A forum for owners of Yamaha TTR250 trail and enduro bikes!

Flying Dodo · Veteran Member

Piston rings, valves etc.

TTRfan · Super Guru

There are a few piston pics on this thread.

Make sure you have the piston ring gaps placed correctly as show in the manual extract below:

piston and rings.jpg

The manual suggest that all the rings may have a mark. In practice it is only the top compression ring that has this mark!

The oil control rings fit the piston more snugly than the top two compression rings.

Some help on cleaning up the valves here

Brian

Flying Dodo · Veteran Member

Thanks Brian,
Will see about taking it all apart again next week and doing it properly including the valves - they needed a clean really anyway, and yes I missed the bit about the positions of the ring gaps so can redo that at the same time - hopefully the gaskets will be re usable for the cylinder block and head. Ah well back to the drawing board. Do I need any special tools if I take the valves out - to do it or put it back? and is there something like your magic oscillating tool available anywhere?
Thanks
Dave

TTRfan · Super Guru

An example of the valve tool on eBay here

It is useful to have a proper valve spring compressor tool set - maybe you could hire or borrow one for the job?

Flying Dodo · Veteran Member

Thanks Brian
They seem cheap enough on e bay and there's no chance of borrowing one here in France.
Looks like I'll have to give the credit card a bashing when I'm over.
Thanks

Fladdem · Senior Member

I assume you have access to a compression tester? If so, squirt a TINY amount of oil down the spark plug hole, the oil should help seal the gap between the rings and bore, if compression increases, it's rings, if not, it's valves. Unless you have already done that, in which case, this could be a waste.

Flying Dodo · Veteran Member

Thanks Fladden, will give it a try

Flying Dodo · Veteran Member

Hi Fladdem

Lots of pressure with oil in the bore so assume it's the piston rings also a mark on the top of the piston where one of exhaust valves appears to be sticking and catching it

Will get ordering new rings and a couple of valves and springs.

Thanks Dave

TTRfan · Super Guru

If a valve has been hitting the head then it's worth checking it's guide.

Occasionally this can crack the valve guide - usually only when the piston has given the valve enough of a whack to bend it!

Fladdem · Senior Member

Piston rings aren't expensive, but might as well reduce the costs as much as possible. :) Like if you changed rings, then the compression was still low, you'd be annoyed. Is it a deeper mark than usual? My brand new Wossner piston came with valve grooves already in it, for where the valves would sit. If it's definitely from a valve touching, you are lucky that is hasn't trashed the head or con-rod.

Could the valves just need re-shimming? Cheaper than new valves, if so, a new shim under the valve bucket should lift the valve up and away from the crown. Have you measured the clearance between the camshaft lobes and the tops of the valve buckets? If so are they in spec?

Also, do you have a service manual? I love mine and couldn't do without it. I printed it all off at college one day, the 300 odd pages, then went through and holepunched them all and stuck the pages in a folder. I believe Brian has a link to a download on one of his pages. This should tell you how to dismantle the head and get the valves out.

Chasbmw · Newbie

TTRfan wrote:
There are a few piston pics on this thread.
Make sure you have the piston ring gaps placed correctly as show in the manual extract below:
The manual suggest that all the rings may have a mark. In practice it is only the top compression ring that has this mark!
The oil control rings fit the piston more snugly than the top two compression rings.
Some help on cleaning up the valves here
Brian

Brian,

ive had a query from some friends who are currently re ringing Lois Price's old ttr250 which is in Bulgaria.

they have obtained a replacement set of rings that has come in a Yamaha loggoed box from Germany.

what has stumped them is which ring goes where?

oil ring. Obvious

a dark metalled ring, marked RN

chrome coloured ring, beveled top and bottom but no marks.

they were going to fit the dark metalled ring in the middle, with RN upwards and the chrome met talked ring in the top position, is this correct?

many thanks

charles

TTRfan · Super Guru

Chasbmw wrote:
TTRfan wrote:
Snip
The manual suggest that all the rings may have a mark. In practice it is only the top compression ring that has this mark!
The oil control rings fit the piston more snugly than the top two compression rings.
Some help on cleaning up the valves here
Brian
Brian,

ive had a query from some friends who are currently re ringing Lois Price's old ttr250 which is in Bulgaria.
they have obtained a replacement set of rings that has come in a Yamaha loggoed box from Germany.
what has stumped them is which ring goes where?
oil ring. Obvious
a dark metalled ring, marked RN
chrome coloured ring, bevelled top and bottom but no marks.
they were going to fit the dark metalled ring in the middle, with RN upwards and the chrome met talked ring in the top position, is this correct?
many thanks
charles

Hi Charles

Interesting to know that Lois's TTR is in Bulgaria!

The manual is a tad misleading in that only the top compression ring has a marking. So the ring with the RN marking goes on top with letters facing the head.

I hope their rebuild goes well!

Brian