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920 engine build waffle

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Re: 920 engine build waffle

Postby comnoz » Thu Nov 03, 2016 8:32 am

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


Not to worry. Between an engineer at ARP and myself -the maths have been done. :)
"If the facts don't fit the theory, change the facts." Einstein
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Re: 920 engine build waffle

Postby Fast Eddie » Thu Nov 03, 2016 8:39 am

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


Goodness gracious... you are quite right sir. It is indeed maths.

I shall go and stand in the corridor....

In my usual spot...!
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Re: 920 engine build waffle

Postby lcrken » Thu Nov 03, 2016 9:07 am

The "maths" for bolt design have been well known for a very long time now. This is not some new idea that we need to be nervous about. Waisted, or reduced shank, bolts would be a much more common design if it weren't for the fact that they cost more to produce. They are quite common in critical applications like high performance engines (head bolts, connecting rod bolts, main cap bolts, etc.), aerospace, nuclear energy, and so on. You can find the engineering data in any number of books and reference papers about the design and use of fasteners. Comnoz is not reinventing the wheel, just making good use of it.

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Re: 920 engine build waffle

Postby gtsun » Sat Nov 05, 2016 4:53 pm

Hey Jim I'm curious about the O rings you use in your 920 heads. My friend Wilson the Indian bike guy uses Viton O rings instead of base gaskets on them now and I'm curious what kind of O rings you're using. Are they silicon? It looks like a great idea and I'm tempted to ask you to do mine that way next time. Thanks, Glenn
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Re: 920 engine build waffle

Postby comnoz » Sat Nov 05, 2016 11:57 pm

gtsun wrote:Hey Jim I'm curious about the O rings you use in your 920 heads. My friend Wilson the Indian bike guy uses Viton O rings instead of base gaskets on them now and I'm curious what kind of O rings you're using. Are they silicon? It looks like a great idea and I'm tempted to ask you to do mine that way next time. Thanks, Glenn


I bought a supply of both viton and silicone.

The silicone handles a higher temperature. The viton has a little better chemical resistance.

KTM uses silicone o-rings at the head and I have reused them on my KTMs several times.

So far I have only run silicone on the Nortons with good results. Normal head temp on a Norton would be pretty close to viton's max temp.

I would probably choose viton for a cylinder base seal. Jim
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Re: 920 engine build waffle

Postby Fast Eddie » Thu Nov 10, 2016 10:51 pm

comnoz wrote:
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.

Image


Jim,

With your gasketless head seal trickery, what is stopping oil seep from the pushrod tunnels, to the cylinder head bolt holes, and out to freedom? It looks to me that an o ring around the pushrod holes would be needed... I know I'm wrong cos you've proved it works! So can you tell me what I am missing...?

In your first road test you did more miles than I'll do in a year! So are your trials with this set up are concluded? If so, are you going to offer kits? It would of course have been ideal for you to have modified my head to take the o rings whilst you had it, but we didn't know that at the time. Will you be willing to sell kits, along with clear machining instructions, so that folks like me on t'other side of the pond can use them?
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Re: 920 engine build waffle

Postby worntorn » Fri Nov 11, 2016 8:18 am

lcrken wrote:The "maths" for bolt design have been well known for a very long time now. This is not some new idea that we need to be nervous about. Waisted, or reduced shank, bolts would be a much more common design if it weren't for the fact that they cost more to produce. They are quite common in critical applications like high performance engines (head bolts, connecting rod bolts, main cap bolts, etc.), aerospace, nuclear energy, and so on. You can find the engineering data in any number of books and reference papers about the design and use of fasteners. Comnoz is not reinventing the wheel, just making good use of it.

Ken


+1
Phil Irving used waisted cylinder /cylinder head bolts in the series B and on Vincents (1947) . On a Vincent those 8 bolts attach the top of the engine to the crankcase and also hold the bike together.

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Re: 920 engine build waffle

Postby comnoz » Fri Nov 11, 2016 8:39 am

Fast Eddie wrote:Jim,

With your gasketless head seal trickery, what is stopping oil seep from the pushrod tunnels, to the cylinder head bolt holes, and out to freedom? It looks to me that an o ring around the pushrod holes would be needed... I know I'm wrong cos you've proved it works! So can you tell me what I am missing...?

