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920 engine build waffle

Classic Norton Commando Motorcycles.

Re: 920 engine build waffle

Postby comnoz » Tue Nov 01, 2016 8:15 am

Matchless wrote:On the subject of head gaskets, I wonder if Jim Comstock is any closer to having Cometic 920 head gaskets made. If he doesn't read this I'll send him a PM.


Cometic will only do them in copper without making a large investment for dies to make a multi-layer gasket.

I have been doing the cylinder head o-rings which have been working excellent. No gasket- no leaks.

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Re: 920 engine build waffle

Postby lcrken » Tue Nov 01, 2016 9:33 am

acotrel wrote:When you go to that big bore size, how do you seal the bit between the cylinders at the centre of the head, from leaking compression ?


Like Fast Eddie said, with a gasket. Or maybe now with comnoz's trick O-rings. That really is slick.

But for the old school methods, as you can see in this picture of a 920 cylinder, there is plenty of material between the bores for the head gasket to seal. I used the copper O-rings around the bores in addition to a copper gasket because this was a high compression engine. I've also run 920 engines without the copper rings, just the usual .040" copper gasket, with no problems. For race engines, I like the extra safety margin the O-rings provide.

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FWIW I don't recall ever having a head gasket fail on a Norton between the bores, but I have had them fail at the pushrod tunnels and at the outer edge of the bore.

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Re: 920 engine build waffle

Postby Fast Eddie » Tue Nov 01, 2016 9:52 am

I've got a couple of different thickness of copper head gaskets coming from JS so I can fiddle with squish gap. I don't intend to use anything on the barrel base apart from Wellseal. I intend to use the .005" copper wire loops around the pushrod tunnels and oil drain hole along with the copper head gasket.

I just have to decide what goo to use. JS swears by plybond. Matchless has an oil tight Maney 920 using BMW silicone sealant, 2 tubes of which I have on the shelf. And I have always had good results (but not used on the head/ barrel interface) with good old Wellseal. I don't want to be pissing around taking the head off to fix oil leaks...!
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Re: 920 engine build waffle

Postby B+Bogus » Tue Nov 01, 2016 10:17 am

No problems here using Welseal around the pushrods tunnel with a copper head gasket, but mine are just plain old wussy 850s....
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Re: 920 engine build waffle

Postby lcrken » Tue Nov 01, 2016 10:57 am

Fast Eddie wrote:I've got a couple of different thickness of copper head gaskets coming from JS so I can fiddle with squish gap. I don't intend to use anything on the barrel base apart from Wellseal. I intend to use the .005" copper wire loops around the pushrod tunnels and oil drain hole along with the copper head gasket.

I just have to decide what goo to use. JS swears by plybond. Matchless has an oil tight Maney 920 using BMW silicone sealant, 2 tubes of which I have on the shelf. And I have always had good results (but not used on the head/ barrel interface) with good old Wellseal. I don't want to be pissing around taking the head off to fix oil leaks...!


Yeah, we all have our favorite magic goo, don't we? Ron Wood turned me on to using Pliobond on copper head gaskests years ago, but I've also used pretty much every other goop there is at one time or another, from spray on aluminum paint to Yamabond. The latest 883 engine I did I used a copper head gasket with .005" wire set in Hylomar around the pushrod tunnels and oil drain hole (and it still weeps oil). They mostly all leaked some oil eventually. Jim Comstock suggested a high temperature pipe jointing compound, but I haven't had a chance to try that yet. The only engine I recall not having oil weeps was the stock 750 in my first Commando, a Production Racer that I only used stock flame ring gaskets in. Once I started modifying the engines for higher compression and bigger bores, I don't think I ever had one that didn't eventually start showing some oil around the head and cylinder fins at the joint. I think using a reed valve crankcase breather will probably help a lot, but I don't have any significant experience with that yet. Using Jim's waisted ARP head bolts should also help, but I don't have any experience with that yet either. Always something new to try.

I'm really intrigued by Jim Comstock's latest gasket free technique, and looking forward to seeing how it holds up to his high mileage riding.

So, is the gasket goo topic now up there with the infamous oil and tire threads on the list of perpetually repeating topics?

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Re: 920 engine build waffle

Postby Fast Eddie » Tue Nov 01, 2016 11:01 am

Well Ken, now you've mentioned wasted head bolts...

Did you get anywhere with the plan to get ARP to make ones for Maney barrels?

