1962 shortstroke 350 head spigot, gasket and bolt torque

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Peter Wright
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1962 shortstroke 350 head spigot, gasket and bolt torque

Post by Peter Wright »

I am working on a friend's 1962 short stroke model 16 Sceptre. After a bout of blown head gaskets it was fitted with a copper head gasket but it continued to blow. I have had the head off and determined that it wasn't flat. After some file work and testing with blue on a flat surface it is now pretty good and I consider an original style composition gasket and a bit of Loctite 510 should do the job.

Being a suspicious type I wondered whether the head might have been settling on the cylinder spigot rather than compressing the gasket adequately. I lightly bolted the head down and measured the gap between head and top of cylinder where the gasket goes using feeler gauges.

At its widest the gap is 36.7 thou. and the gasket itself measures as 34-37 thou. Clearly the head will bottom on the spigot without compressing the gasket and this is confirmed in the second photo where the gasket is shown slid into the gap up to the spigot.

Clearly the spigot recess in the head needs to be deepened. Does anyone know what the clearance here should be when fully assembled and tightened? I was thinking in the vicinity of 10 thou. (i.e. increase the depth by about 12 thou.). How much would the composition gasket be expected to squash when the head is tightened down? Obviously the compression of the earlier type copper gaskets would be negligible.

I am mystified by this because I don't think the small mount of metal removed to true the head could have created this deficit. To the right hand side of the cylinder the measured gap is 27.7 thou. which should work with the composition gasket. Prior to this exercise a copper gasket had been made and fitted and this was thick enough to ensure the head didn't bottom and the leakage was undoubtedly due to the uneven face.

And finally, what is the correct torque for the head sleeve bolts. The workshop manual (for 1957-64 models) says 40 foot-pounds for the scrambler and short stroke (page 78) and 35 for other models. This seems high and has caused crushing of the alloy under the sleeve nut heads. Or does the high figure assume some loss from settling of the composition gasket?

I hope someone can advise.

Regards,
Peter
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pkr87
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Re: 1962 shortstroke 350 head spigot, gasket and bolt torque

Post by pkr87 »

Many years ago I had a similar problem with my16M and I did not then have the facilities to machine the head or barrel, so I spent some time with grinding paste to make sure that the head would seal against the barrel and fitted the head without a gasket. It still works so I leave well alone. The head bolts I tightened with a ring spanner about 'that much'.
Peter Wright
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Re: 1962 shortstroke 350 head spigot, gasket and bolt torque

Post by Peter Wright »

I did give that notion a bit of thought but eventually decided that the Factory must know best, although I have to seriously wonder about this at times. Not so sure grinding in an alloy head would be the best idea but my vintage Ariel is done that way. And I always tightened it "that much" with a ring as well.

This particular head seems to be made of a particularly soft alloy and the pedestals under the head bolts had become quite dished along with the washers. On this engine, as well as the competition models the sleeve nuts to the through bolts mean there is less bearing area under the head than with a bolt so this issue becomes worse. When I took the head off I discovered the left rear was down to about 22 ft-pds. but this can't have affected it as it was actually blowing on the other side, between the pushrods. You will see on the photos that the pedestals have been milled down to tidy them up and extra thick washers made.

My next job is to find the composition head gasket that was on it previously and measure the thickness, to try and get an idea of how much these will settle in use so I can work out how much needs to be taken out of the spigot recess. I think the gap wants to be as small as possible.

Cheers,
Peter
pkr87
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Re: 1962 shortstroke 350 head spigot, gasket and bolt torque

Post by pkr87 »

I started by making sure that both the head and barrel had flat surfaces with straight edges and checking the spigot depth a Vernier gauge. It did not take a lot of work or grinding paste to make sure of a decent seal between the two by checking with Engineer's Blue. My engine is an all alloy trials unit with the sleeve nuts.
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GOLDSTAR
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Re: 1962 shortstroke 350 head spigot, gasket and bolt torque

Post by GOLDSTAR »

should there be gasket? I ask as the short stoke alloy comp engines were just 'lapped' in Kind regards
pkr87
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Re: 1962 shortstroke 350 head spigot, gasket and bolt torque

Post by pkr87 »

