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Vintage piston? Mike Corey 12-13-2007
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Posted by Mike Corey on December 13, 2007, 9:23 pm
I'm having a 1975 Honda XL350 engine completely redone. I mean
everything. Every seal, gasket, bearing and bushing replaced if it needs
it or not. New valves, valve seals, guides, piston and rings. You name
it, if it even looks worn, it's getting replaced. I'm doing the search
for NOS or aftermarket parts myself, to save paying the mechanic for
surfing the net for them.

I believe I've found everything but a piston. The OEM piston is 79mm
with a 8.3 to 1 compression ratio. The engine currently has a 79.5mm
piston. I want to bore it to a 81mm with 9.5 to 1 ratio. I called JE
Pistons, and they don't have the specs on file needed to make me a
piston. The best they can do is if I send them an old piston, along with
the combustion chamber volume, then they can make one. I have no idea
what the combustion chamber volume even is!

Are there any other piston companies out there that can make me a piston
like I want, by me just saying the make / model / year and size of
piston? Wiseco maybe?

TIA


Posted by J. Clarke on December 13, 2007, 11:13 pm
Mike Corey wrote:
> I'm having a 1975 Honda XL350 engine completely redone. I mean
> everything. Every seal, gasket, bearing and bushing replaced if it
> needs it or not. New valves, valve seals, guides, piston and rings.
> You name it, if it even looks worn, it's getting replaced. I'm doing
> the search for NOS or aftermarket parts myself, to save paying the
> mechanic for surfing the net for them.
>
> I believe I've found everything but a piston. The OEM piston is 79mm
> with a 8.3 to 1 compression ratio. The engine currently has a 79.5mm
> piston. I want to bore it to a 81mm with 9.5 to 1 ratio. I called JE
> Pistons, and they don't have the specs on file needed to make me a
> piston. The best they can do is if I send them an old piston, along
> with the combustion chamber volume, then they can make one. I have
> no
> idea what the combustion chamber volume even is!

Pull the head, cover the combustion chamber with a plastic plate with
a hole in it, use a burette to fill the chamber with water or oil or
whatever you like, when it's full read off how much you've used and
you've got the combustion chamber volume.

> Are there any other piston companies out there that can make me a
> piston like I want, by me just saying the make / model / year and
> size of piston? Wiseco maybe?
>
> TIA

--
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)



Posted by Dave Emerson on December 14, 2007, 8:52 am
Bruce Richmond wrote:

>
>>Mike Corey wrote:
>>
>>>I'm having a 1975 Honda XL350 engine completely redone. I mean
>>>everything. Every seal, gasket, bearing and bushing replaced if it needs
>>>it or not. New valves, valve seals, guides, piston and rings. You name
>>>it, if it even looks worn, it's getting replaced. I'm doing the search
>>>for NOS or aftermarket parts myself, to save paying the mechanic for
>>>surfing the net for them.
>>
>>>I believe I've found everything but a piston. The OEM piston is 79mm
>>>with a 8.3 to 1 compression ratio. The engine currently has a 79.5mm
>>>piston. I want to bore it to a 81mm with 9.5 to 1 ratio. I called JE
>>>Pistons, and they don't have the specs on file needed to make me a
>>>piston. The best they can do is if I send them an old piston, along with
>>>the combustion chamber volume, then they can make one. I have no idea
>>>what the combustion chamber volume even is!
>>
>>It's "X"
>>Andhttp://www.cyclechaos.com/wiki/Honda_XL350#1975says the
>>displacement is 348cc
>>
>>(348 + X)/X = 8.3
>>348 + X = 8.3X
>>348 = 8.3X - X
>>348 = (8.3 - 1)X
>>348 = 7.3X
>>X = 47.67
>>
>>
>>
>>
>>>Are there any other piston companies out there that can make me a piston
>>>like I want, by me just saying the make / model / year and size of
>>>piston? Wiseco maybe?
>>
>>>TIA- Hide quoted text -
>>
>>- Show quoted text -
>
>
> That assumes the 8.3 is accurate. It also assumes that the piston has
> a flat top that is flush with the top of the cylinder. The chamber
> could be larger and part of it is occupied by a piston dome. The deck
> height is probably a bit below the top of the cylinder and there are
> valve pockets in the piston crown that figure into the combustion
> chamber volume.

Actually... Honda already considered their piston's crown when they
came up with their compression ratio. Right? If the numbers 8.3 and 348
can be trusted, the calculated volume should be correct.

Mike Corey ought to tell JE Pistons exactly *how* he arrived at whatever
volume he sends them.

Posted by Mark Olson on December 14, 2007, 10:17 am
Dave Emerson wrote:

>>Pull the head, cover the combustion chamber with a plastic plate with
>>a hole in it, use a burette to fill the chamber with water or oil or
>>whatever you like, when it's full read off how much you've used and
>>you've got the combustion chamber volume.

> That's only a practical approach if the engine is complete.
>
> My reading of the OP is that the engine is already dismantled.

Yes...

How can you cover up the combustion chamber with a plastic plate
if engine isn't dismantled, at least the cylinder head has to be
pulled off the engine, right?

There seems to be some confusion here, some people are trying to
measure the cylinder head combustion chamber volume alone, others
are trying to point out the piston may or may not have a flat top
and it may not come up to the top of the bore, etc.

For the OP's purposes, measuring the CC volume with the plastic
plate approach, plus sending the piston to the fabricators, should
be sufficient.

--
'01 SV650SK1 '99 EX250-F13 '98 ZG1000-A13
OMF #7

Posted by J. Clarke on December 14, 2007, 12:55 pm
Dave Emerson wrote:
>> Mike Corey wrote:
>>> I'm having a 1975 Honda XL350 engine completely redone. I mean
>>> everything. Every seal, gasket, bearing and bushing replaced if it
>>> needs it or not. New valves, valve seals, guides, piston and
>>> rings.
>>> You name it, if it even looks worn, it's getting replaced. I'm
>>> doing
>>> the search for NOS or aftermarket parts myself, to save paying the
>>> mechanic for surfing the net for them.
>>>
>>> I believe I've found everything but a piston. The OEM piston is
>>> 79mm
>>> with a 8.3 to 1 compression ratio. The engine currently has a
>>> 79.5mm
>>> piston. I want to bore it to a 81mm with 9.5 to 1 ratio. I called
>>> JE
>>> Pistons, and they don't have the specs on file needed to make me a
>>> piston. The best they can do is if I send them an old piston,
>>> along
>>> with the combustion chamber volume, then they can make one. I have
>>> no
>>> idea what the combustion chamber volume even is!
>>
>> Pull the head, cover the combustion chamber with a plastic plate
>> with
>> a hole in it, use a burette to fill the chamber with water or oil
>> or
>> whatever you like, when it's full read off how much you've used and
>> you've got the combustion chamber volume.
>>
>
> That's only a practical approach if the engine is complete.
>
> My reading of the OP is that the engine is already dismantled.

If he's already got the engine dismantled then it's even easier since
he doesn't have to pull the head.

Here's a more detailed description of the procedure.
<ttp://www.hydrostream.org/ArticleArchives/CCHeads.htm>



--
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)



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