GT380 Piston Rings

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grumpy56
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Suzuki 2-Strokes: 1970 T350 Restored; 1972 GT380 Build
Location: Yorba Linda, CA

GT380 Piston Rings

Post by grumpy56 »

Hello All. The 1972 GT380 I'm rebuilding had one keystone and one standard ring on the right and left pistions. Do the ring sets being peddled include both types of rings? There was a new center piston in this engine and I noted that both rings were "standards". Thank you.
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jabcb
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Suzuki 2-Strokes: 69 T350 thru 75 GT750
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Re: GT380 Piston Rings

Post by jabcb »

For stock pistons there should be one keystone & one standard ring. See the service manual for details:
https://www.oldjapanesebikes.com/mraxl_ ... /index.php

This would vary for aftermarket pistons. The Wiseco pistons I recently installed have two identical rings.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
grumpy56
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Posts: 218
Joined: Thu Nov 20, 2014 11:08 pm
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Suzuki 2-Strokes: 1970 T350 Restored; 1972 GT380 Build
Location: Yorba Linda, CA

Re: GT380 Piston Rings

Post by grumpy56 »

Appreciate the info jabcb. Do you know the P/N for the set of rings for the stock Suzuki piston (one keystone and one standard)? My parts catalog identifies ring sets as 12140-33010 for the standard and 12140-33011 for the keystone. A previous holder of the manual penciled in Bulletin #74-8 dated 2-20-74. I have been unable to locate that service bulletin.
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jabcb
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Re: GT380 Piston Rings

Post by jabcb »

Search for the word, “piston”, in this list of service bulletins: https://ozebook.com/compendium/techbuls/index.htm
Part #s are here: https://www.partzilla.com/catalog/suzuk ... crankshaft

Did you check clearances to see if you should use the next oversize pistons?
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
grumpy56
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Posts: 218
Joined: Thu Nov 20, 2014 11:08 pm
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Suzuki 2-Strokes: 1970 T350 Restored; 1972 GT380 Build
Location: Yorba Linda, CA

Re: GT380 Piston Rings

Post by grumpy56 »

Yeah, I looked through that bulletin list but did not see the one I referenced. Honed the cylinders and I am still at 54mm so will stick with standard size pistons. Hope to find Suzuki if I can. Would you recommend the Wisecos? Do they use two standard rings on each piston?
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tz375
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Re: GT380 Piston Rings

Post by tz375 »

There appear to be a few pistons and rings on ebay with new piston kits available from Cruisinimage and a UK based company.

Might be a good time to go up one size and have fresh bores, pistons and rings.
grumpy56
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Suzuki 2-Strokes: 1970 T350 Restored; 1972 GT380 Build
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Re: GT380 Piston Rings

Post by grumpy56 »

Saw those on e bay, but have heard mixed reviews about Crusin Image and some of the other "off brands". My understanding is all (or most) of them come from China, so am hesitant. Those Crusin Image kits sure are cheap though compared to OEM or Wiseco.
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jabcb
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Re: GT380 Piston Rings

Post by jabcb »

The Wisecos are good but pricey. The pistons I’ve purchased included rings, pin, bearing & circlips. Their rings are different that Suzuki’s.

No experience with Cruisinimage. Some members are satisfied with them.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
grumpy56
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Posts: 218
Joined: Thu Nov 20, 2014 11:08 pm
Country: USA
Suzuki 2-Strokes: 1970 T350 Restored; 1972 GT380 Build
Location: Yorba Linda, CA

Re: GT380 Piston Rings

Post by grumpy56 »

Did you get the Wiseco kits on e bay? I tried their website, but they don't seem to have them for the 380.
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jabcb
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Re: GT380 Piston Rings

Post by jabcb »

I got the Wiseco pistons for the GT550 from Paul Miller. He is eBay seller jrwdfa. See: http://www.ebaystores.com/paulmillermotorcycle

Paul lists only some of his parts on eBay. He might have a complete set of Suzuki or Wiseco pistons.
He has a small business & doesn’t spend a lot of time in the office. Seems to travel a good bit to acquire old inventories of NOS parts.
Can be hard to reach. Phone: 860 828-1771 Might also try contacting him via eBay.
I’ve called him a few times to get parts that were otherwise pretty much unobtainable & he had what I needed.

