3 1/2 Litre, water in cyl. 6

Pekka

Corrajoints are hard to find. It also depends where the corrugations are in relationship to the new bigger bores.

Ok Ed,

I will have to measure the bores. And perhaps the compression volumes too, although it looks like only piston nr.1 showed signs of pinking. Otherwise I think she ran great with low octane ethanol free fuel and also good with 98E5, except for the leaks that then followed in the fuel system. But all of that should be cured now, so I should be able to run on 98E5 or V-power. :wink:

But in principle I think this should not be a huge issue, as isn’t it so that the oversize pistons available also produce a bore up to or even beyond 83mm?

+040" = 1.016mm and +060" = 1.524mm and those are the oversized pistons that are being delivered for engine rebuilds so surely there also have to be oversize head gaskets, right?

Hi,

So I measured the bores, yes, they are roughly 83mm.

The biggest measurements I got were close to 83.5mm although average was closer to 83.2mm and the smallest were very close to 83.0mm.

So i need to make sure the holes in the head gasket are also at least 83.0mm if not rather something like 83.3-83.5mm?

Cheers,

Pekka T. - 647194
Fin.

Hi Pekka, while making cylinder bore measurements you may wish to interpret the bore numbers beyond the topic of gasket size needed. Your numbers above have a range of 0.5 mm. In terms to compare with the shop manual, 1 mm is about 40 thousandths of an inch and 0.5 mm is about 20 thousandths, 0.020". The shop manual gives data on cylinder measurements (e.g., page B.37) and pistons (e.g., page B.42,43) with specifications down to the the ten thousandths inches level, 0.0001" level and tolerances that may be 0.002" or other levels at the few thousandths level or less, a factor of ten less than the 0.020" variation you mentioned.

Cylinder bores may have a lip at the top inside and may have longitudinal and transverse diameter variations which also may depend on how far down the bore the measurement is made. All of these measurements may be useful to help assess the condition of these parts of the engine while it is open so conveniently. Some of these blocks can be bored out larger than the factory shop manual specifications which may have been offered according to what spare parts supply the factory wished to produce. Custom pistons can be produced to almost any specification.

And what may have happened in the past is the traverse wear will be more on one side, so the re-borer ''moves " the bore slightly to that side, so that a smaller over size will fit . and so the bores may be a certain size but might not lineup with the gasket from memory gaskets are available in 83 a d 85 mm [ from MEMORY]

As long as you have the head off, you might want to measure the height to see if it has been shaved.
I measure one off a Z engine at 4.945 inches.

Hi all,

Thank you again for good advice. I am not very good at measuring and since the outer edge of the block is not machined, the distances are not so accurate, but I would say they are all within 1mm. Both surfaces look totally unchanged, which I think is odd if the block was bored anyways in the 1970’s.

I measured the head, the engine is a LHD MK IV 3 1/2 Litre engine, SL-prefix. The head is 125.5mm tall at the front and 125.4mm tall at the back. That is 4.9409" and 4.9370" so I don’t think it’s been planed or cut before.

I was thinking of having the machine shop only check for cracks and smooth the bottom surface by a minimal amount of sanding.

I asked Simon about the bore size on the composite gaskets, but so far only got the response that they are “standard size” and no other options available, except the copper only gasket.

Cheers,

Pekka T. - 647194
Fin.

Hi,

I got a response from Simon, telling me that the bore diameter in the composite head gaskets he has, is 83.5mm. :slight_smile: So I ordered a bunch of gaskets and parts worth £500 GBP plus shipping plus credit card charges amd also took the head for a light sanding/planing and crack testing. I hope next week I will be putting the head back where it belongs. :slight_smile: Oh BTW I took the valves out, they seem to be original, some still show the C479 or C480 stamping on the surface.

Cheers,

Pekka T. - 647194
Fin.

Hi all,

Ok, I should get the head back from the mill tomorrow and I will lap the valves and put everything back. I should also get the parts and head gasket from Simon via UPS tomorrow, 83.5mm bore holes and I hope they line up ok.

Should I use anything on the gasket? I guess no. The factory Service Manual of course speaks about using some stuff (sealant?) around the water passages, but I guess this was only due to the nature of the original Corrujoint gaskets, right?

