T500 piston types

[casperdog]

Hi, just stripped the top end off my T500 to find that when its been rebored 1mm over, two slightly different types of piston have been fitted.
The bike was a non-runner when i bought it recently. The bores look in good nick.
Dimensionally they are the same, but the forging on the inside at the top is different. One has the ridges one doesn't.
They weigh the same, within 6 grams.
Any body shed any light on what i've got.
Thanks
Phil

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[Zunspec4]

Hello Phil,

What you have there is 1 T500 piston (un-ribbed) and one GT750 piston (ribbed). These pistons are interchangeable although it is unusual to see both types fitted together in a T500. The ribs on the GT750 are to make them stronger and I used to use them in a T500 race engine. Why the 2 types were fitted is open to speculation as you would normally install them in pairs if you re-bore the barrels.

Cheers Geoff

[casperdog]

Thanks Geoff, that's great info for a novice to these bikes like me. The rings were stuck but i've managed to free them after a struggle.
My plan is to replace the rings and a give the bores a quick scratch with the hone and see what happens.
I've been doing loads of browsing on ebay for some rings (1.5mm thick type) and i think these are the ones i need.
https://www.ebay.co.uk/itm/NOS-OEM-SUZU ... 2749.l2649" onclick="window.open(this.href);return false;
They are on the way now so we'll see.
Cheers
Phil.

[Zunspec4]

Hi Phil,

Early T500 rings were of different thickness to later ones, sorry I can't remember when this happened. AFAIK later T500, and also the GT750, pistons used the same rings. I'm sure other more knowledgeable folk can provide details.

Cheers Geoff

[karl pa]

I am not sure any 500 rings will fit 750 pistons. 750 rings 12140-31720 , GT500 rings 12140-15711, T500 rings 12140-15710.
A few years ago I was going to replace the rings in my GT500, Suzuki showed the GT750 rings as the replacements, but the GT500 rings were much thicker.

[Zunspec4]

Hi karl,

I am also unsure of the details concerning the interchangeability of 500 and 750 rings. When I bought 750 pistons they came complete (piston, pin, circlips & rings) and they certainly fit the T500 engine. I haven't got any loose 500/750 rings to measure unfortunately.

Cheers Geoff

[karl pa]

It can get confusing when part numbers supersede to new numbers, and they supplement parts for others. It is easier when replacing all the parts,compared to matching parts.
I installed early 750 pistons and rings in my 75 T500, so I know they interchange that way. But the newer 750 uses thrust washers between piston and rod, and 500 doesn't (I thought they did also but the parts book doesn't show them,guess that's why I could use early 750 pistons) so I am not sure they can interchange the other way.
I think the 500 came with oil grooves on the pistons and rings on standard, but I seen 500 pistons without these oil grooves, (or where they 750) If you do a search of 12110-15103, GT500 rh std piston, you find some with oil grooves and some without,but same part number
The 750, GT500, T500, all have different part numbers for pistons, the T500 has different numbers for early and late. And the 750 also.
So it can get very confusing matching rings with pistons, especially when uncertain what pistons.
My used set of T500 rings measure 1.97 mm thick, can't find my 750 rings now.

[casperdog]

I agree Karl, very confusing with different part numbers for supposedly the same part, superceeded part numbers, different parts with the same part number.....
The rings i have measure 1.5mm thick and have a tapered top edge - they measure about 1.3mm on the inner edge.
They are both the same on the two types of piston i have fitted on the bike.
I did manage to get the stuck rings out undamaged so i might put them back in anyway.
Cheers
Phil.

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[karl pa]

You can check ring gap to see if they have to much wear, some of my bikes have excess ring gap but still run fine, all depends on riding style, mine is fairly gentle.

[Zunspec4]

Good morning,

I believe the pistons with the oil grooves around them are of the earlier type. The set I fitted to my T500M also had the window in the piston, so definitely early in that case (I must change those out). When using GT750 pistons I never used thrust washers either side of the little end, assuming that the t/washers on the big end kept the rod central. I think that if you have a piston, with rings/pin/circlip etc., They will fit and work from any model year, including GT750.

Cheers Geoff

[karl pa]

I agree any 750 piston will fit a 500. But a 500 piston will not fit a 750 with new style crank that uses washers at small end, without machining wider.
Both of my GT500 engines have oil grooves on pistons, so I think all 500 came with them, but replacement ones did not.