All Things CR250

Bernie Adamson · Joined: 20 Jun 2003 Posts: 3001

Ian,

Ian Harrison · Posted: Sat Apr 19, 2008 6:05 am Post subject:

deleted, double posting disease. Ian
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Ian Harrison
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Championship winning Superkart race team 1997-2012

Ian Harrison · Posted: Sat Apr 19, 2008 6:48 am Post subject:

Bernie, My lips are sealed, but check your mail

Ian
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Ian Harrison
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sales@viper-racinguk.co.uk
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Championship winning Superkart race team 1997-2012

Sam Zavaglia · Posted: Sun Apr 20, 2008 4:04 pm Post subject:

Is this open to a guessing competition or do we all check our email? Laughing

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Chuck Bunnell · Posted: Sun Apr 20, 2008 6:40 pm Post subject:

Not to get back on topic, but for an O-ring sealed head, what material is used for the washer under the acorn nuts on the head? Brass or copper?

Ian Harrison · Posted: Mon Apr 21, 2008 12:03 am Post subject:

Hi Chuck

Yes I didn't want to reply to Sam as it was "drifting", but Sam guess all you like (just not on this thread Laughing

) . Only me and Bernard know the truth for sure!!

Now then:

We use brass with stainless steel acorn nuts. Acorn nuts are taller than domed nuts allowing for the protruding stud length without bottoming out (as Chuck obviously already knows).

Brass washers are more durable than copper, which tend to squash and spread gripping the stud threads and making them difficult to remove, brass also looks nicer Cool

!!

You may sometimes (rarely) get a slight weeping with brass washers until they have gone through a running/heat cycle. Don't worry they will seal on their own and never seem to weep again even when removed and re-used.

Best Regards

Ian Harrison Very Happy

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Ian Harrison
Viper Racing UK
www.viper-racinguk.co.uk
sales@viper-racinguk.co.uk
+44 7984 225 564
+44 161 343 2009
Championship winning Superkart race team 1997-2012

Erik Frank · Posted: Mon Apr 21, 2008 9:12 am Post subject:

Here's the hot setup:

Yamaha YZ-125 domed acorn nuts (high dome with nice wide flange at the base)

Suzuki "thick" copper washers....probably .060" (1.5mm for Ian) thick and made from a harder copper so they don't wear out as fast.

I'll have to dig for the part numbers, but this is what I used as my preferred setup.

-erik
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Andy Kiker · Posted: Mon Apr 21, 2008 11:08 am Post subject:

I agree with Erik on this. Yamaha acorns and suzuki copper works best.
Also works well on brand X with this topic. Very Happy

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Ian Harrison · Posted: Mon Apr 21, 2008 5:03 pm Post subject:

Hi Guys

My nuts and washers will look great long after yours are dull and tarnished Cool

But to show there's no hard feelings:

Yamaha YZ125 Flanged Acorn Nuts - Pt.#. 90176-08026-00 - $3.01 Each
Suzuki Head Nut Washers 8.5 x 17 x 2mm Pt.#. 09168-08021 - $1.22 Each

That's $25.38 the set. Boy you guys have money to burn!!

Can't find any 1.5mm thick Erik, but these seem to be listed for all M/X bikes.

Mine also give an extra 2hp and 400 rpm Confused

e-x-c-e-p-t when used on brand X. Then gives 5HP and 1,000rpm less Laughing

Regards

Ian Very Happy

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Ian Harrison
Viper Racing UK
www.viper-racinguk.co.uk
sales@viper-racinguk.co.uk
+44 7984 225 564
+44 161 343 2009
Championship winning Superkart race team 1997-2012

Larry Dobbs · Posted: Mon Apr 21, 2008 7:10 pm Post subject: stock piston for 2001

I just bought a couple of top end kits I thought would be for a stock CR250, 2001, but these pistons are domed and mine are flat? Can someone tell me what is stock for what or are they A verses B or something like that? Any help would be appreciated Surprised

John Stafford · Joined: 23 Jul 2001 Posts: 251 Location: Danville, Ca

Larry!!!

Take those pistons back to wherever they're from!

Then call me.

Ian Harrison · Posted: Tue Apr 22, 2008 12:20 am Post subject:

Hi Larry

I love questions like this, right up my street (alley?)

There are 2 possibilities for those pistons (there are more, but then you are going way back before 1986):

1986 - 1996 used a dome top 2-ring piston. Some guys use these on the later barrel induction engines 1997-2001 as they seem to give less detonation (but the head must be squished and volumed to suit).

1997 - 2001 as standard was a flat top 2-ring piston and is probably the most popular in barrel induction race engines. (and is what you were after). The Honda part number for the bare piston is: 13101-KZ3-505 (A size) or 13102-KZ3-505 (B size).

2002-2004 crankcase induction used a flat top 2-ring piston. (This is what we use in our race engines)

2005-2007 crankcase induction uses a dome top single ring piston.

If your piston has a cutout at the rear it is a 1986-1996

If it has no cutout it is a 2005-2007.

A, B, C & D
Pistons (and cylinders) are graded by size.

If you look around your cylinder flange you will see a punched A or B.

This tells you that when the cylinder left the factory it had a finished bore size of:

A - within tolerance of 66.34mm
B - within tolerance of 66.35mm

Pistons are sized the same way. Honda produce A & B, aftermarket also produce C & D as well (Wiseco go even bigger!!).

My interim Super CR250 has a 68.5mm bore

So sizes are:

A - for 66.34mm bore size
B - for 66.35mm bore size
C - for 66.36mm bore size
D - for 66.37mm bore size

If your cylinder has been replated it could be any size, but without instruction most platers would finish to 66.34

As a by the way, Honda in their wisdom have discontinued their Flat Top A piston for the crankcase induction motor. However, we find the B piston runs fine even in a new 'A' barrel, and we don't suffer any seizures. It runs a clearance of just over 2 thou (yes Erik I was brought up on thous!!).

Just to confuse things aftermarket manufacturers also have their own systems of numbering/marking.

Wiseco include the bore size in their part number and the part number is stamped on the top of the piston with a series of dots.

Prox mark the top of their piston (in black ink) with a number and their part numbers all end in A followed by a sizing number as below:

Honda size A = Prox part number ends A = Piston marked 0 = 66.34mm bore size
Honda size B = Prox part number ends A1 = Piston marked 1 = 66.35mm bore size
Size C = Prox part number ends A2 = Piston marked 2 = 66.36mm bore size
Size D = Prox part number ends A3 = Piston marked 3 = 66.37mm bore size

Wonderful Shocked

Having said all that if you post the part No. I'll tell you exactly what it is Cool

Best Regards

Ian Very Happy

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Ian Harrison
Viper Racing UK
www.viper-racinguk.co.uk
sales@viper-racinguk.co.uk
+44 7984 225 564
+44 161 343 2009
Championship winning Superkart race team 1997-2012

Andy Kiker · Posted: Tue Apr 22, 2008 5:57 am Post subject:

Dan Davis · Posted: Tue Apr 22, 2008 7:38 am Post subject:

Here is another source for tall acorn nuts and washers & they are really shiny....these guys really have a bunch of stuff we can use.....they still add up pretty quick tho.

http://www.rtschassis.com/catalog/partsbrowse.php?cat_ID=6&subcat_ID=36#

Larry Dobbs · Posted: Tue Apr 22, 2008 8:27 am Post subject:

Thanks Ian.
What about coated pistons? I don't even know what coatings I am talking about!