How is it otherwise, I have had as a habit of putting antiseize on most fasteners, Locktite on some important ones, like carb linkage nuts and screws, and Blue Hylomar on all inlet, thermostat and other than exhaust manifold gaskets, incl. oil filter housing and oil sump gaskets (which I will renew and clean everything, so I should not have water anywhere in oil anymore).

For the exhaust manifolds I have NOT used anything. I could see when I took them out that I had had some blow by at both the head end and the downpipe flanges. Should I use some exhaust paste on those? So far I have only used such stuff on the metal-to-metal connections on my XJ6C, E-type etc. where some joints in the exhaust systems have the “olive” joints, or just a pipe that enters a flange.

So I take it all surfaces just should be smooth, clean and dry. Of course the threads and washers of the head studs should have light oil and be tightened in the correct sequence one 1/4 turn at a time. Lets see how this goes…

Cheers!

Pekka T. - 647194
Fin.

Dont forget valve/ rocker geometry, when shaving a pushrod head.

I have always used a spray, called CopprCoat, on metal gaskets. Not sure what the equivalent would be in Yurrup!

Pekka

The maker of those gaskets says a light spray of Hylomar on each side of the head.

Paul ,
When we were playing with the old 216 Chevies and 270 Jimmy’s some 50+ years ago no one worried about shimming the rocker arm stands, and the need was debated even then, unless the cut was well over .0625 and some of these heads, it was said, could be milled up to .187! No doubt someone probably did that no one in our circle of friends knew first hand of anyone that ever did.
Bob
889076
Plymouth, Mi.

Hi,

Thanks. I don’t think we have Hylomar available here in spray format, only in tubes.

Yes, I am using a modern composite gasket, if I was using copper or “Corrujoint” that might then be different, as the factory even suggested coating the surroundings of the water passages with something.

I think this is such a light shave (will need to measure once I get the head back later today) that just the normal adjusting of the rockers should be enough. One or two of the valves showed some signs of wear at the rocker end. If they are from the 1940’s that is not too surprising I think. Maybe there had been too big of a clearance at some time in the past.

Lets see how this goes once I have everything back in place.

Cheers,

Pekka T. - 647194
Fin.

Hi,

“Head”? I think you mean “gasket”? The other side of the head (top) always gets some blue hylomar as it has the rocker cover with a cork gasket.

Cheers,

Pekka T. - 647194
Fin.

I have used a copper spray head gasket sealant, but I don’t remember whether it was the Permatex 80697 or Loctite 37583 brand. These are intended for high temperature applications.

BTW a net search of Coppercoat and Koprkote yields other products.

Pekka

Sorry head ‘gasket’ The gasket maker recommends Hylomar , thin coat both sides …I personally would never usea cork gasket on alloy casting… a thin paper gasket with Permatex, or for the rocker cover , just a thin bead of silicon . It’s worthwhile with the rocker cover to lap it in on a piece of plate glass ad some valve grinding paste . After it’s been polished it could be not flat.

Pekka

The rockers can wear through the hardening against the valve stem … I’ve given up on originals and use MGB rockers the early ones . But this means elongating the holes in the head for the pushrods slightly , Making new pushrods [ easy and cheap] and new valv springs [ iskanderian] But does give 3/8" valve lift .
I can’t tell objectively how much improvement it makes as i did other things as well, but the combination with the other stuff was noticeable . That is noticeably better.

One just needs to be careful not to “over rotate” the rocker: it can stress the valve stem and guide.

Maybe overkill, but if I cut a pushrod head more than 0.020", I add corrective shims under the rocker stands (if applicable
.)

Easy peasy to correct on SBCs…:wink:

Never played much with the OHV V8’s and looking back no one worried about the change in valve stem “wipe” from either head milling or high lift cams. I mentioned 270 Jimmy’s in my first post and in these day’s of thin wall castings it’s hard to believe that we bored these engines 7/32 over size and the old 270 became a 4x4 302! Probably only Carl knows what I’m talking about, but a good Jimmy was equal to most Offy’s in sprint car racing in the early 50’s, quite an accomplishment for what started life as truck engine against a purpose built racing engine!
Bob
889076
Plymouth, Mi.