I'd love a set if you did !
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Re: 920 engine build waffle

Postby acotrel » Tue Nov 01, 2016 1:17 pm

Thanks for answering the question about the head gasket. I think that which ever way I go Jim Schmidt's long rods and light pistons will be essential to the exercise.
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Re: 920 engine build waffle

Postby Fast Eddie » Tue Nov 01, 2016 6:28 pm

Well, latest update is that a very large box has arrived at my house from Steve Maney containing the parts I mentioned in my initial post.

Frustratingly however, I am 5,000 miles away.

Did I mention that this is a tad frustrating?

Reminds me of being 6 years old and waiting for Christmas morning....
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Re: 920 engine build waffle

Postby lcrken » Tue Nov 01, 2016 6:33 pm

Fast Eddie wrote:Well Ken, now you've mentioned wasted head bolts...

Did you get anywhere with the plan to get ARP to make ones for Maney barrels?

I'd love a set if you did !


As a matter of fact, yes, sort of. ARP has their high strength stainless bolts available in the correct sizes for Maney barrels and heads, almost. The ones for the through bolts need to be shortened just a bit, but should work fine, and I think I'll have to turn down the diameter of the flange slightly on the through bolts. The Maney cylinders take the stock size through bolts, so they will work for either stock or Maney engines. The head bolts are for the Maney cylinders only, as they are 3/8-16 thread. I have two sets in hand, one with slightly shorter cylinder through bolts to fit the 75 mm stroke 750 I'm building for racing, which has shorter cylinders to use stock length rods, and the other for standard height cylinders. As soon as I've checked to be positive the through bolts will work (I know the head bolts are right), I plan to box them up and ship them off to Jim Comstock to do his CNC waisting magic on them. I don't have a price yet from Jim, but the machining process is pretty time consuming, so they probably won't be real cheap. I'll drop by ARP and pick up another set to include to Jim, and if you still want them when they are finished, you can have them at my cost. If not, I still have another couple of Maney engines to build, so I'd be happy to keep them for my own use.

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Re: 920 engine build waffle

Postby Fast Eddie » Tue Nov 01, 2016 8:40 pm

lcrken wrote:
Fast Eddie wrote:Well Ken, now you've mentioned wasted head bolts...

Did you get anywhere with the plan to get ARP to make ones for Maney barrels?

I'd love a set if you did !


As a matter of fact, yes, sort of. ARP has their high strength stainless bolts available in the correct sizes for Maney barrels and heads, almost. The ones for the through bolts need to be shortened just a bit, but should work fine, and I think I'll have to turn down the diameter of the flange slightly on the through bolts. The Maney cylinders take the stock size through bolts, so they will work for either stock or Maney engines. The head bolts are for the Maney cylinders only, as they are 3/8-16 thread. I have two sets in hand, one with slightly shorter cylinder through bolts to fit the 75 mm stroke 750 I'm building for racing, which has shorter cylinders to use stock length rods, and the other for standard height cylinders. As soon as I've checked to be positive the through bolts will work (I know the head bolts are right), I plan to box them up and ship them off to Jim Comstock to do his CNC waisting magic on them. I don't have a price yet from Jim, but the machining process is pretty time consuming, so they probably won't be real cheap. I'll drop by ARP and pick up another set to include to Jim, and if you still want them when they are finished, you can have them at my cost. If not, I still have another couple of Maney engines to build, so I'd be happy to keep them for my own use.

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Blimey, nice one Ken, you got that sorted pretty quickly!

YES PLEASE... I will definitely take a set Ken. Mine has a stock barrel height.

That's great to know this is sorted, its one of the thing that was on my mind to deal with, so thanks a lot!
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Re: 920 engine build waffle

Postby acotrel » Wed Nov 02, 2016 9:32 pm

How do you know the stretch will be right ?
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Re: 920 engine build waffle

Postby Fast Eddie » Wed Nov 02, 2016 9:40 pm

acotrel wrote:How do you know the stretch will be right ?


Cos Sir Comnoz has already done the math, and more importantly, the road trials.

If its good enough for his usage... its more than good enough for mine...!
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Re: 920 engine build waffle

Postby Matchless » Thu Nov 03, 2016 2:30 am

Nigel,

What has Jim already done ??

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Re: 920 engine build waffle

Postby Fast Eddie » Thu Nov 03, 2016 2:44 am

Matchless wrote:Nigel,

What has Jim already done ??


Tested the wasted head bolts.
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Re: 920 engine build waffle

Postby Matchless » Thu Nov 03, 2016 8:28 am

No, I was referring tongue in cheek to the math, or as we called it when I went to school, maths.

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