I need some help here please. I have a 247 Cota around 74 75 vintage on standard bore (72.58) that has bad rattles in the top end. New rings, pin, bearing have not done much to stop the problem.

I bought a new piston and rings advertised for a Cota 250 (72.75) (made in Italy) but have found that under the original packaging they are marked for a Bulty 250 Sherpa. That was crossed out and Cota written in texta. Both pistons are nearly identical. Original Cota has a port on the intake side with oval ends, the new one has a port with rectangular ends. High and low skirts appear to be the same. Ring pegs on the old one are at the front, the new one has them at the rear but as the light is fading here I can't tell whether the ends are adjacent to other ports in the cylinder. One other thing, The old piston has a V shape under under each of the pin holes. The new one has square ones but not as big.

What do you reckon? have the cylinder bored out and see what happens? I would like your opinions on this as this is the last 247 cylinder I have left!! Thanks for any advise you can give me.

Hi cota 247 pistons don't have a window or port in them ,that sounds like a bultaco piston as well,,,

i havn't used a piston with a window in one would this make the engine noisey ?

out of choice I would use the correct piston,,,,,

cota 247 start at 71MM 237.5 CC this I believe was to get round import taxes

,so you could already be on your 3rd rebore 2 more to go

pistons are available from http://kevinbreedonracing.co.uk/products_pistons.asp

also in spain from http://www.rectificados-bellavista.com/Pistones.html

hope this helps cheers helm

Hello Helm

I can assure you the two 247 Cotas I have, have pistons with ports on the intake side. Standard Bore started at 72.58 for bikes imported to Australia but I recall someone saying that those bikes imported into France were slightly smaller in capacity to comply with regulations. Thanks for the reply.

Hi,

my 247 runs on a bultaco piston without any probs and i did the re-bore. Go get it bored out and also check the small end and big end for any play

Dave

Well you probably have bigger problems than the piston.... or maybe smaller. Check the timing! maybe you are a little off or have been using fuel that is too low octane. Second: did you chk crank end play and rod play also? They will cause a lot of noise in there that you might think is piston problems. Also, if you have not done crank seals do those too. Seal leaks cause all kinds of detonation/starving problems that make evil sounds. these are items that you need to chk on all old 2 strokes. get these right and it will be very quiet.

Thanks for that. I should have mentioned at the start that I split the cases and replaced all seals and bearings in the motor about two weeks ago. I also replaced the little end and bearing and at the same time new rings. The rattle was not as great as before but it is still there and annoying me. The clearance between the piston and cylinder is past its use by date. In some areas around 6 to 7 thou and it is no wonder the rattles are there. I will persevere with this and get it right so at the moment my problem is trying to pick people's brains to see if the slight differences I mentioned between the two pistons are going to make a difference after the rebore

As you have got the new piston i would get it bored

Dave

Hi cota 247 pistons don't have a window or port in them ,that sounds like a bultaco piston as well,,,

i havn't used a piston with a window in one would this make the engine noisey ?

out of choice I would use the correct piston,,,,,

cota 247 start at 71MM 237.5 CC this I believe was to get round import taxes

Cota 247 does have a vertical slot in the back of the piston and the earlier Cotas are 247cc using a 72.50 piston. Later models may have been sleeved down as were Bultacos and Ossa Grippers, but not the earlier models. Bultacos don't have a slot in the back of the piston, they have a couple of small holes at the top, but no slot.

My 247 definately has a slot in the back of the piston.Mont and Bulto piston will interchange,i have fitted a 238 bult piston in a cota 242,so i dont think you will have any probs.

I will go in on Monday and get the cylinder bored. My next problem is letting the shop know what clearance I need between the piston and cylinder. I have read somewhere that 247's need 0.085mm and a bloke in the Estates who has worked on many Montesas has advised 0.030mm.

I reckon I may go for an in between figure of 0.050mm which is very close to 2 thou's. What do you people reckon? I don't want to stuff this up as I am down to my last cylinder which can be bored. Thanks

I re-bored my 247 to 00.003 thou, dont know the metric as i only bore in thou.

Dave

Thank you all for that. Had the motor rebored to 2 thou clearance and it is sweet to ride. Started first kick and no probs. Thanks again

At 2 thou let it warm up before you ride it otherwise it may nip up and use a good 2 stroke oil

Dave