[30931]

On my 750 Spider Veloce I was losing coolant out the radiator overflow so I tried putting compressed air into each cylinder to see what happened. On cylinder number 4 coolant came bubbling out of the radiator.

I pulled the head and the head gasket fire ring, head and cylinder sealing surfaces all looked ok. I checked the liner protrusion and rather than .000-.002 cylinder protrusion above the block, I measure .003 below the block in one quarter of the circumference of the cylinder. I'm assuming this is the reason for the leakage.

Anyone know a cheap easy fix for this, or is the only answer to have the block machined?

Thanks,
Doug

 

[144]

Maybe the sealing ring at the cylinder bottom is bad. Did you remove the cylinder liner and check? Is there any coolant in the oil sump?

 

[otteud]

the height of the protrusion should be measured without the o ring for a correct measurement. the o ring is just a seal and when the liner is compressed it has no bearing on the liner height. measure the length of all the liners... are they the same , and if not see if there is a longer liner, next measure the block . hope this helps good luck!

 

[Gordon Raymond]

If the reason for the problem is one mismatched liner, the problem is easily solved. On the other hand if caused by a warp in the block, some machine work will be needed.
Is the head flat, not warped? If so, that's good. On early engines warped heads from overheating or burned exhaust valves will sometimes pull a warp into the block as well.
With the head off, and liner hold-down fixtures in place, will the crank turn easily? If it binds, the block may have a twist. This is also seen as just one badly worn main bearing.
Lets assume the block and head are straight, and you do not want to go to new liners and pistons. As mentioned, liner height needs to be measured with no sealing rings, clean liner flanges and clean block seats. You might wish to measure liner flange to top height to be sure you have one short one. You can determine how much short the liner is or how much the seat is low in the block. If you then buy a sheet of copper shim stock of the correct thickness, with only some difficulty, you can cut a shim washer that will fit between the liner flange and block seat.
I dry fit these initially, and tap the liner with a dead blow hammer to be sure my washer is compressed, and then re-reasure protrusion. If correct, the washer is carefully partly removed and glued to the liner flange, with a good flexible sealant like Permetex-Ultra Grey. The engine is then re-assembled with the "O" rings in place.
This will correct your problem. Lots of work, but if the head and block are not warped, and if you JUST have a short or mis-matched liner, this takes care of it permanently.

 

[intune]

Gordon's solution sounds correct. After blowing two head gaskets in my 750 race engine, we found #4 liner was short. Keith Goring has enough of a supply that he was able to find a taller one and have it machined to the correct specs. Working well, so far.

 

[Gordon Raymond]

The early sand cast 750 blocks are not the only place this happens. 101 1300's seem to have liners of varying heights as well. I don't know if this is a rebuild situation where a short liner gets fitted, or if the original "matched" liners were of different heights. The best solution at rebuild time, is to check head and block straightness, as well as liner protrusion. This is the time for adjustments, and the best solution is a too tall liner that can be cut to match the rest with NO shimming copper washers!

 

[30931]

Thanks all, for the replies.

Gordon, I was hoping someone would say that shimming the liner was an acceptable solution. Do you think there's any chance approaching it from the opposite end by gluing a shim on either the top of the liner or on the gasket fire ring could work? Obviously that's asking a lot more of the shim then for one on the bottom of the liner. I'm trying to keep this from snowballing into a complete rebuild.

As well as I can tell with a straight edge the head and block are straight. The liners were new and the protrusions were all in spec. eight years ago when I put it together.

Doug

 

[60sRacer]

Warning: Shela2525 is a spammer. Do not link to the garbage website; potential virus source.

Robert

 

[Gordon Raymond]

The liner can only be shimmed at the bottom. In theory, you could cut a stainless "O" ring grove in the liner top, and another in that cylinder, slightly offset from the liner grove, and the steel "O" rings would lock, and seal the fire ring in the gasket. This would be a total waste of time and money, as the machine work may as well be done on the entire head and four liners, at a cost of more than a new piston and liner set.

ALSO! Thanks Robert!