Engine rebuild questions

I have a 1965 4.2 block. The head is at Jag specialist being rebuilt, but I want to assemble the block myself. I know I want the machine shop to clean it, magnaflux it, and measure everything to make sure it’s good. What else?

Hone the cylinders?
Line bore it?
Polish the crank journals?
Machine the block to accept the rear main seal conversion?

It all depends on current condition. Is there internal corrosion on cylinder walls and the main bearing seats, etc

Line boring? NO! If you have the correct bearing caps in the correct order, you should be able to detect no mismatch across the joint between the caps and the block. If you do, you may have a boat anchor.

Cylinder honing? Yes. But the bores need to be assessed carefully to see if they are acceptable for condition and wear first. The ridge at the top must be removed too, if reboring is not required.

Polishing of the journals is called ‘linishing’ and again it depends on condition. If they are in top condition - no wear, no score marks or grooves etc, then this can be done.

The rear crank seal conversion? Others might be able to comment from experience but I run the original without any sign of a leak.


Line boring, no.
Honing yes of course!
Polishing crank, depends but probably not. Really depends on condition
Rear seal modification - no.

The crankshaft has to be cleaned out and a cleaned block needs to be cleaned again to make sure.
What else; have them check what they feel is necessary, and to be safe you should replace the conrod bolts and nuts.
Leave everything original as much as possible.

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Possibly might be good to inspect and take & record preliminary measure of the bores

That may allow you to formulate an initial plan

What the others have said, plus check the deck for flat yourself. You might want to do a very shallow pass just to make a nice surface for your new head gasket. Also look for “grading” letters adjacent to each bore. Each bore was matched to pistons using this system. If they’re still there it’s probably a “clean skin” block. If the deck and head have been machined before you might have to manage compression with the head gasket. Cometic make gaskets in various thicknesses to manage this issue. Also, if machining the deck make sure to provide the timing cover - need to machine as a “dowelled up” pair - otherwise the timing cover forms a step under the cylinder head. Ask your machine shop.

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I should have mentioned that the head, crank and connecting rods came from different engines. The original block had a badly corroded cylinder and 3 unusable pistons. The current block appears to be in really good condition including the bores. I can see an F on the deck and I have the bearing caps, but of course it needs new bearings and the crank came from a different engine.

I haven’t heard back from the guy doing the head, but when measured it was very flat and had not been machined before. It might get a skim pass.

Thanks for the reminder about the timing cover!

Hi, another item for the machine shop to perform is removing the crankshaft sludge plugs thoroughly cleaning the oil galley and install and peen new plugs.


My head was within tolerance, had no damages so of course I didn’t skim it. Why!

My block had a dent from me hammering pistons out so I chose to have it skimmed.

I mentioned cleaning the crankshaft and in my opinion it is really important.
New plugs are not required but an impact to get them out is a good idea.

Why no ? My mk 10 was done on the advice of the builder .

My shop said they broke a wrench getting those out, but did succeed. As to the rear main seal modification my very experienced shop with the XK engine did that with my engine overhaul and so far no leaks. I was reluctant with their prior XK engine experience to override their recommendation.

Because there are millions of engines with rope seals that work rather well and turning the crank down is a big change in my opinion, just to fit a rubber seal that might lose a little bit less oil - of course I‘m happy for you if it works well.

In one video I watched…when the rear seal “assembly” was bolted back onto the block they put a thin film of sealent around the entire circle where the parts met…Never heard of this before but seems like a simple way to help prevent an oil leak.

I was getting ready to take this to the shop and your comment about the timing cover came to mind. I have a lot of mismatched parts. The block is from one car, the timing cover from another and the head from another. How might that affect the timing cover-to-head mating? I have the block that goes to the timing cover, but it’s going to need 1-3 cylinder sleeves.

Bolt it up and feel for a step… it must be machined flush, that’s all.

Cover and block were stamped by the factory if you want to know if they were matched originally

I used a half inch drive impact gun with a one-piece Allen socket. I tried all the plugs lightly until the all the easy ones came out. Then I heated the tough ones with a o.a. torch with a very small tip. Once the plug gets red hot, I let it cool back to blue and hit it with the impact again. Then they come right out. Then I would cool the area of the crank with air. It doesn’t have time to get very hot anyway. You will be surprised at the amount of crud behind the plugs.

Be sure not to use chrome rings, only cast iron.

Chrome should really be used only in new, properly-honed bores.

What you say is true, but the issue is getting a good quality rope seal today. New rope seals are too long and different in consistency - they simply do not fit and would have to be cut to length. This is from my recent experience in rebuilding a couple of engines. Even with the special seating tool, it was impossible to place the seal. If you could find nos, yes, I would prefer that. If your seal is too long, it will overheat and fail. If too short, it will leak. What used to be a straight-forward operation is now guesswork. If someone has a source for good rope seals, I would like to know about it.

There are two seal kits, and I’ve placed the 1 piece myself, had a machine shop do a two piece. The experienced machine shop much prefers the two piece Bill Terry one, and I don’t disagree. The one piece is an old style seal cut at one edge requiring removal and replacement of the seal spring, while the two piece seal is standard Cadillac lip seal of modern style without spring. The cut of the crank is greater for the 2-piece.