New block

[Andy Bennett]

I have made a somewhat speculative purchase of a block and would appreciate some guidance on what my options are.

With my engine chewing a head gasket once a year (1000 miles) due to various breaks across the gasket caused i suspect by less than perfect surfaces on the block/head, and there being a lot of exhaust fumes from the tappet cover (with cord rings having been fitted by a previous owner to ‘cure it’) I have for some time been planning a top end upgrade/rebuild/repair.

Well, the opportunity has come to fruition. I have purchased a block with the following identification: 7521, 31 8 29. Now call me Sherlock, but I take it from this that it is a 1929 block.

My box is a 1933 model.

The block at first look appears basically sound. It needs some helicoils etc and some surface refinishing, but hopefully nothing too problematic from what I can see so far.

So to my questions:

The bore sizes are 2.235 to 2.237 inches. Is it safe to take it that this means that it has been bored to +30, rather than +40?

The block is ‘naked’ so no guides, valves, studs etc. I cannot see any significant changes from the 1929 to 1933 block design, so can I use this 1929 block on my 1933 engine? If so should I use the earlier flanged guide etc as on the pre 31 engines or can I just use the later plain guide etc in this block and so basically build it up as a 1933 spec block?

One of the water inlet manifold stud threads has suffered somewhat, as in below picture. Clearly this is going to be an area which suffers from corrosion. However, it also doesn’t take pressure. There doesn’t look like a great deal of material to take a helicoil and there is a decent amount of thread present, so recommendations appreciated, should I just use as is or attempt helicoil?
edit: there is more material than the close up image suggests, the shadow makes it look worse than it is.

Thanks all

Andy

[Nigel was in Brittany]

Willie McKenzie does an adaptor that needs 4 holes drilling/tapping to overcome the problem with the side water take off.

[Andy Bennett]

Willie McKenzie does an adaptor that needs 4 holes drilling/tapping to overcome the problem with the side water take off.

Ah yes thanks, I take it that it bolts to the block via the new threaded holes and provides a fresh thread for the manifold stud to screw into.

Andy

[bystander]

A 1929 block will fit a 1933 crankcase, but there are a few differences. Flanged valve guides are a smaller od than the straight type, so not interchangeable. The valve chest cover is not interchangeable as the fixings are in a different position. The core plugs are probably the earlier screw-in type, not knock-in as in 1933. None of these things are a problem, save for originality's sake.Looking at your photos, you might simply get away with tapping the water branch fixings to 3/8 bsf and using stepped studs (the usual suppliers will probably have these - stepped head studs would do). If the bores are really 2.235/7, you will probably need to re-bore and you should check if liners have been fitted previously - may not be advisable to bore these any larger.

[Hedd Jones]

And with respect to bore size. Yes +30. Select pistons by recommended bore OD

[Andy Bennett]

Thanks all for quick replies.
There definitely aren't any liners and the bores look good with no scoring or marks.

Core plugs are screw in, with large 'screw head' across them. Should I unscrew these, as I of course don't know if they are leak tight, and if so should I reseal threads with blue hylomar or is there a special sealant/gasket?

And to clarify, I will need the flanged valve guides, but then I fit collet style valves?

thanks again
Andy

[bystander]

Thanks all for quick replies.
There definitely aren't any liners and the bores look good with no scoring or marks.

Core plugs are screw in, with large 'screw head' across them. Should I unscrew these, as I of course don't know if they are leak tight, and if so should I reseal threads with blue hylomar or is there a special sealant/gasket?

And to clarify, I will need the flanged valve guides, but then I fit collet style valves?

thanks again
Andy

If the core plugs look ok I would leave them alone, they are unlikely to leak if they haven't been disturbed, and would probably be a real b*gger to undo (although saying that, it might be worth taking them out to clean out any accumulated crud in the block). No problem with valves, all types are the same stem dia. (apart from the Reliant replacements that were around a few years ago) and are all interchangeable using the appropriate fixings.

[Andy Bennett]

Thank you 'bystander' I have the confidence to go forward with it now in knowledge that it will be OK for me to use.

[Chris KC]

While you're at this stage Andy it's well worth having a gentle poke about inside the water jacket with a bit of stiff wire to dislodge as much crud/ limescale / loose rust as you can. And before skimming the faces just check how deep the block is...

[Andy Bennett]

While you're at this stage Andy it's well worth having a gentle poke about inside the water jacket with a bit of stiff wire to dislodge as much crud/ limescale / loose rust as you can. And before skimming the faces just check how deep the block is...

Thanks Chris
Yes I have already dislodged a few large scales from the outside of the cylinders and wonder what else is lurking inside. Perhaps I will try to remove the screw on core plugs to make a complete job of it.

I hadn't thought abut the block height, presumably to avoid the pistons going above the height of the block. Do you know the minimum height I need as I have done quick search and cannot see anywhere.

cheers
Andy