migara422

Hi guys, i blew my head gaskets a month ago i had this guy fixed it, took the heads to the shop and did a valve job also, last weekend i took it to the lake and on my way back started missing above 3000 rpms, he just now checked it and told me over the phone that one of the plugs was closed, like it had hit something, maybe debris from changing the heads, who knows, he did a compresion test and all cilinder about 165 but this particular one 140, im gonna go see him tomorrow but i would like to know things about this problem so i can bomber him with questions on this.
Any help would be appreciate it.
BTW the motor is a marine 502 crate motor

Reed Jensen

Did the mechanic just remove the head and do a valve job?.. or did he disassemble the engine and inspect?... You may have a broken compression ring... or maybe some scuffing in the cylinder wall.. possibly some corrosion "etched" the cylinder wall when it got wet.. Here is a photo of a Jag engine that had a blown head gasket... the customer asked me.... "Why can't we just change the head gasket... Why do we have to disassemble the engine if only the gasket has gone bad?".... I knew this was what I was going to find after disassembly... his reply" But it was running when I shut if off... it didn't just die.".... " I just don't understand why the engine has to come apart".... I'll let you guys judge for yourself it the engine should have come apart...

Reed Jensen

Here... I'll give you guys a closer look........

Griff

Have him do a leak down test on the low cylinder. If it comes back bad, then have him do a leak down on all the cylinders.

There should not be any debris that could have hit the plug, unless he left it in there.

The closed plug would cause the miss. Post a pic of the plug.

migara422

He only took the heads off and do a valva job,actually he took it to a machine shop , i did see the motor without the heads and it didnt look bad, man that engine looks ate up Reed, i will get the plug today and get a pic griff, thanks guys.
Carlos

cig1988

P.S. when the leak down test is performed and you have a considerable amount of loss... listen very carefully where the shop air is coming from.
exhaust= exhaust valve
carburator=intake vavle
crankcase=rings

migara422

I went to see the mechanic today and he had the valve covers off and he said he retested the compression and the same cilinder was now 120 before 140 the others 175 lbs, the spark plug was not completely close but you coulnt put a hair through it, he said he put the new plugs and it didnt close this time, the miss still there and he thinks it could be the piston,bearing or the pin, when it left the shop there was nothing wrong with it, on the hose of course, took it to the lake and on way back to dock its when started missing, my question is that Is it possible that this happened because i overheated the engine before? and if yes, why didnt it do it right when everything was put together? It ran ok for about an hour then it took a crap, or maybe he did something wrong when he put it together? dont want to blame someone but im not a mechanic and im sure some of you have seen all scenarios>
any help would be appreciate it

Reed Jensen

Who knows?.... but a blown head gasket is usually the symptom.... not the problem... why did the gasket go in the first place?... over heated? warped head? In those photos of that Jag engine I posted... both the head and block had a warp... the block was .012 of an inch higher at the ends than in the middle... and the head was almost the same way... All the head studs had to be removed and the block "decked"... The engine had just warped over time.. Iron blocks have a tendency to do that... so... Back to your problem... What if the deck on your engine has a warp?... Did your mechanic check that with a straight edge? Maybe the new head gasket is leaking already... and small amounts of water are getting into the combustion chamber and fouling the mixture?... When ever a customer comes in with an Aston that has a blown head gasket... I make them tear the engine down... but that is a different problem all together. They have "wet liners" with O-rings that seal at the bottom... take the head off... and the cylinders always leak at the bottom... water in oil... not a good thing...

Raylar

Migara422
As suggested in earlier posts have a leakdown compression test done on the motor. After the low cylinder is checked, squirt a little motor oil in the affected cylinder and then retake a compression test on that cylinder, if the compression rises 10 to 20 lbs, you most likely have damaged the rings or piston, if the compression does not go up at all the valves in that cylinder or the head gasket is still leaking and needs to be taken apart and redone carefully with the head being magnafluxed and the cylinder head and block surface rechecked for warpage or uneveness. The biggest problem in blowing head gaskets in boats is the overheating and water intrusion into the motor. Make sure if you don't feel comfortable with the mechanics ability you need to switch to a competent marine engine mechanic.
Good Luck, hope its minor,
Raylar

John B

I'd be concerned about what closed the spark plug gap!?