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MG TD TF 1500 - Cylinder Head Cracks

I was looking over the cylinder head of my TD/C engine carefully before assembling it, and found valve guide boss cracks. Very disappointing.

The car is TD/C7254 with a head casting number of 22952 -- the original cylinder head. It looks like only the exhaust bosses at each end of the head have been spared.

What hope is there that these cracks can be repaired?
Who might be able to do this type of work?

I've not had success with repaired head cracks, and so i'm thinking I'm going to have to replace the head. If so, is it important to find another with the oval/banana holes to match the block?



Charlie Adams

Here is the second pair of intake valve guide bosses.

Charlie

Charlie Adams

Those look like really tough cracks to repair. Stitching is probably not an option so they would have to be welded and machined. Sadly, the head may be scrap. That said, and never having seen that type of crack before, I wonder if it's really a problem. Maybe someone forced some slightly oversized guides in there?

I probably have a spare round hole head here if you can't find one locally.
Steve Simmons

Charlie,

I've never owned a T-series, so take this with a grain of salt. But, when porting an MGB head, it is pretty common to grind that lug out of the head. So, if the crack does not extend too far, maybe that could save your head?

Charley

C R Huff

Remember, different metals have different coefficients of expansion. If a metal with a higher coefficient of expansion was used sometime on the valve guides, under heat it could expand more than the cast iron head and cause cracking.

I have heard of this happening with silicon bronze guides. My machinist will use nothing but cast iron valve guides.
Lew Palmer

I have seen a couple of XPAG heads where all the bosses in the ports had been ground away, as Charley Huff suggests - so that solution is not unknown. I don't know if the work was done primarily to aid gas flow, or to remove cracks, but it could solve your problem, and better than scrapping the head. Obviously the valve guides would need removing to do the work, probably with a rotary burr on a flexible drive, and the dividers in the inlet ports could be gas flowed at the same time. You should also get an improvement in acceleration.
R WILSON

Sounds like a sensible solution Ray if sufficient support remains for the guides. I think the biggest danger if left alone would be from pieces breaking off and ending up you know where.... I am sure there are far more experienced hands than I who could comment on that.
Chris
C I Twidle

I think the biggest concern would be the cracks propagating and providing a leak path. Removing the guides and grinding back appears to make the most sense, providing sufficient support remains. But agree more expert advice required.
Dave H
Dave Hill

I'd just leave them alone as I don't see them propagating up into the thicker meat. Grinding the iron away on exhaust ports will expose more valve stem to hot exhaust where it should be conducting heat to the iron.

No telling how long ago the issue started. Go back and look at them 20 years from now and they'll look exactly like they do now.
JIM N

Thanks for your comments!

Since my original post, I've contacted 4 shops which do some head welding repair which add to the discussion.

Tim Hadley of Midwest Cylinder Head and Machine said he would be fairly confident in running the head the way it is. Leo Croisetiere of R&L Engines said he doubts these cracks will go further and that the head is usable. He suggested installing bronze guides which have a small lip at the head top to assure no guide migrates. Ralph Picarello of The Restoration Shop he would consider drilling small holes at the base of each crack to preclude the cracks from extending further.

I'm intrigued with the idea raised by Charley of grinding the bosses back to below the area where the cracks begin. As long as there is enough meat to hold the guides, this step seems sensible since it will improve flow and eliminate the cracks.

This head now measures 2.928 in/74.37mm, and my engine has 0.040 over pistons.
Charlie Adams

Charlie,

With respect to the bosses being able to carry the guide after grinding the bosses down, I suspect that the cracked part of the boss isn't adding any "holding power" to the guide anyway.

I would rather have the damaged part out of there since it might come apart, which would be bad news on the intake side.

I don't know how much depth of the guide hole is left after grinding the hump out of your head, but grinding that section out is done on A and B series engines (MGB & Sprite). I have done one of each.

Charley
C R Huff

This thread was discussed between 31/03/2018 and 10/04/2018

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