Piston Rings GT380

Craig380 · Post by **Craig380** » Mon Dec 15, 2008 7:27 am

Interesting, for the K model onwards, the parts book does NOT specify different numbers for keystone and plain rings ... I wonder if they changed to 2x keystone rings per piston after the J model?

As said above, all I can tell you is I've run 2x genuine Suzi keystone rings per piston on genuine Suzi pistons for 10 years / 10,000 miles with no problems at all, and the bike will do a genuine 95+ mph ... however, that is new rings on good used pistons, so it's also possible the ring grooves have relaxed a little.

I think / think I may have an untouched box of genuine rings at home, I will check and report. Problem is, I'm pretty sure all the ones I had were keystone type .....

I'll check my Clymer too, I don't remember anything in there about different ring types.

Coyote · Post by **Coyote** » Mon Dec 15, 2008 8:42 am

This is very perplexing. It appears as though all rings 73 - 77 were sold in sets - 2 per box. One would assume that each set would contain 1 of each type ring.
Motor City shows 3 different part numbers (+.050) used over the years for the 73 - 77 GT380

The first was 12140-33701
Then to 12140-33711
and currently 12140-33102-050

For what it's worth, the later part number is available from them at $17.10 per set.
The Clymer manual clearly depicts the difference in the rings on page 39.

Triplerocky · Post by **Triplerocky** » Mon Dec 15, 2008 9:59 am

my knowledge, for what is worth (3 complete rebuilts done):

1- GT380J has "Dikes" top ring and "flat" bottom ring (unless an updated piston)

2-GT380K->B has "keystone" top ring and "flat" bottom ring

3-GT380K->B OS 0.5 ring set #12140-33701

4-#12140-33711 is the standard ring set for the italian market only (GT380M onward), where the standard bore was 55 mm. (384 cc.), ence 1.0 mm. larger than the "rest of the world" GT380 54 mm. bore (371 cc.) and corresponding to a OS 1.0 mm.

5-#12140-33700 DO NOT show up anywhere in my 1977 GT380 parts list catalogue, that pen correction is suspicious;

6-someone in the past years confused the rings the box

TLRam1 · Post by **TLRam1** » Mon Dec 15, 2008 10:34 am

Thanks for the feedback.

Looking at the side covers and tank decal (I will have to match up decals closer) but....It looks like the online service manual is a 72 GT380 showing different rings for the top and bottom groove of the piston. I am wondering if after 72 they changed to the same ring on both top and bottom and neither are keystone.

Three rings work and three do not. The rings do not go in the top or bottom groove whether on the new pistons or my old pistons, (only checked the top on the old piston) and I checked more than one piston.

I will work more on this later tonight or this week sometime.

Barry S. · Post by **Barry S.** » Mon Dec 15, 2008 11:44 am

http://www.ozebook.com/compendium/techb ... in2-73.pdf

A while back H2RICK posted the differences in I believe it was gt250/380 pistons, I think I have it saved at home, I'll check when I get there.

GT Tim · Post by **GT Tim** » Mon Dec 15, 2008 11:46 am

TLRam1 wrote:What I have found....not much.

1. The pistons seem to have square grooves.

2. I don't have an accurate enough mic for a good measurement.

3. The 3 rings will not work in the top or bottom groove, markings are facing up.

4. Tried the 3 rings in my old pistons, same result.

5. My old pistons seem to have square grooves also.

This is a 75 GT380, could they be different than other models? I am not sure where to go from here.

Nope Tim, this is something you wouldn't know, no problem, I am not sure what direction to go yet.

I will look up part numbers on the boxes and see what they go to.

These are .50 OS

Piston - 12110-33701

Rings - 12140-33700 the last 0 was changed to 1, probably the same but a number update.

I just got off the phone with my dealer. He searched the problem for me and told me that the -33700 and -33701 piston rings are correct for the piston number 12110-33701.
He also said that ther is a top and bottom ring as far as thickness ; and they are a one way fit. The letter should face upwards.

Problems may lie according to them:

-You need to determine which is the top and which is the bottom ring

-You need to be sure you have them facing upwards

-The piston for that number should be a keystone piston--you may have an incorrect piston, may not be 12110-33701 in actuality. Strange that they fit on one piston and not another...makes me wonder.

-Make sure the rings I sold you are correct and keystoned...they should be...both of them.

If they are not both keystoned , send them back and I will refund your money. If they are both keystoned, your problem lies elsewhere.

Craig380 · Post by **Craig380** » Mon Dec 15, 2008 11:53 am

the service bulletin posted by Barry S says both top and bottom rings for the 380K should be keystone. Wow. This is a strange one ....

