Stuck valve & why 2 head gaskets

Hogheaven · Jan 24, 2015

I dont know the engine, perhaps the head was warped and they were trying to compensate instead of heading to a machine shop.

jtuner119 · Jan 25, 2015

I recently bought a Catalina 30 with a 5411 universal Diesel engine that had a stuck valve. Currently the head is at the machine shop waiting for seals. The head has to be resurfaced due to some corrosion and a shim may be necessary. That could be what your looking at. A head gasket and a shim. Unless it's actually 2 head gaskets, which does not make sense at all. I've heard of some backyard mechanics, that don't know what they're doing, repairing a head gasket and not removing the old gasket. I don't know anything about atomic engines but service manuals are a big help. Good luck and congrats on the new boat.

Afrakes · Jan 25, 2015

Go to the Moyer Marine web site. They'll have the correct answer there.

The Garbone · Jan 25, 2015

2 head gaskets is correct as per the rebuild manual. Check out Moyer Marine, super resource for the A bomb.

Anonymous 121765 · Jan 25, 2015

On why two gaskets?

It's a common practice on cars & I found that I had two on my old 5411 Universal.

CR

RichH · Jan 25, 2015

nlneilson said:
Started tinkering with the Atomic 4 engine in the boat I recently bought. No compression in the back cylinder. Took the exhaust manifold and head off.
A real PITA. the stud that is in the back of the thermostat was corroded and stuck in the head. Finally got it off and freed up the valve on the very rear.

Where is the serial number on the engine ??

There were 2 head gaskets but I don't understand why. That would just reduce the compression ratio. Is there supposed to be 2 ??

Studs - use a dedicated 'stud puller' (Snap-on tools, etc). When doing your yearly, etc. maintenance cylinder head retorque, if you notice that a stud has elongated/stretched ... with a stud puller you dont need to remove the head to replace a stud if you have a dedicated stud puller. Pulling the studs before head removal is the way to go.

Two head gaskets - At the cessation of the many year production of the A4 (~mid 1970s) many INDUSTRIAL stationary versions of the A4 were released from stock to various boat builders. These engines developed slightly higher compression ratio, and were more prone to 'blowing' a head gasket. The double head gasket slightly decreases the compression ratio and makes the engine less prone to blowing a head gasket. To determine if the engine has a 'shaved down' head ... go to the www.moyermarine.com website, go to the forums and look up the dimension of 'thickness' of the head. That your engine has two head gaskets possibly indicates that your A4 was one of these 'industrial version' OR that the head was previously 'shaved down' to remediate 'warpage'.

Serial Numbers are stamped into the side of engine block .... I forget which side.

If youre self-maintaing your A4 (a damn good idea), suggest you obtain a copy of the - Moyer A4 Maintenance and Rebuild Manual. It will save you $$$ and lots of 'swearing time'.

RichH · Jan 25, 2015

Oops ..
If the exhaust valve in Cyl. #4 is stuck .... do a 'pressure hold' test on the 'waterside' of the exhaust manifold. Stuck exhaust valves on an A4 are an indicator of a pin-hole leak in the ex. manifold.
If the valve is stuck and the head isnt off, you can make up an "L" probe out of a stout screwdriver with which you can reach into the combustion chamber to push it back down. That plus a liberal dose of a 'penetrating oil' on the valve stem (remove the side plate) ... a few 'push downs' and the valves usually will stay 'free'. Doesnt apply if there is a pin-hole leak in the ex. manifold which keeps draining back to the affected cylinder through its exhaust valve. Check (pressure check) that ex. manifold !!!!! ;-)

celticwinds · Jan 26, 2015

Definitely check the manifold. Look for any water on the spark plug or signs of it in the cylinder. Two head gaskets is correct. Be sure the head bolts are screwed in to all of the threads in the block to keep from damaging the block when you torque the head nuts down. The threads do not go very far into the block and can be ripped out easily. Be careful and don`t over torque the nuts. Torque is only 30 to 35 foot pounds. Get a repair manual from Moyer Marine. Use Marvel Mystery oil in your gasoline. The torque for the manifold bolts is not very much either so check the manual for correct specifications. I work on an a 4 for a friend that has a 1971 Pearson 30 and have done head gasket, manifold, carb, coil, tune up, fuel pump rebuild,head bolt repair, but no valve work like you described.

Anonymous 121765 · Jan 28, 2015

Just a reminder,

After running the engine at operating temperature & after the engine has cooled completely (like the next day), check the torque settings again. Many times, some bolts may need to be tightened a bit more.

I told a friend once to do this check. He didn't & a week later the new gasket failed He ended up with salt water in his pistons. I checked his torque settings & some bolts had not seated. This is important if you've had the head refaced.

CR

celticwinds · Jan 28, 2015

There is definitely a tightening sequence for the nuts. If you don`t see it in the manual then I would google it.