Scooterotica

Just set about building the top end of my GT186 only to find that the people who built my crank have fitted the 115mm RD400 conrod (*) when I asked for a 110 conrod.

Even with a 3mm packer the piston protrudes right out of the barrel to such an extent that the top piston ring pops out!

Now I've calmed down, I can see that the conrod doesn't catch on the casing. So, I'm thinking I may be able to use this crank

Thoughts please

(*) actually, I think this is the case but I need to check it for certain on Monday. When I picked it up he certainly said it was RD400 and I can't find any reference to the RD400 having any length conrod other than 115mm.

hi,i think the rd250/350 is 110mm long,and the rd 400 is 115mm and more suitable for a jap conversion piston i.e.kx 250 or ts 250 as these have a smaller compression height than a lambretta piston,only thing is these have a 18mm gudgeon pin,so you would have to use 1mm thick bushes,perhaps mb do a race tour piston that might work with that rod,cheers.

just re read your post,doesnt the gt 186 use a mitaka rd350 lc piston,so dont really know your options with that kit,but might be able to use it with a lambretta barrell.

It should work with an 8mm pack plate and some long studs but jacking the barrel that much might give you some exhaust alignment problems.

dt 125 ypvs was the one you wanted

I asked for a KE175 conrod as that's what I've got on my TS1 and it goes in without any machining, and with thrust washers. But, it was one of those "leave it with me, you want the better Yam conrod. I'll sort it for you" moments. Except, the builder seems to have missed the basic point that I wanted a 110 not a 115. I even wrote this down too!

Thanks for the replies. The clubman that is going on this engine needs a bit of welding anyway (it's going to be used for time trialing and going over rocks and boulders) so I think I'll proceed on the 8mm route at the moment as I really need to get this engine built quickly, rather than strip out the crank again.

As regards the barrel studs, are P2 studs longer than Lammy ones. It's the original GP125 ones that are in there at the moment?

The MB long studs should do you, I've got a 3mm packer and there is loads of stud sticking through the head....so nuch in fact that you can;t get the barrel off without droppiung the engine

P200 studs are longer

just had 6.5mm and 8mm packers made if thats of use

Just wondering if the use of a packer would increase the primary compression and if it did, would it be significant and be a good or bad thing?