Barry S. · Post by **Barry S.** » Mon Dec 15, 2008 12:29 pm

http://www.ozebook.com/compendium/suzi/ ... istons.pdf

TLRam1 · Post by **TLRam1** » Mon Dec 15, 2008 10:37 pm

Yes they are .50 over as indicated on the top right side by the ring opening and RN on the left side. Check your rings Craig and see what you can tell.

I take it from what people have posted, Keystone Pistons have an angled groove to match the keystone ring, correct?

My Clymer does mention ring photos as Chris pointed out on page 39 but does not denote differences between models.

I will play with my old pistons more and test in both grooves.

Contradicting info

from what Chris found, rings are different…….. to

Barry’s - H2Rick saying both are the same…. to

The Part number Tim checked on is J model only…… to

Tim’s part guy which correlates with what Chris found…… to

Craig’s 2 rebuilds and never matched up rings with grooves

I am not contradicting what anyone is saying or has found out.

But the facts before me are.

If my new pistons are incorrect than the old ones would be the same as I have the same issue with them and the rings. I would not think this would be the case but possible for sure.

To

Craig's twice rebuild and never matched rings to grooves I think it unlikely you would luckily get the square ring in all the bottom grooves and keystone in the top groove without looking.

TLRam1 · Post by **TLRam1** » Mon Dec 15, 2008 10:42 pm

Tested again

I tried again the new ring in my old pistons, top and bottom, doesn’t fit.

The new rings that work will fit any groove on the old or new piston. The rings that do not work will not go in any groove on old or new piston.

I did notice something between the rings. The old rings look chrome and the new rings are a dark steel with a lighter band on the outside. I took a photo but the shiny chrome does not show well. If the light hits it properly you will have a nice reflection on the old ones.

Incase you think my eyes got the better of me and I made up this number. Lol

GT Tim · Post by **GT Tim** » Tue Dec 16, 2008 1:20 am

Dealer tells me any last digit number change is an update. Will work in ANY Model afterwards (-00000 to -00001) and back.

A 4th digit change is a fudamental change or difference in part, be it size, or construction. (-00000 to -00010)

What you are trying to show is moot according to them, just an update. Not an issue

That's why -00000 doesn't show anymore. My software is an older version and does.

SEND THEM BACK. It is worth it to make this go away. I'll give you your $45.00 + $3.50 I owe you.

Coyote · Post by **Coyote** » Tue Dec 16, 2008 9:31 am

From what all you found Terry, it is becoming obvious that at least SOME rings are incorrect. Were the boxes sealed? If not, they could have got scrambled eons ago by some ham fisted parts guy. I can see it now. Rings laid out for comparison and slipped back in the wrong boxes.
That being the case would not make the error Tim's fault.
At least new rings are available. You can get them from Motor City or through your dealer. Just be sure to be armed with the current part number. 12140-33102-050.
If all your old rings will slip in the grooves of your new pistons, that would pretty much eliminate the pistons as the culprit.

TLRam1 · Post by **TLRam1** » Tue Dec 16, 2008 9:32 am

Tim this is no reflection on you, I am just trying to get this sorted out. At this point I don't know which is correct, piston or rings, or which is not.

Do you still have your 380 pistons you can take a close look at the grooves to see if they are tapered and any other rings you can try on them?

Suzukidave · Post by **Suzukidave** » Tue Dec 16, 2008 9:40 am

some keystone ring info http://www.3cyl.com/~mraxl/gt/manuals/gt750man/sr29.htm

TLRam1 · Post by **TLRam1** » Tue Dec 16, 2008 3:53 pm

Coyote wrote:From what all you found Terry, it is becoming obvious that at least SOME rings are incorrect. Were the boxes sealed? If not, they could have got scrambled eons ago by some ham fisted parts guy. I can see it now. Rings laid out for comparison and slipped back in the wrong boxes.
That being the case would not make the error Tim's fault.
At least new rings are available. You can get them from Motor City or through your dealer. Just be sure to be armed with the current part number. 12140-33102-050.
If all your old rings will slip in the grooves of your new pistons, that would pretty much eliminate the pistons as the culprit.

I will check the new rings on my old piston again tonight for fitment. I have checked many various ways I can't keep it straight.

Who knows I may have wrong pistons and rings, I need to secure another set to help sort this out or start over.

These are one of those times you being the seller you wish it all worked out and would drive me nuts if I were but no it's nothing to do with Tim and hope he understands that. I appreciate his efforts (and everyone else's) in the investigation dept. to help me resolve this.

I want to be thorough as not to prematurely go in circles.