forum
Replies
Last Post
Ziggy.
1999 - 2003 7.3L Power Stroke Diesel
25
Aug 25, 2021 07:56 PM
ramarado
FE & FT Big Block V8 (332, 352, 360, 390, 406, 410, 427, 428)
3
Jul 2, 2010 10:52 PM
