Lower cylinder wall rust through and sticking tappets!

[bondobob]

Hello all,

I've been slowly rebuilding my A4 and it's been quite frustrating. I did get it reassembled and test ran it, only to find I was getting water into 2 cylinders and that one of my valve tappets was sticking in it's hole. I'd had machine work done on the A4 and I know the machinist disassembled the valve train to replace a valve guide and knurl the rest of the guides. I'm wondering if they were sloppy and didn't return the tappets to their original bores. I've tried fitting the tappets into different bores but I'm finding that no matter what combination I try I've got 2 tappets that will not slide freely in ANY of the tappet bores! What gives?

I've also noticed pea sized rust spots on the lower cylinder walls below the piston bottom travel. I've cleaned them up with a scotch pad and oil but after a while (a week or so) they reappear, even though I leave the cylinder walls coated with oil. I've probed these rust areas with an ice pick and they seem solid, but the returning rust makes me wonder if these areas are porous and liable to leak cooling water into the cylinders (one of the problems I had with the engine that prompted a rebuild). I did find that my manifold bolts were really loose where they thread into the block and that's where the water may have also come from. I've fixed the manifold bolt threaded holes but I'm not sure if I'm now looking at having to sleeve my cylinders or get a new block.

Any advice on either of my engine problems would be greatly appreciated!

Thanks!

[hanleyclifford]

If the engine is still assembled you could try a pressure test of the cooling system. The head studs and manifold studs should have the threads in the block sealed with heavy Permatex or similar product or they can leak. Based on your description of the rust spots in the cylinders I am not optimistic. I have seen two engines recently with compromised cylinders below the piston travel area. This is a result of years of raw water blasting from the water jacket side. A good block will hold 20 PSI. The good news, however, is that the resleeving procedure on the A4 is simple and effective. Do not deal again with a machine shop that mixed up your valves or tappets.

[lat 64]

Hanley is right, the tappets should go back where they came from.
They should still slide freely though, even if they got mixed up.
This is one of the most precision parts of your engine—very close clearances.
A little nick or scratch can make them hang a little. Sometimes even old oil sludge sticks them. if you clean them up, they need to get polished. don't hit them with emery cloth. look for a dent on the edge of the tappets that stick. They might have got dropped.

That rust spot is disconcerting, but I don't have to tell you that.
A good machine shop will work with you maybe. It's kind-of their fault that they missed it, but kind-of not their fault because the block was bad. It's a tough call. You might as well be philosophical about it.

Russ

[67c&ccorv]

Originally Posted by bondobob

Hello all,

I've been slowly rebuilding my A4 and it's been quite frustrating. I did get it reassembled and test ran it, only to find I was getting water into 2 cylinders and that one of my valve tappets was sticking in it's hole. I'd had machine work done on the A4 and I know the machinist disassembled the valve train to replace a valve guide and knurl the rest of the guides. I'm wondering if they were sloppy and didn't return the tappets to their original bores. I've tried fitting the tappets into different bores but I'm finding that no matter what combination I try I've got 2 tappets that will not slide freely in ANY of the tappet bores! What gives?

I've also noticed pea sized rust spots on the lower cylinder walls below the piston bottom travel. I've cleaned them up with a scotch pad and oil but after a while (a week or so) they reappear, even though I leave the cylinder walls coated with oil. I've probed these rust areas with an ice pick and they seem solid, but the returning rust makes me wonder if these areas are porous and liable to leak cooling water into the cylinders (one of the problems I had with the engine that prompted a rebuild). I did find that my manifold bolts were really loose where they thread into the block and that's where the water may have also come from. I've fixed the manifold bolt threaded holes but I'm not sure if I'm now looking at having to sleeve my cylinders or get a new block.

Any advice on either of my engine problems would be greatly appreciated!

Thanks!

Valves guides are a press fit into the valve guide bore. When valve guides are pressed into the block the inside diameter of the guide is reduced and needs to be reamed to the correct I/D for the valve stem.

Cheers.

[bondobob]

Thanks everyone!

I think I'll go ahead and reassemble the engine to the point where I can do a pressure check. If it's bad news then I'll take it to a (different!) machine shop and see about sleeving the cylinders. I'll also have them check out my tappets and their bores to see what's up.

Thanks again for the advice, I was dithering on whether to take the block to a machine shop again or just put 'er together and hope for the best.... (you can probably tell I'm not the most patient home mechanic!)

Jeff