SR185 Piston

[dapper]

Downtube parted with the rest of the exhaust on Saturday causing scoring to piston and cylinder. Tried to wet n dry them back to a good state, but when rebuilt now have terrible piston slap and can't get her running correctly. So where can I get a new oversize 185 piston and rings from and the cylinder rebored? The cylinder and piston were tuned by Dave Betts (RIP) and he put a dogleg boost port in the cylinder and a hole just under the rings that lines up with it. Based south coast.

[storkfoot]

I'm in work at the moment and my works PC won't give me access to your pics. With having a modified piston and cylinder, I wouldn't just buy any 64mm piston and hope it works. I doubt it will work successfully with the boost port. You might want to consider taking it to either CamLam or MB as they both stock 64mm pistons as oversizes but, at the end of the day, any competent tuner would be able to help.

I have some experience of the SR barrel. I initially started with an SR175 and an Asso piston. This was OK but no more. I seized it a couple years ago when the exhaust nuts came loose.

I then got a 64mm Deanspeed piston from the States which, after MB had given it a rebore and a bit of road tuning, was a pleasure to ride. The Deanspeed piston was a bit rough and ready looking though.

I must have done about 4 or 5 thousand miles but the performance was getting worse and worse over a couple of months. Eventually discovered it needed a rebore, in fact it was so worn it needed to go out to 65! Don't know whether this was the rings too hard or the SR steel liner being too soft. Gut feel tells me it's the steel liner.

It's rebuilt now with a Race Tour 65mm piston although it hasn't gone back in the frame yet. Hope this gives you some ideas.

[Supereibar]

Try a Suzuki piston overbore. Our racer has run faultless from start, thrashing it on the race track two times for six hours. Done 600-800km of pure thrashing.

J.

[soullad]

The SR pistons when new suffered with piston slap due to incorrect machining tolerances, so its hardly surprising that after removing more ali that yours slaps so badly.
Its only been of late that 64mm alternatives have been available, and until then the only reliable source of 64mm standard lammy crown height pistons were the specially made Deanspeed ones from the States. As noted although a touch rough n ready these have proved 100% reliable in the scooters i have fitted them too.
Now thou, with more kits, you have more choice and top of the tree has to be the MB version.
The Suzuki version will require either a rod change or barrel machining so bear that in mind.
As for the sr liner being made of cheese metal - i sincerely hope not......

[storkfoot]

As for the sr liner being made of cheese metal - i sincerely hope not......

Think I'll have to ride a bit more sedately when I get it back on the road, as I'll be running out of oversizes soon

Agree, if you compare the finish of the Race Tour, to the Deanspeed piston, there's no comparison. The other problem with the Deanspeed, of course, is that no-one in UK supplies new rings for them and they have 2 different size rings so neither Mugello nor SR rings were any use. I got a set from the States eventually (before I realised I needed a rebore )

[RinB]

Try Epay

http://cgi.ebay.co.uk/LAMBRETTA-GP-LI-S ... 7C294%3A50

They may do the job ???
or Sundarscoots they have 185 pistons in

[chris2470]

I believe these pistons are perfectly fine but the rings are crap so get some Mugello rings from CamLam and gap them to suit, 0.1mm per Inch of bore.