|
Dead Cylinder
I have a 8 cylinder 350 (I think GM..it's in a boat)
Engine back fires and sputters. Engine does not leak oil that I know of. (or at least not very much)Compression test revealed 0 compression in 1 cylinder and all others were ok. Based off these symptoms, Is it likely that I will have to do work on the engine block or will the problem be likely in the Head (gaskets or other) |
Head. Gasket or valve.
"nate" wrote in message . .. I have a 8 cylinder 350 (I think GM..it's in a boat) Engine back fires and sputters. Engine does not leak oil that I know of. (or at least not very much)Compression test revealed 0 compression in 1 cylinder and all others were ok. Based off these symptoms, Is it likely that I will have to do work on the engine block or will the problem be likely in the Head (gaskets or other) |
Bill,
You the man! :)...So you don't think I'll have to tear it completely down / take the engine out? Nate "Bill McKee" wrote in message link.net... Head. Gasket or valve. "nate" wrote in message . .. I have a 8 cylinder 350 (I think GM..it's in a boat) Engine back fires and sputters. Engine does not leak oil that I know of. (or at least not very much)Compression test revealed 0 compression in 1 cylinder and all others were ok. Based off these symptoms, Is it likely that I will have to do work on the engine block or will the problem be likely in the Head (gaskets or other) |
Bill,
You the man! :)...So you don't think I'll have to tear it completely down / take the engine out? Nate "Bill McKee" wrote in message link.net... Head. Gasket or valve. "nate" wrote in message . .. I have a 8 cylinder 350 (I think GM..it's in a boat) Engine back fires and sputters. Engine does not leak oil that I know of. (or at least not very much)Compression test revealed 0 compression in 1 cylinder and all others were ok. Based off these symptoms, Is it likely that I will have to do work on the engine block or will the problem be likely in the Head (gaskets or other) |
Squirt about 1oz of 30 to 50 wt oil in that cylinder, enough to wet the
entire circumference and check compression again. If there's no change it should be a valve or gasket. If the compression jumps up it may be a piston/ring which means you need to go into the block. The only other possibility is that a hole in the piston is large enough that the oil won't seal. In that case you might be able to see it with an inspection mirror and a small flashlight through the spark plug hole. LD "nate" wrote in message . .. I have a 8 cylinder 350 (I think GM..it's in a boat) Engine back fires and sputters. Engine does not leak oil that I know of. (or at least not very much)Compression test revealed 0 compression in 1 cylinder and all others were ok. Based off these symptoms, Is it likely that I will have to do work on the engine block or will the problem be likely in the Head (gaskets or other) |
Bill McKee wrote: Head. Gasket or valve. "nate" wrote in message . .. I have a 8 cylinder 350 (I think GM..it's in a boat) Engine back fires and sputters. Engine does not leak oil that I know of. (or at least not very much)Compression test revealed 0 compression in 1 cylinder and all others were ok. Based off these symptoms, Is it likely that I will have to do work on the engine block or will the problem be likely in the Head (gaskets or other) Why? It could very well be a hole burnt in a piston, or a valve broke off and pounded a hole in the piston. Usually if it's the head gasket, you'll show a little compression, but will leak down easily. Same with a burnt exhaust valve. |
|
or the exhaust valve is burned out. When I pulled the head on my 4-cyl
140 the #4 cylinder had a big V-notch burned in the valve, and a burnt gasket between 2 and 3. Head was warped out about 10 thousanth's. New valves, seats, and gaskets and planed. I havent put it together yet, but I'm looking forward to having it run by the weekend. Tim |
Engine back fires and sputters./.."
