PISTON & REBORE advice

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baldock
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PISTON & REBORE advice

Beitrag von baldock »

Does anyone know the upper and lower limits of diameter for each of the 4 stock size pistons?

Is there a marking somewhere on the piston to show what size it is?
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Kristian
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Re: PISTON & REBORE advice

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According repair handbook "Bucheli" Chapter 2.1 the diameter of the standart piston should be:
88,97 - 88,99 mm (10 mm below top of piston).
The limit is: 88,88 mm.

The oversized piston have stamped on top: 0,25 or 0,50 or 0,75 or 1,00 and "IN" for intake side.
The serial piston has just the "IN".

If you need more data search for the repair manual from our italian friends: "WHB_Honda_XR_Kapitel07 Kolben Zylinder.pdf"
Bub, bub, bub...
baldock
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Re: PISTON & REBORE advice

Beitrag von baldock »

thank you Kristian.

Do you have a link for the repair manual as nothing comes up for me on google?
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hiha
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Re: PISTON & REBORE advice

Beitrag von hiha »

10mm below top of piston? That is NEVER the right point to measure the diameter of a piston. Another mistake in Bucheli?
Cheers,
Hans
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Re: PISTON & REBORE advice

Beitrag von baldock »

I'm new to this, where would you measure it, the pin?
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hiha
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Re: PISTON & REBORE advice

Beitrag von hiha »

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Gunnar_HH
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Re: PISTON & REBORE advice

Beitrag von Gunnar_HH »

Hello Baldock,
Here are the measurements for the piston and the piston pin. Most right, the Service Limit.
Also where to measure it.
The next sizes are +0.25 / +0.50 / +0.75

Best regards
Gunnar
Kolbenmass-verschleiss-eng.jpg
Kolben-vermessen.jpg
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baldock
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Re: PISTON & REBORE advice

Beitrag von baldock »

the piston only has 'IN' so I assume is standard size.

Piston measures:
88.62mm (TOP), 89.01mm (MIDDLE), 88.99mm (BOTTOM)

cylinder bore measures:
89.29mm (TOP), 89.30mm (MIDDLE), 89.32mm (BOTTOM)
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Re: PISTON & REBORE advice

Beitrag von baldock »

would the above measurements be ok to just hone the cylinder and put my NOS standard piston/rings in?
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hiha
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Re: PISTON & REBORE advice

Beitrag von hiha »

baldock hat geschrieben: 23. Juni 2021, 00:16
Piston measures:
88.62mm (TOP), 89.01mm (MIDDLE), 88.99mm (BOTTOM)

cylinder bore measures:
89.29mm (TOP), 89.30mm (MIDDLE), 89.32mm (BOTTOM)

would the above measurements be ok to just hone the cylinder and put my NOS standard piston/rings in?
So if I calculate right: the piston has ~0.31mm clearance in the bore, but should have a max. of about 0.10mm. (see the line next to last "piston to bore-clearance")
As you see: Honing wouldn's solve the Problem.. :lol:
You will need a new piston two sizes over. But I would recommend to visit a qualified motor-repair-shop and ask there for measuring cylinder and piston.
Cheers,
Hans
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Gunnar_HH
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Re: PISTON & REBORE advice

Beitrag von Gunnar_HH »

baldock hat geschrieben: 23. Juni 2021, 00:16 the piston only has 'IN' so I assume is standard size.

Piston measures:
88.62mm (TOP), 89.01mm (MIDDLE), 88.99mm (BOTTOM)

cylinder bore measures:
89.29mm (TOP), 89.30mm (MIDDLE), 89.32mm (BOTTOM)
Fascinating!
To me it looks like your cylinder was honed for the first oversize and the original piston was installed. A mistake in the reassembly?
You should hear that much play, it's called piston tilt.
I agree with Hans, ask a good engine repair shop what to do.

Cheers
Gunnar
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Re: PISTON & REBORE advice

Beitrag von baldock »

thanks :top:
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Re: PISTON & REBORE advice

Beitrag von baldock »

I took the cylinder and old standard piston, a new +.25 piston and a new +.5 piston to the machine shop.

The +.25 just dropped straight through the bore with too much slop.

Engineer felt a slight groove in bore then said they'll rebore/hone for the .5 and see if the groove is gone.

If not, I can't rebore to .75 as I don't have a piston that size.

fingers crossed
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Gunnar_HH
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Re: PISTON & REBORE advice

Beitrag von Gunnar_HH »

"a slight groove in bore" That's new for us.
Where does it come from? Do you have a picture?

To take the next size (+0,50) is okay.

Good luck for rebore/hone

Cheers
Gunnar
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Re: PISTON & REBORE advice

Beitrag von baldock »

is there a place you guys get your pistons/rings from in case I need to get a +.75?
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