Good news
So I finished the top end tear down this morning.
Good news is that all I need is a new set of pistons and a rebore. Basically the current pistons are way too loose.
When I got the bike 2 years ago it had oversize 0.05 pistons in but they had seizure marks and were generally shot. I put in fresh .05 pistons from Cruzinimage after honing the cylinders.
It seems that the cylinders were pretty worn out and the honing compounded the problem by enlarging them even more.
I just measured the piston clearance in the center cylinder (the worst one) and I can fit a 0.15mm feeler gauge. That’s a lot of gap! The factory recommended gap is 0.045mm.
On the bright side I measure the lateral play on the con rods and they are all under 3mm which is within specs and there is no vertical play so I don’t need to rebuild the crank.
It is getting difficult to source pistons. Suzuki is out of the oversize 1.00. I did finally find on ebay malaysia a set of NOS oversize aftermarket pistons made by Right Way, a reputable OEM manufacturer. They are on their way along with suzuki pins, clips and small end roller bearing.
The only downside and they are 1.50 oversize which is close to the maximum bore possible, I believe 1.75 is max. I guess I have only one rebore left after that.
Top Down
I quickly took the head off tonight as I am curious to see what that new noise is. I think I found out.
The cylinders are worn out with a strange marbled pattern and the pistons, especially the centre one, have a lot of play. Just touching the piston’s head, I can wiggle it around and make it click in the cylinder. It seems like my reproduction pistons fitted to rehoned, but not rebored, cylinders was not quite right. I wish I had checked the clearance then…
Hopefully when I dig in deeper this weekend I wont find any disaster and all I need is a rebore and new pistons, OEM this time.
Funny noise
Since I sold my harley a few weeks ago, I have been riding Suzie a lot more. Between my work commute and the odd weekend ride, I put 500 miles on her last week alone. I even went for my first long ride, 4 h with my son.
I recently noticed a strange clicking , rattling noise from the engine. It’s hard to describe but it sounds mechanical, clock like, and is linked to engine speed, not the bike speed. It’s more noticeable on low loads and it has become increasingly more present.
My first suspicion was the nylon timing gear that drives the point cam. This gear is notorious for shattering after extended use and I thought it might be going bad. Well I was both right and wrong.
The gear was indeed cracked and would have blown in my face pretty soon. However, after replacing it along with bearing seal and other doodads, the noise is still here and getting a lot more obvious. It has gained more of a deep rumble quality with a ticking layer on top. It used to sound like an oversized clockwork now it’s getting to sound like a washer and dryer.
I now suspect that more serious things (read expensive) are happening in there. I will open the cylinders this weekend to check in the small end bearings and piston clearance is ok. if that’s fine then it must be the crank bearings which means a complete tear down and splitting the case.
Our work is never over…
Tire swap
I had the wrong tire fitted to the front wheel and I finally got around to change it. The current tire was too wide and the tread design just didn’t look right for a 70’s bike. I manage to source a duro tire in the correct, and now rare, size of 3.00-19 with a perfectly vintage design.
I also changed the fork oil as it was getting quite bouncy. The bike feels quite a lot nimbler in corners.
Yan's GT380 
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