OOPS, sorry, I missed the backfiring part. I'd say it's an intake valve problem, But I doubt if you need to pull the whole block. jsut the head...BUT, I'd pull them both and have the job done right. You might be doing some preventive maintianence by haveing the other head inspected as well. Tim |
Pull the head in the boat and check it out first. Then you may have a real
problem if the head or valve is not bad. Bill "nate" wrote in message . .. Bill, You the man! :)...So you don't think I'll have to tear it completely down / take the engine out? Nate "Bill McKee" wrote in message link.net... Head. Gasket or valve. "nate" wrote in message . .. I have a 8 cylinder 350 (I think GM..it's in a boat) Engine back fires and sputters. Engine does not leak oil that I know of. (or at least not very much)Compression test revealed 0 compression in 1 cylinder and all others were ok. Based off these symptoms, Is it likely that I will have to do work on the engine block or will the problem be likely in the Head (gaskets or other) |
wrote in message oups.com... Bill McKee wrote: Head. Gasket or valve. "nate" wrote in message . .. I have a 8 cylinder 350 (I think GM..it's in a boat) Engine back fires and sputters. Engine does not leak oil that I know of. (or at least not very much)Compression test revealed 0 compression in 1 cylinder and all others were ok. Based off these symptoms, Is it likely that I will have to do work on the engine block or will the problem be likely in the Head (gaskets or other) Why? It could very well be a hole burnt in a piston, or a valve broke off and pounded a hole in the piston. Usually if it's the head gasket, you'll show a little compression, but will leak down easily. Same with a burnt exhaust valve. When the valve breaks off there is not a little hole in the piston. Normally the piston splits and the rod breaks. And the cylinder can crack also. Makes a little tapping sound before a single big bang sound. Been there, done that. Pistons rarely have a hole burned through them, unless you are running really hard and lean. Then you see aluminum on the sparkplug when you pull the plug. And depending on the size of the head gasket hole, and the speed of the engine turning, you get so little compression, it will not register on the gauge. Takes a couple of PSI to move the gauge. You have to overcome the Schrader valve spring in the tester. Same for a burned valve. And if the rocker for the intake is broken, you also get a zero to very low reading on the compression gauge. |
nate wrote:
I have a 8 cylinder 350 (I think GM..it's in a boat) Engine back fires and sputters. Engine does not leak oil that I know of. (or at least not very much)Compression test revealed 0 compression in 1 cylinder and all others were ok. Based off these symptoms, Is it likely that I will have to do work on the engine block or will the problem be likely in the Head (gaskets or other) A hole in a cylinder top? A bad valve? Stuck open? A broken ring? Not likely a bad gasket, but you will need one anyway. Yank the head. Terry K |
When I pulled mine (1986 350) heads for a stuck valve. Both Heads had
cracks in the Exhaust Seats, clar thru to the water jacket. This is apparently not uncommon for GM small block engines running with a high load. |
Get a cylinder leak down test done. This test wil tell you the condition of
the rings, valves, and where the problem is! Any "good" auto shop should be able to do the test in under 2 hours. "nate" wrote in message . .. I have a 8 cylinder 350 (I think GM..it's in a boat) Engine back fires and sputters. Engine does not leak oil that I know of. (or at least not very much)Compression test revealed 0 compression in 1 cylinder and all others were ok. Based off these symptoms, Is it likely that I will have to do work on the engine block or will the problem be likely in the Head (gaskets or other) |
Bill McKee wrote: When the valve breaks off there is not a little hole in the piston. Normally the piston splits and the rod breaks. And the cylinder can crack also. Makes a little tapping sound before a single big bang sound. Been there, done that. Pistons rarely have a hole burned through them, unless you are running really hard and lean. Then you see aluminum on the sparkplug when you pull the plug. And depending on the size of the head gasket hole, and the speed of the engine turning, you get so little compression, it will not register on the gauge. Takes a couple of PSI to move the gauge. You have to overcome the Schrader valve spring in the tester. Same for a burned valve. And if the rocker for the intake is broken, you also get a zero to very low reading on the compression gauge. I've changed Several head gaskets that showed SOME compression on the gauge. I've never, ever seen a head gasket that would blow a chunk of it out that it wouldn't read anything, seeing how the valve in the tester keeps the pressure reading. Same with an burned exhaust valve. The thing being, in your reply, you acted definitive. You could VERY EASILY be wrong. |
|
I agree with the guy's that indicated it's an intake valve issue. Pull
the valve covers first, see if the rocker or push rod is the problem. I have seen cases where the rocker stud pulled out, but that would keep the valve closed. The valve could be stuck open, in which case the rocker will be real loose. |
I read each post and appreciate everyone taking the time to reply. I'm
going to tear into it this weekend and will post the results. "Capt John" wrote in message oups.com... I agree with the guy's that indicated it's an intake valve issue. Pull the valve covers first, see if the rocker or push rod is the problem. I have seen cases where the rocker stud pulled out, but that would keep the valve closed. The valve could be stuck open, in which case the rocker will be real loose. |
