Polini 70cc cylinder kit for a 1978 Yamaha Chappy LB50. Studs are too long???

John Lusignan /

I bought a Polini 70cc cylinder kit for a 1978 Yamaha Chappy LB50. I also bought the Puch hi compression head. I just installed them. Everything fits great. My only problem is that it seems that I might need a spacer/standoff for the cylinder studs. I have the nuts threaded all the way down and there is still approximately 15mm of bare unthreaded stud left. I've attached a photo so you can see what I mean.

My initial thoughts are +/- 15mm of washers or some kind of standoff/spacer to occupy that space so i can torque down the head properly.

My question is, have any of you seen this before and do you have any resolution?

Thanks so much

20190110_194054[1].jpg

Re: Polini 70cc cylinder kit for a 1978 Yamaha Chappy LB50. Studs are too long???

Yup use spacers.

Shaft collars work great

Be wary of spacers that are too thin. They'll gouge the head and loosen up the stud causing an air leak

Re: Polini 70cc cylinder kit for a 1978 Yamaha Chappy LB50. Studs are too long???

John Lusignan /

1. So you've seen this before?

2. What are shaft collars and where would I look for them? I googled them. I see ones with set screws. Is that the type you are referring to? Or is there something else?

Thanks in advance!

Re: Polini 70cc cylinder kit for a 1978 Yamaha Chappy LB50. Studs are too long???

I would go to the hardware store and buy a length of 1/2in. dia. aluminum or steel rod. Cut to length and drill a 7mm hole.

ScreenShot126.jpg

Re: Polini 70cc cylinder kit for a 1978 Yamaha Chappy LB50. Studs are too long???

I suppose you might consider a stack of flat washers or bigger nuts on each of the studs .

Or , source some new correct length studs .

Or , drill and tap for more common 8mm replacements .

Or , drill and tap for all thread and cut to length .

There's always more than one way around a bush . ;)

Re: Polini 70cc cylinder kit for a 1978 Yamaha Chappy LB50. Studs are too long???

Dirty30 Dillon /

The Puch head is thinner than the chappy around the stud holes, hence your issue.

Re: Polini 70cc cylinder kit for a 1978 Yamaha Chappy LB50. Studs are too long???

Baron Von Hamilton /

Puch studs should be closer to the right length. Or get those spacers.

Re: Polini 70cc cylinder kit for a 1978 Yamaha Chappy LB50. Studs are too long???

Barry (Bob) Brown /

Treats sell some that will probably fit - I ran into similar issue with a kit/head.

Puch/Malossi Stud

Re: Polini 70cc cylinder kit for a 1978 Yamaha Chappy LB50. Studs are too long???

John Lusignan /

Thanks Bob!

The original studs are M6 x 116mm and that link you sent me was M7 x 106mm. I assume the holes in the case will M6 and both end of the malossi studs you sent would be M7.

Here's a link to a Polini set that comes with "coupler nuts"

They are M6 x 106. I still think that's 5mm to long but I'll have to double check. But those coupler nuts look like they could be threaded further down the shaft than the original acorn nuts which bottom out at some point.

Any thoughts?

Thanks in advance!

Re: Polini 70cc cylinder kit for a 1978 Yamaha Chappy LB50. Studs are too long???

Barry (Bob) Brown /

Sorry I had wrongly assumed most head bolts would be M7, mine were, but it looks like you found some that will work better than you have.

« Go to Topic — end of thread

Want to reply to this thread?

We'd love to have you join the discussion, but first you'll need to login (or create an account).