In your first road test you did more miles than I'll do in a year! So are your trials with this set up are concluded? If so, are you going to offer kits? It would of course have been ideal for you to have modified my head to take the o rings whilst you had it, but we didn't know that at the time. Will you be willing to sell kits, along with clear machining instructions, so that folks like me on t'other side of the pond can use them?


I generally live with a new development for at least 12,000 miles before I start offering it as a proven service.
Up to that point I will do it with the understanding that it is still experimental.

I was prepared to relieve the 4 outer thick head bolt washers and use o-rings between the washer and head if needed. So far no oil has shown up around the head bolts.

When I installed the head I used a very light film of liquid Teflon sealant between the head and barrel. That may have provided the needed seal.

Also there is likely to be firm contact between the barrel and head in the area around the head bolts. That probably helps.

The o-rings are simply off the shelf rings and o-ring cord stock. .062 thickness.

The copper rings are just .040 magnet wire with carefully cut ends butted together.

Cutting the outside groove would be difficult without a CNC machine. Jim
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Re: 920 engine build waffle

Postby jseng1 » Sat Nov 12, 2016 6:14 pm

I'm surprised to hear that the silicone o rings work on the KTM heads. I've always wanted to try orings on the head but my experience with the hot running Norts is that pure silicone will deform and take a set over time. It loses it tension and starts to leak unless you can keep tightening it up every 6 months or so. The harder silicons such as 90 durometer seem to work better and last longer but I don't think the 90 hard is available in orings.

Hopefully it will won't leak after all that work.

See the deformed 70 hard silicone below.
Image

Even if the silicon does work - it only makes sense to oring the pushrod tunnels and the oil return. Why oring anything else??????
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Re: 920 engine build waffle

Postby Fast Eddie » Sun Nov 20, 2016 12:46 pm

Well, a bit of an update guys.

Here's the crank I bought for Steve a while ago, it was supposed to go in the current 850, but, well, you know how these things go:

Image

The crank now has a new home:

Image

Big holes in here:

Image

This is where the cNw / Comnoz reed valve breather will live

Image

How neat is this for a plugged timing case?! Still have to drill the extra hole below the pump, then its all 'modded' for the aforementioned breather:

Image

As I run an electronic tacho, I asked Steve to leave out the tacho drive machining ops. It means I don't need a cover for it, and (although its a negligible impact) the extra parent metal adds strength:

Image

Best described as having 'functional beauty' I think! I intend to get the cases and barrel tumble cleaned to match the head as done by sir Comnoz:

Image

Drive side machined to take stock primary chain cases. I shame to weaken them really, but I'm confident they'll still be plenty string enough for my needs:

Image

So, tumble cleaning and carbide coating for the bores are next in line for these:

Image

This is the head that Sir Comstock did for me earlier this year, it gave awesome results on the dyno and I intend to use it as is on the 920 build (with the squish band opened out to suit the 81mm bore of course) :

Image
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Re: 920 engine build waffle

Postby trident sam » Sun Nov 20, 2016 1:44 pm

Well, you never do things by half !
Is this motor for another chassis or for the blue Roadster ?
As usual , it looks fab :mrgreen:
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Re: 920 engine build waffle

Postby Fast Eddie » Sun Nov 20, 2016 2:20 pm

trident sam wrote:Well, you never do things by half !
Is this motor for another chassis or for the blue Roadster ?
As usual , it looks fab :mrgreen:
sam


It going in the Blue Bomber Sam. One day I'd like to put it, or similar, into a nice new build, lightweight Manx rep chassis. But that'll have to wait a bit...!
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Re: 920 engine build waffle

Postby gtsun » Sun Nov 20, 2016 3:25 pm

Well,,, before looking at these pictures I never thought of myself as being a purveyor of porn, but after staring at them I don't know what else you could call such pictures !!!
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Re: 920 engine build waffle

Postby baz » Sun Nov 20, 2016 4:05 pm

what a great looking/spec motor i'll be following this with great interest,brilliant stuff
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Re: 920 engine build waffle

Postby cjandme » Mon Nov 21, 2016 11:52 am

baz wrote:what a great looking/spec motor i'll be following this with great interest,brilliant stuff

Plus One here! :mrgreen: All I can say is - I gotta make more money.
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