Goldstar, you might be right there. Mine is an earlier long stroke alloy engine which I originally put together from a box of bits in 1965. I did not have access to any spares supplier so made it up as I went along, using some bits from an ex army Matchless engine. After years of abuse, including some grass track racing the gudgeon pin escaped and tore a hole in the cylinder. The engine lay under my bench for 20 years till I found a genius who had a special sleeve made for it when I was able to rebuild the engine again, so I made it up as it had been before without a head gasket.Perhaps I got it right in the first place.Paul
Reynard24
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Re: 1962 shortstroke 350 head spigot, gasket and bolt torque

Post by Reynard24 »

The roadster short-stroke 350 (74mm and 72mm bore) engines do have a gasket - Steve Surbey supplies a copper gasket and the club supply a composite one both are listed as part no. 028100.
I've just measured a used spare copper gasket and it is 40 thou but there should also be two "O" rings (022518) fitted into the pushrod tunnel apertures on the gasket.
I torqued my 1963 350 short stroke sleeve nuts to 40ft/lbs and yes the alloy pillars do compress, it also happens on the long-stroke models.
Peter Wright
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Re: 1962 shortstroke 350 head spigot, gasket and bolt torque

Post by Peter Wright »

Thanks to all those who have commented, especially Raynard24 for confirming he uses a copper gasket and that the high torque is satisfactory/correct.

I had already resolved to use a copper gasket plus a bit of Loctite sealant but this so this confirmation is encouraging. This choice was mostly because of the greater thickness that will solve all clearance issues with the spigot. I measured a used composite gasket and it was down to .024" at the thinnest point and this squashing would need to be allowed for in estimating the metal to be removed to maintain some clearance if I were to continue with these.

I checked AMC Classic Spares site and the copper gasket listed there is noted "original spec.". Was copper indeed used for these late engines from new? I have several Payen gasket sets, some probably dating back to the 70s, and these all had the composite gasket. Probably an adequate material but thickness seems to be the issue, especially if any metal needs to be removed to true the joint.

A few issues still to resolve with the exhaust valve but hopefully I will gat to back to putting it together again early in the new year.

Thanks again.

Peter
Peter Wright
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Joined: Mon Jan 01, 1990 12:00 am
Location: NEW ZEALAND

Re: 1962 shortstroke 350 head spigot, gasket and bolt torque

Post by Peter Wright »

Don't know whether anyone will still be following this thread but thought I would provide an update. Obtained "original spec" copper gaskets but these are too thin. At 34 thou thick they will allow the head to bottom on the spigot, and are thinner than the 40 thou mentioned by Reynard24 further up this thread.

So that is the end of Plan D and I will revert to Plan A which is to use the copper gasket previously made by engineer friend. At 47 thou thick it will guarantee there will be no issues with the spigot. Naturally I should have done this in the first place and saved a heap of time and money. Hindsight is a wonderful thing!

If anyone else is going down this road I would strongly recommend they check their gaskets are sufficiently thick, be they copper or the composite type.

Cheers,
Peter
Steven S
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Re: 1962 shortstroke 350 head spigot, gasket and bolt torque

Post by Steven S »

I feel I must clear up a few inaccuracies in this thread. All short-stroke road models with alloy head and iron barrel were fitted with a copper head gasket, 028100 for the 350s and 030460 for the 500s (competition short-strokes with alloy head and barrel were lapped on). Composite gaskets were not fitted to these models by the factory and probably only supplied with aftermarket gasket sets because they were much cheaper to manufacture.

Our copper head gasket was copied from one in an original factory gasket set (red packet, Matchless logo, part numbered, first opened by myself), not a guess based on a composite pattern. This original, unused gasket measures 0.034" thick. I have other copper gaskets of the short-stroke type and they vary slightly in thickness: between 0.032" and 0.034".

Peter, as I have mentioned in our email conversations before, I suspect all is not right with your setup. The correct late 350cc short-stroke head (part number 028525) has a much deeper recess for the barrel spigot than other 350s. If measured with a ruler, I'd say it's about 7/32". However I have found discrepancies with this size in the past: one head measuring .209" recess and another .216". The easy way to identify a 1960s short-stroke 350 head is the larger 1 5/8" exhaust port.

Please remember that many of these bikes are worn and/or not standard. It is unfair to blame incorrect parts when in fact the bike itself may no longer conform to standard spec.

Steven Surbey
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