Sound advice please!

teazer said:
Plugs in that motor are long reach ie 3/4" but some plugs have projecting electrodes that protrude into the chamber. What the photos appear to show is a clear interference on one cylinder and a less dramatic one on the other.

In theory the interference would be the same both sides of the chamber on all 4 heads but the bores are probably not concentric.

I assume that your "mm" measurements are really Inches. ie 64mm bore in barrel and .045" gasket with 66mm bore.
Nope calipers where left on mm for all measurements. The.045mm was how thick the actual gasket is. Unfortunately works been non stop and I need to do a double tonight so I won't have till the 26 to get back to the motor and do the grease test

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.o45mm is .002" about as thin as a human hair and a 2.50mm bore is less than a 1/4" bore. I think maybe the calipers were on inches. :)
 
teazer said:
.o45mm is .002" about as thin as a human hair and a 2.50mm bore is less than a 1/4" bore. I think maybe the calipers were on inches. :)
You may be onto something. I'll double check if I ever make it back home!!

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teazer said:
.o45mm is .002" about as thin as a human hair and a 2.50mm bore is less than a 1/4" bore. I think maybe the calipers were on inches. :)
1.20MM thick
65.90mm gasket bore
63.75 mm cylinder bore

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That sounds closer, but the bore should be 64.0 if it's 3.0mm over. Unless the pistons are actually only 2.75mm over which is quite possible.
 
teazer said:
That sounds closer, but the bore should be 64.0 if it's 3.0mm over. Unless the pistons are actually only 2.75mm over which is quite possible.
The bore is a perfect fit, so the Pistons must be only 2.75 over.

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I think your best bet would be make some 'casts' of the combustion chambers using one of the 'setting' modelling clays available. That way you can compare shapes. Ten, either flycut heads or machine pistons. They are probably pretty thick on crown, doing minor machining won't affect piston strength
 
crazypj said:
I think your best bet would be make some 'casts' of the combustion chambers using one of the 'setting' modelling clays available. That way you can compare shapes. Ten, either flycut heads or machine pistons. They are probably pretty thick on crown, doing minor machining won't affect piston strength
Sounds good I'll pick some up tomorrow. You suggest covering the positions with a thin layer, torque everything down, then turn the motor over, renove the clay and let it harden? Still going to do the grease test also

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Probably use some silicon spray / polish first then a decent thickness of whatever left in position to harden, it may collapse if removed from combustion chamber. Use a dowel to block plug hole plus ordinary plasticene to radius off anything that could be 'undercut'. I've used a candle before now to drip wax into place ten smooth it our withfinger
 
I think at this point it would have been cheaper in money and effort to just get some new Wiseco or JE 836 pistons that fit the chamber out of the box. Those pistons are old and clunky.....the .003 skirt clearance says it all.
 
MR915 said:
I think at this point it would have been cheaper in money and effort to just get some new Wiseco or JE 836 pistons that fit the chamber out of the box. Those pistons are old and clunky.....the .003 skirt clearance says it all.
Wouldn't be against wiseco but there also not all that cheap. So far nothing after the rebuild has cost me anything but time and energy. Was hoping to be riding this summer.

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quadracer351 said:
Wouldn't be against wiseco but there also not all that cheap. So far nothing after the rebuild has cost me anything but time and energy. Was hoping to be riding this summer.


Then just put a thicker base gasket on and call it good. Worry about new pistons next season.
 
MR915 said:
I think at this point it would have been cheaper in money and effort to just get some new Wiseco or JE 836 pistons that fit the chamber out of the box. Those pistons are old and clunky.....the .003 skirt clearance says it all.

Forged pistons always need 'excess' clearace. Wiseco use up to 0.004"
I think Mahle are the only forged pistons that can use 'normal' clearance with their proprietary alloy (Porsche aided with
development)
 
crazypj said:
Forged pistons always need 'excess' clearace. Wiseco use up to 0.004"
I think Mahle are the only forged pistons that can use 'normal' clearance with their proprietary alloy (Porsche aided with
development)
Yeah I'm going to go with the slightly thicker gasket after checking for any damage and sanding the damage done in the head. I'd hate to change the profile of the domes if I'm going to end up with different Pistons in a year.

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I would still match combustion chambers and pistons. Machining would be minimal and you only need to change thickness of gasket if you fit different pistons. You know all 4 chambers are different so make the odd ones match then mke all te pistons the same (or, if you want to be clever, make left and right chambers and pistons depending on plug angles)
 
crazypj said:
Forged pistons always need 'excess' clearace. Wiseco use up to 0.004"
I think Mahle are the only forged pistons that can use 'normal' clearance with their proprietary alloy (Porsche aided with
development)
Don't know what Wiseco's run at .004 unless special application (nitrous etc). Wiseco CB750 836, 915 pistons @.002 and .0019 respectively. I run 72mm CB750 JE pistons down to .0013 in my billet block....your "normal" for cast pistons.
Those TRW pistons are close to 40 years old...like those old clunky, junky Arias and Venolia pieces from "back in the day". ::) :D
 
Wiseco supply a sheet with various clearances, I've never seen 'stock clearances used with any forged piston becuase the material they are made of expands more than the high silicon cast pistons. Mahle developed a really strong high silicon/low (ish) expansion material for forged pistons, afaik, Wiseco are not paying royalties to Mahle to use it? It's a very dark material, even when cut or machined. I've had a look at a lot of Wiseco pistons, the machining is way better since they started using CNC machines, (2007?) no longer have to get 3~4 sets of pistons to get one matching set.
 
MR915 said:
Don't know what Wiseco's run at .004 unless special application (nitrous etc). Wiseco CB750 836, 915 pistons @.002 and .0019 respectively. I run 72mm CB750 JE pistons down to .0013 in my billet block....your "normal" for cast pistons.
Those TRW pistons are close to 40 years old...like those old clunky, junky Arias and Venolia pieces from "back in the day". ::) :D
Would of loved the wiseco at the time I didn't have the money for them and these came up with a good price right during my engine rebuild. I'll be saving up and have them put on after riding for a little bit. Want to finally enjoy this bike!!!

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quadracer351 said:
Want to finally enjoy this bike!!!
Just have piston crown edges machined for clearance and use them. There is more than likely way too much material in there so lightening slightly will be a good thing
Here's a pic of DOHC pistons modified for SOHC
 

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