Vintage piston?

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

 

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 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.

 

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.

 

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>

 

Did you not read where he said " if I send them an old piston, along with

I am making some devices for Lotus guys that are a polycarbonate dish that
fits the piston to "cc" the volume of the piston crown. I am certain that JE
Pistons has one.

 

You might be able to get a mold of the combustion chamber
without too much trouble. You could perhaps line the head
with a plastic such as saran wrap, then use an epoxy putty
to fill the cavity and shave the epoxy off flush with the surface
of the head.

If this worked, you could send the mold along with the old piston.

One note of caution: I have never tried this, but I'd consider it
if I had a similar problem. Epoxy puttys are pretty easy to use
and ought to do the job nicely. Maybe $5-$10 for the putty in
an auto parts store. Bondo might work too.

 

Geez, just take it down to the high school auto shop and say "anybody
here know how to cc (prounounced "see see") a head?"

 

How would you figure valve the cutouts ?

 

You drop the valves in and if necessary hold them with your fingers.

 

Wow, you make me feel so special

With the piston at TDC use a set of parallels and a depth mic to
determine the height of the dome above the deck. Replace the top ring
with a rubber o-ring and push the piston down below the deck. Depth
mic from the deck down to the top of the piston and calculate how far
it is below TDC. Using the same equipment you used to cc the head,
measure the volume above the piston to the deck. Calculate the volume
displaced by moving the piston down from TDC. Subtract the measured
volume. The result is the volume of the dome with all it's
irrgularities that must be subtracted from the head volume to get the
actual combustion chamber volume.

Bruce

 

Forgot to mention, add the additional volume caused by using a head
gasket to your combustion chamber volume.

For the true compression ratio add the combustion chamber volume to
the cylinder displacement and divide the total by the combustion
chamber volume.

 

***********************************************************

Honda still produces the 1mm overbore piston for that bike.
Here is one on Ebay Canada
http://cgi.ebay.ca/Honda-XL350-Pist...0837351QQihZ014QQcategoryZ10066QQcmdZViewItem

What is the number on the top of your piston?


Wudsracer/Jim Cook
Smackover Racing
'06 Gas Gas DE300
'82 Husqvarna XC250
Team LAGNAF

 

Why don't you just bore it to 1 MM over and use the $66 pistons from
ServiceHonda.com?

 

Here they are,
http://i221.photobucket.com/albums/dd236/arborigine/MVC-085S.jpg
http://i221.photobucket.com/albums/dd236/arborigine/MVC-082S.jpg

Drip fluid in from a burette and subtract amount from empty volume.

 

Will the fluid from a blonde or redhead work just as well?


Oh, sorry, I was reading too fast...

--
"Outback" Jon - KC2BNE

AMD Opteron 146 (@2.8) and 6.1 GHz of other AMD power...
http://folding.stanford.edu - got folding? Team 53560

2006 ZG1000A Concours "Blueline" COG# 7385 CDA# 0157
1980 CB750F SuperSport <== For Sale $1200

 

Mike Corey needs parts:

OK. Coming in late to this but two ideas.

1. Ebay. That's where I got almost everything to build my C&J frame
XL341 motocrosser. You should be able to find something. Don't
forget
that, if it's AHRMA rules, it's 350 *plus* maximum allowable overbore
(0.080")

2. You're in Iowa flat tracking? Who's the guy that builds
electronic
ignitions for XL/XR flat trackers, he's from those parts. He should
know. If you don't know him, email me at mikesturdevant127
at
hotmail
dot com
and I'll find his number for you. As I say, he's local to you and he
should be able to help.


Go fast. Take chances.
Mike S.

 

That would be Pat Orman. I bought his electronic ignition four years
ago. They work fantastic. I e-mailed Pat a few days ago about a piston,
and he just replied today. He's working on one for me, but won't have
any until the end of January. Which is fine, I'm in no big hurry.

Thanks to all that replied.


"War is an ugly thing, but not the ugliest of things; the decayed and
degraded state of moral and patriotic feeling which thinks nothing is
worth a war, is worse." --- John Stuart Mill: