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Author Topic: Wrist pin bias.  (Read 4222 times)

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Offline Sam Green Racing

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Wrist pin bias.
« on: August 27, 2005, 04:57:31 PM »
I have been tuning and building Honda motors since the early sixties but mainly the smaller ones up to 175cc.
In these motors the bias for the wrist pin is towards the back of the piston.
Is it the same on all the SOHC4s, as I have never had a four apart ?
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Offline oldbiker

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Re: Wrist pin bias.
« Reply #1 on: August 28, 2005, 01:46:33 AM »
Hi Sam, I've just measured one of my spare pistons for the cb400f and I find the wrist pin (gudgeon pin to us limeys) is .002" offset towards the inlet valve side.
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Offline Tim.

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Re: Wrist pin bias.
« Reply #2 on: August 28, 2005, 10:55:26 AM »
I thought when I was eyeballing my piston the hole seemed to be a bit towards the back  ;)  Learn something new everyday - I would have assumed it to be dead centre.  Why the offset?  Presumably something about the vector of the connecting rod changing through the stroke etc, but I'd be curious to know.
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Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #3 on: August 28, 2005, 02:17:33 PM »
Thanks for the input John, and did you find out what it was we both could'nt remember.


Thanks Tin Tin, your on the right track.
It's not a quiz, it's a problem I have with a set of pistons I just bought.
The arrow points to the front, the wrist pins bias is to the rear but the valve cut aways seem back to front. ??? ??? ???
The pistons in question are Honda CA95, a small early 154cc twin.
The pistons are after market ones from a Japanese company.
Could the manufacturer have messed up and the pistons have eventualy got onto the market ?
The reason I am in this quandery is I have never seen a piston from this model before.

Regards Sam.
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline MRieck

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Re: Wrist pin bias.
« Reply #4 on: August 28, 2005, 03:47:34 PM »
Sam, just about every piston I've seen has about a 1mm bias towards the intake. Yosh pistons had slightly more. For TinTin this helps reduce skirt loads which peak about 70 to 75 degrees ATDC. Long rods also help reduce side thrust as well as increase dwell ATDC which has been a long standing belief to produce more power. That thinking is under debate these days.  Maybe that engine has some kind of wierd rod/stroke ratio though it seems improbable.
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Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #5 on: August 28, 2005, 04:07:48 PM »
Hi mike,

The three motors that I am involved with are C92 CB92 C95.
The 92s are 125cc, the 95 is 154cc and all have 41mm strokes.
Race pistons for the CB92 have no bias at all.
The CA95 pistons should be the same as the C95 ones but with much higher compression.
I don't like the looks of them as the larger valve recess is at the front if you go off the arrow and the fact that the bias is allways to the rear.
I think I will try to get myself a genuine Honda set.
I think there is a firm called Ohio cycles that sell them.
Thanks for your time and input.

Regards Sam.
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RS 175. sprint/land speed bike
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Offline MRieck

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Re: Wrist pin bias.
« Reply #6 on: August 28, 2005, 05:25:58 PM »
Sam, the larger cutouts are on the exhaust side of the stock 750 pistons if that helps.
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Offline MRieck

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Re: Wrist pin bias.
« Reply #7 on: August 28, 2005, 05:30:54 PM »
PS Sam...if they are higher compresion the exhaust relief will naturally be larger. I think they will be OK. How about a picture?
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Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #8 on: August 28, 2005, 05:32:53 PM »
Mike ,  The only 750 pistons I have seen are the Wiseco 836 that we have and the stock ones that are still in the bores of next years motor.
I thought the stock 750 pistons had two indentations for the exhaust valve so they can go into the left or right cylinders.
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CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #9 on: August 28, 2005, 05:40:02 PM »
Mike, can't do pics as am at work but the guy that I got them off is still showing a pic of the on ebay USA under Honda CA95 motor cycle spares.
It's quite a good pic of the fact that they are high comp ones, It's a massive difference from the low comp ones.
He is selling them as a top end overhaul kit with a set of valves and a complete gasket set.
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline MRieck

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Re: Wrist pin bias.
« Reply #10 on: August 28, 2005, 05:48:45 PM »
Quote from: samcr750 on August 28, 2005, 05:32:53 PM
Mike ,  The only 750 pistons I have seen are the Wiseco 836 that we have and the stock ones that are still in the bores of next years motor.
I thought the stock 750 pistons had two indentations for the exhaust valve so they can go into the left or right cylinders.
the larger reliefs on the intake side would be for OS valves IMO. Good exhaust cutouts on Wiseco are natural...to compensate for the L/R orientation as well as increased compression.Sam, I mock it up and run it through by hand and check valve to piston....it takes time but....The Japs do good stuff, it's hard to imagimine that big a Fup
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Offline MRieck

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Re: Wrist pin bias.
« Reply #11 on: August 28, 2005, 05:58:35 PM »
PS Sam, your L/R orientation comment concerning the exhuast valve shows excellent apptitude/knowledge IMO. Mike
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Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #12 on: August 28, 2005, 06:00:56 PM »
Mike, I have the pic up on ebay but dont know how to get it over to you.
Any ideas.
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #13 on: August 28, 2005, 06:05:04 PM »
Mike I think I have Sent it to your email address.

Go check.
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline MRieck

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Re: Wrist pin bias.
« Reply #14 on: August 28, 2005, 06:40:14 PM »
Waiting for it sir.
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Offline MRieck

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Re: Wrist pin bias.
« Reply #15 on: August 28, 2005, 06:46:43 PM »
Sam..post the ebay link.
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Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #16 on: August 28, 2005, 06:50:02 PM »
Mike have just checked and it says I have sent it.
The other guy that is here with me that could show me how to do it is asleap.
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #17 on: August 28, 2005, 06:51:20 PM »
Mike have just checked and it says I have sent it.
The other guy that is here with me that could show me how to do it is asleap.
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #18 on: August 28, 2005, 06:53:37 PM »
Mike don't know what is going on.
I have just replyed twice and it's not gone.
Let me try again.
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #19 on: August 28, 2005, 06:54:53 PM »
Mike how do I post an ebay link?
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline MRieck

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Re: Wrist pin bias.
« Reply #20 on: August 28, 2005, 06:59:26 PM »
Copy and paste. Sam...don't worry about it. It will get here-some time it takes time. Don't worry. Besides....don't you have a job to do!! ;D ;D ;D
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Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #21 on: August 28, 2005, 06:59:41 PM »
Think I have sent to your email address.

Have a look.
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #22 on: August 28, 2005, 07:40:17 PM »
Mike I sent the page then I sent the link but they both came back.
I have had problems posting to your email address before.
When my workmate wakes I will get him to show me how to do it, thats if you hav'nt gone to bed.
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #23 on: August 28, 2005, 08:15:29 PM »
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline Sam Green Racing

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Re: Wrist pin bias.
« Reply #24 on: August 28, 2005, 08:27:42 PM »
Will be on Monday night Mike.
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike
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