Cylinder Head rebuilt recommendations

[libarra82]

Hi All,

I have a 1987 NA 944 with 78K miles. I've been slowly restoring it for the last 6 months. I've done the water pump, belts, rollers, fluid changes, vacuum lines. Overall it runs well but I've notice a tapping sound from the engine. Cant no longer hear it once the engine is warmed up, unless I'm at a stop next to other cars, or standing in front of it with the hood open. Car sat for 4 years before my ownership, I'm thinking it could either be a collapse lifter, exhaust leak or bent valve.

I decided to investigate further and purchased an automotive stethoscope and a engine compression gauge. Using the stethoscope I listed to each lifter. All lifters sounded identical except the very last one at the back, it had a loud metal tapping sound that matched the timing of the tapping sound I've been hearing from the engine.

Next I did a compression test. Cylinder 1 = 140 Cylinder 2 = 140 Cylinder 3 = 140 Cylinder 4 = 0

Most likely #8 valve is bent, or hopefully blown head gasket . I'm going to start disassembling the engine for further inspection. If the valve is indeed bent, I'll be replacing it along with all the seals, gaskets for both head and cam tower at minimum, if I don't find any other damage. Question is how far should I go with this rebuilt considering the engine only having 78k miles. Should I replace the springs, guides, anything else? I would like to do most of the work myself but would consider taking it to a machine shop for valve and head maintenance.

[michaelmount123]

Where are you located?

The lower end is likely servicable with only 78K miles. This suggests you only have the cylinder head reconditioned. Ideallly you should send or take it to a competent machine shop that's familiar with the 944 so that suitable parts and specs are maintained.

Since you apparently have one dead cylinder, you'll be quite pleased with the result.

[Tom]

Hi All,

I have a 1987 NA 944 with 78K miles. I've been slowly restoring it for the last 6 months. I've done the water pump, belts, rollers, fluid changes, vacuum lines. Overall it runs well but I've notice a tapping sound from the engine. Cant no longer hear it once the engine is warmed up, unless I'm at a stop next to other cars, or standing in front of it with the hood open. Car sat for 4 years before my ownership, I'm thinking it could either be a collapse lifter, exhaust leak or bent valve.

I decided to investigate further and purchased an automotive stethoscope and a engine compression gauge. Using the stethoscope I listed to each lifter. All lifters sounded identical except the very last one at the back, it had a loud metal tapping sound that matched the timing of the tapping sound I've been hearing from the engine.

Next I did a compression test. Cylinder 1 = 140 Cylinder 2 = 140 Cylinder 3 = 140 Cylinder 4 = 0

Most likely #8 valve is bent, or hopefully blown head gasket . I'm going to start disassembling the engine for further inspection. If the valve is indeed bent, I'll be replacing it along with all the seals, gaskets for both head and cam tower at minimum, if I don't find any other damage. Question is how far should I go with this rebuilt considering the engine only having 78k miles. Should I replace the springs, guides, anything else? I would like to do most of the work myself but would consider taking it to a machine shop for valve and head maintenance.

You might do a leak down test before pulling the head off, just to see how well the rings are sealing. Although if a valve is bent or not sealing at all, it may be hard to get a read on anything else going on in that cylinder. With that cylinder at TDC compression stroke, you could just put compressed air in the spark plug hole and see where it's coming out -- exhaust, intake, cooling system, or oil filler (most likely: exhaust valve, intake valve, head gasket, rings, respectively). If you have zero compression, it should be pretty obvious where the compression is going.

[rheidtman]

Yes, it surely sounds like a bent intake/exhaust valve. As long as the springs and guides measure properly, no need for replacement. A simple dial gauge will be your friend on the guides, while a carpenters square will verify spring height and straightness.

Rick
Oak Creek, WI

[libarra82]

Great! thanks. Getting up on Jack stand today to start disassembly.

I’m hoping it’s the head gasket. Oil pressure is good, no oil/coolant mixing, no white smoke from the exhaust. I did notice a puff sound along with the ticking coming from around that cylinder.

I’m in Vegas, I’ll start calling a few shops to see who can do the head maintenance.

[libarra82]

I don’t have a leak down gauge or air compressor, but could be worth the investment to confirm the piston rings are good.

[Tom]

I don’t have a leak down gauge or air compressor, but could be worth the investment to confirm the piston rights are good.

An air compressor is a must-have for any car guy. With zero compression, you can probably isolate where the compression is going without a fancy leak down gauge (that you are unlikely to use again anytime soon). I'd just quirt air in the spark plug hole at TDC (compression) and see where the air comes out...

Or, just pull the head -- chances are it will be obvious....

[barnwerks]

A 0 psi result from a dynamic compression test will generally have a visually obvious cause. It is very unlikely, however, that the cause is head gasket related. Keep in mind that the forces involved in bending a valve are often enough to also cause damage to other parts. The valve guide is the most likely collateral damage but the piston, connecting rod and rod bearing are also vulnerable.

[libarra82]

Got it torn down enough to check the timing, looks spot on.

Will stop here until the air compressor arrives to do the leak down, I’m sure I’ll find other uses for it

[libarra82]

Received the air compressor today. Shot air into the spark plug port and it all went out of the jboot, dang.

Odd that it was just that one valve, I would think cylinder one would be bent also, but that was good. Lifter on that valve is very chatty, maybe it too stiff and didn’t let the valve close all the way and hit the piston?

I’ll tear it all down this weekend to assess the damage.