The Wiseco pistons for the T500 cafe build are “crazy-looking” modern pistons that were recently manufactured. Seemed like lots of sellers had them.
They are similar to these Yamaha pistons: https://www.youtube.com/watch?v=2G8FVtMzGAk&t=37s

GT380s & GT250s were popular. With some effort you should be able to find what you need. The search for parts is just part of the fun of working on vintage vehicles.

Wiseco doesn’t list pistons for vintage bikes. But I’ve heard of a few times when they made a batch of pistons for someone.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
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tz375
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Re: GT380 Piston Rings

Post by tz375 »

I have Wiseco pistons in my GT750 and used them on a prior build without issues. I melted a pair years ago in a Yamaha RD. I used CruisinImage pistons in a drag race GT750 with zero issues and use them in all street GT750 builds. They are good pistons. Well made and incredibly cheap.

For the street I would use cast pistons every time and forged in a very high performance motor that I know will be properly warmed up before use.

YMMV
grumpy56
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Suzuki 2-Strokes: 1970 T350 Restored; 1972 GT380 Build
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Re: GT380 Piston Rings

Post by grumpy56 »

Thank you both. Will continue the search!!!
Vintageman
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Re: GT380 Piston Rings

Post by Vintageman »

I use partzilla.com and OldJapaneseBikes.com to help sort our OEM dimensions and part numbers. Sometimes Partzilla will show an older interim number ("Replaces xxxx-xxxx") and that helps you then search for it on eBay if can't find the others. Sometimes ring part #s have been changed more than once. The other site has EOM parts manual so you can see how they started for part # and search that too. Check Service bulletins there also. I have not seen GT380 ring quality issues, so reason ring part numbers change may not be due to quality issue. Yes sometime they change ring style early model vs later ones. OEM parts manual, if new enough, can show the difference per model years. For example The early T350 is different then later years. I have bought the wrong ones only to learn and try again

CruzinImage 's Piston themselves IMO are just fine. Sometimes a mistake in subtle dimensions here and there, possibly when they reversed engineered the OEM part but, you need to check and decide for yourself if true and then if a problem. Piston pin sometimes heavier than stock and may fit little looser. Too wide gap between rod side to side play. If you don't like what you find, wait for OEM to show up as I have at times: But can take a while! I try to buy spares now

There is/was a post (can't find it now maybe "cancelled" :shock:) about aftermarket piston and ring including longevity data. The person did not say names but, in one pic there was the classic white plain box I have seen these piston come in. not sure. To the point of post was most pistons were just fine but, the ring are not quite as good as OEM and therefore did not last as long if that is an important criteria.

What I have seen so far is you can replace Cruzinimage's rings with OEM . I have checked a couple sets now and worked out well. Just did T350 1.0mm and with OEM rings fit per OEM spec. The two ring sets do look different. I am not a metallurgist. OS piston are getting rare for some bikes and he has them . I have used his pistons but so far with OEM wristpin, OEM Rings and OEM little End Bearing. So far all is well and no complaints. Maybe I don't need to uses these OEM parts instead of his, but no problem if I do.

He banded me on eBay for pointing out a dimension issue with GT750 piston years ago. I just contacted him about a dimension issue I saw in hope he would correct down the road when they produce next batch, I did not rate him. It is amazing what he has done and hope he continues and takes feedback to improve only if needed. I now order from his web site directly when I want to. A few orders ago the package was retuned to Japan from USA once received at port, not clear why but, something with paper worked? Contacted him and he shipped again but, same thing happened exactly. Contact him to see what issue was but would not respond this time. I was out my money spent as well.

I just ordered Pistons and then Conrods. Both came in fast.

He is not expensive compared to other options if you have other options.
Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400 (Daytona Cyls),
grumpy56
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Posts: 218
Joined: Thu Nov 20, 2014 11:08 pm
Country: USA
Suzuki 2-Strokes: 1970 T350 Restored; 1972 GT380 Build
Location: Yorba Linda, CA

Re: GT380 Piston Rings

Post by grumpy56 »

Thank you Vintageman. Appreciate the helpful data.
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