wrote in message oups.com... Bill McKee wrote: When the valve breaks off there is not a little hole in the piston. Normally the piston splits and the rod breaks. And the cylinder can crack also. Makes a little tapping sound before a single big bang sound. Been there, done that. Pistons rarely have a hole burned through them, unless you are running really hard and lean. Then you see aluminum on the sparkplug when you pull the plug. And depending on the size of the head gasket hole, and the speed of the engine turning, you get so little compression, it will not register on the gauge. Takes a couple of PSI to move the gauge. You have to overcome the Schrader valve spring in the tester. Same for a burned valve. And if the rocker for the intake is broken, you also get a zero to very low reading on the compression gauge. I've changed Several head gaskets that showed SOME compression on the gauge. I've never, ever seen a head gasket that would blow a chunk of it out that it wouldn't read anything, seeing how the valve in the tester keeps the pressure reading. Same with an burned exhaust valve. The thing being, in your reply, you acted definitive. You could VERY EASILY be wrong. I could be wrong about what is wrong, but I have seen several head gaskets without compression. And my daughters Explorer broke the intake rocker and zero compression reading. |
Bill McKee wrote: .. And my daughters Explorer broke the intake rocker and zero compression reading. How? Intake valve ALWAYS closed that way. So, when the piston comes up on the compression stroke, both valves would be closed JUST EXACTLY like they would be if the intake rocker wasn't broke. |
Where does it get the air to compress? Pulls a vacuum when the piston goes
down before the compression stroke. wrote in message ups.com... Bill McKee wrote: . And my daughters Explorer broke the intake rocker and zero compression reading. How? Intake valve ALWAYS closed that way. So, when the piston comes up on the compression stroke, both valves would be closed JUST EXACTLY like they would be if the intake rocker wasn't broke. |
ok heres the story,
Pulled the valve cover. Value is moving up and down. cranked the motor until the valves were closed, blew compressed air in spark plug hole, no air came out the exhaust or intake. yanked the head off, no hole in cylinder (that I can see), head gasket look ok from what I could tell Any suggestions? "nate" wrote in message . .. I read each post and appreciate everyone taking the time to reply. I'm going to tear into it this weekend and will post the results. "Capt John" wrote in message oups.com... I agree with the guy's that indicated it's an intake valve issue. Pull the valve covers first, see if the rocker or push rod is the problem. I have seen cases where the rocker stud pulled out, but that would keep the valve closed. The valve could be stuck open, in which case the rocker will be real loose. |
First, I hope you were correct in your original test resulting in "zero"comp
in one cyl. If you don't see anything unusual, looking at the top of the "bad" cyl, compared to the others, look closely at the valves at the seat area. You could have some burned pitted area there. You will need a valve spring compressor which you can buy for $20-30 bucks at the local ap store or possibly rent. When you "blew comp. air in spark plug hole", did you seal the air source (with a rubber or threaded fitting to the hole where you had a "sealed" system and heard no air leaking, at 100-150psi? Or, did you just blow air into the hole and hold your hand over the exhaust/intake? I hate to say it but if you can't see anything "unusual" with the valve/seat, or the gasket or the top of the piston, or, some marking/scoring on the cyl wall w/piston at bottom, you may have mis-read the gauge or not seated it properly on that cyl. I think a week spring/sticking valve was already covered and you need to remove it to check (along with the seat). I would say there's one other possibility but it would have to affect all cylinders. That is a slipped chain on the camshaft, which would change the valve timing, possibly resulting in the two conditions you mentioned--backfiring and zero compression--but would affect all cylinders equally. "t" wrote in message .. . ok heres the story, Pulled the valve cover. Value is moving up and down. cranked the motor until the valves were closed, blew compressed air in spark plug hole, no air came out the exhaust or intake. yanked the head off, no hole in cylinder (that I can see), head gasket look ok from what I could tell Any suggestions? "nate" wrote in message . .. I read each post and appreciate everyone taking the time to reply. I'm going to tear into it this weekend and will post the results. "Capt John" wrote in message oups.com... I agree with the guy's that indicated it's an intake valve issue. Pull the valve covers first, see if the rocker or push rod is the problem. I have seen cases where the rocker stud pulled out, but that would keep the valve closed. The valve could be stuck open, in which case the rocker will be real loose. |
Problem found!
After taking the head off. I poured water into all the intake ports. They all held water except for the valve in question. The water poured right out. I took it to the machine shop to have the valve or head replaced. "t" wrote in message .. . ok heres the story, Pulled the valve cover. Value is moving up and down. cranked the motor until the valves were closed, blew compressed air in spark plug hole, no air came out the exhaust or intake. yanked the head off, no hole in cylinder (that I can see), head gasket look ok from what I could tell Any suggestions? "nate" wrote in message . .. I read each post and appreciate everyone taking the time to reply. I'm going to tear into it this weekend and will post the results. "Capt John" wrote in message oups.com... I agree with the guy's that indicated it's an intake valve issue. Pull the valve covers first, see if the rocker or push rod is the problem. I have seen cases where the rocker stud pulled out, but that would keep the valve closed. The valve could be stuck open, in which case the rocker will be real loose. |
| All times are GMT +1. The time now is 11:48 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004 - 2014 BoatBanter.com