Valve Piston Clearance Bring Out the Clay!

swooshdave · Jul 19, 2019

Nothing hits. I’m calling it close enough.

baz · Jul 19, 2019

You need to cut through the centre of the clay and remove one half
Then you can measure the clearance
Cheers

Dances with Shrapnel · Jul 19, 2019

Get an exacto knife, cut some sections through the clay and measure the cut sections. Need certain clearance, not just hit no-hit assessment.

Dances with Shrapnel · Jul 19, 2019

And next time, pick a better colored clay.

acotrel · Jul 19, 2019

When you machine valve cutaways into a piston, that often makes them 'handed' left and right. Do Jim Scmidt's light 12 to 1 comp. pistons have valve cutaways ?

Fast Eddie · Jul 20, 2019

acotrel said:
When you machine valve cutaways into a piston, that often makes them 'handed' left and right. Do Jim Scmidt's light 12 to 1 comp. pistons have valve cutaways ?

Yes.

swooshdave · Jul 20, 2019

I was just checking to see if there was some gross error with the head. It was the one part that had been worked on by someone I didn’t know despite their excellent reputation. There was plenty of clay between the valve impression and the piston I didn’t bother to measure.

Too late now anyways.

SteveA · Jul 20, 2019

acotrel said:
When you machine valve cutaways into a piston, that often makes them 'handed' left and right. Do Jim Scmidt's light 12 to 1 comp. pistons have valve cutaways ?

You could always look at his website!

swooshdave · Jul 20, 2019

Dances with Shrapnel said:
And next time, pick a better colored clay.

Matched the bike.

acotrel · Jul 20, 2019

SteveA said:
You could always look at his website!

I have, but there is not even a photo of his high comp. pistons. In believe the crowns must be domed, but I would not know. He has got 12 to 1 listed for use with his long rods. It is the only way I can see of getting a real power boost for my 850. With 12 to 1 comp., methanol is even better. You could almost use that comp. with Elf racing fuel. You can play with cams all you like, but anything usually gives good power, just at different revs and with different exhaust systems. The law of diminishing returns applies. Jim's long rods and high comp. pistons would cost me about two grand. I think that would be money well spent.
If the pistons are 'handed' because of the valve cutaways, if you ding one with a valve, you can end up replacing them in pairs instead of just one at a time.

SteveA · Jul 20, 2019

acotrel said:
I have, but there is not even a photo of his high comp. pistons. In believe the crowns must be domed, but I would not know. He has got 12 to 1 listed for use with his long rods. It is the only way I can see of getting a real power boost for my 850. With 12 to 1 comp., methanol is even better. You could almost use that comp. with Elf racing fuel. You can play with cams all you like, but anything usually gives good power, just at different revs and with different exhaust systems. The law of diminishing returns applies. Jim's long rods and high comp. pistons would cost me about two grand. I think that would be money well spent.
If the pistons are 'handed' because of the valve cutaways, if you ding one with a valve, you can end up replacing them in pairs instead of just one at a time.

There is a picture Al! And like most pistons for twin cylinder motors, minimum quantity: 2....a pair....

https://jsmotorsport.com/product/norton-ultra-hi-compression-domed-piston-kit-racing-fuel/

https://jsmotorsport.com/js-motorsport-technical-pistons-and-rods/

acotrel · Jul 20, 2019

The first link is interesting. It shows the dome. It looks as though they can be used without the longer con-rods ? Or perhaps there are two lengths of piston available.
Thanks for that. If they can be used with standard rods, the price is not too bad.

acotrel · Jul 20, 2019

Just re-read the ad 'must be used with our longer rods'. So I would be talking about $2000 or such. I'll start buying lottery tickets again.

Fast Eddie · Jul 20, 2019

Al, all of Jim’s pistons require his long rods.

Those ultra high CR pistons would certainly make your methanol burner go well.

Until the crank broke and / or cases split...

Dances with Shrapnel · Jul 21, 2019

swooshdave said:
Nothing hits. I’m calling it close enough.

Had you considered the piston to cylinder head clearance in the quench area. The “clay” looks a tad tamped down around the RH intake valve quench area.

swooshdave · Jul 21, 2019

If it starts tapping when I get it running we'llknow one place to look!

Dances with Shrapnel · Jul 21, 2019

swooshdave said:
If it starts tapping when I get it running we'llknow one place to look!

“Once upon a midnight dreary”

swooshdave · Jul 21, 2019

It’s one of those things that is you use known stock components you shouldn’t have any surprises. Sure you can blueprint every engine you build but I’m not real good like on following blueprints.

acotrel · Jul 21, 2019

Fast Eddie said:
Al, all of Jim’s pistons require his long rods.

Those ultra high CR pistons would certainly make your methanol burger go well.

Until the crank broke and / or cases split...

Even if I don't increase the rev limit ? - I'm under the impression that the bottom end failures are usually due to over-revvig. !2 to 1 comp. is not ultra high. We have an880 JAP with is on 17 to 1, and a 600cc two-valve Jawa which is on 16 to 1. Methanol tends to save your motor. Petrol is a very nasty fuel to race with.

Fast Eddie · Jul 21, 2019

Dances with Shrapnel said:
Had you considered the piston to cylinder head clearance in the quench area. The “clay” looks a tad tamped down around the RH intake valve quench area.

That’s a good spot, it does look a tad thin.

Swoosh ‘should’ be correct however in that using standard parts, he should have adequate tolerances.

Fingers crossed !

Valve Piston Clearance Bring Out the Clay!

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