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

locky · Guru

Valve stem oil seal replacement.

TTRfan · Super Guru

Hi Locky. You don't let the grass grow under your feet do you!

All four cylinder head bolts should have washers. The two outside ones are often reluctant to part from the head and may not be easily seen!

All valve spring seats have the same part number and are interchangeable.

The piston looks in pretty good shape with very little blowby. Was it at all noisy before the strip down? If not, I would be tempted to give the bore a wipe with 400 grit and just fit a new set of rings., especially as you say there is no lip on the bore.

A rebore is £40 to £50 so not cheap.

Brian

locky · Guru

There was only 1 washer on the outside cylinder head bolts and only 1 washer on the other bolts. It's not a problem as i have some washers exactly the same size.
The inlet valve springs had the correct seats but the exhaust vales had washers ! So i need 2 valve spring seats. Sometime in it's life one of the owners must have assembled it wrong ! I'd love to know why they had the top end off.
I was 50/50 with the piston but the bore looks 100% good and now agree with your comments so i'll order a new set of rings.
The engine wasn't noisy, in fact i thought it was very quiet for an air cooled single.

Do you have 2 valve spring seats Brian ?

TTRfan · Super Guru

Yep - I am sure that I can find a couple for you Locky. Just double checking that you mean part #3 in the pic above?

Brian

locky · Guru

Yes part 3 is what i need (x2). Just been back in the garage to check and they used the cylinder head bolt washers as valve spring seats !!!!Bodgers.
Let me know when you've found a couple and i'll order a new set of rings and a tensioner gasket.

locky · Guru

Is it wise to fit new gudgeon pin circlips or should the originals be ok ?

TTRfan · Super Guru

The advice is to always use new circlips but, as long as there is plenty of "spring" left in the old ones, then they are good to go again.

I can definitely find you a pair of valve spring seats - no problem wink

Brian

locky · Guru

Piston rings, what am i doing wrong. The oil rins won't go in the groove !

edit :) got the oil rings in. The manual states the rings should be fitted with the manufacturers marks and numbers facing up. I can only see marks/numbers on the one ring so i've just fitted it.

Will this be ok ?

-- Edited by locky on Wednesday 11th of February 2015 05:49:46 PM

TTRfan · Super Guru

LOL - I have the same problem with the OE oil rings. Get one plain ring in and then struggle for ages on the second and then it suddenly pops into place confuse

There is only one marked ring, the top compression one. Manual not helpful on that point

Brian

locky · Guru

So the marked ring is the top ring ?

TTRfan · Super Guru

Yep!

locky · Guru

I now have all the parts to finish the top end refresh. I've sprayed the head/barrel with some heat resistant silver.
www.ebay.co.uk/itm/E-TECH-400ML-SILVER-Extremely-High-Temperature-Paint-XHT-VHT-Exhaust-/281016020767

I also spent some time grinding the valves in, im not sure if iv'e ground them in enough, it's been years since i last done the task. Is there any info on this ?

I plan to get it all back together on sunday, i'll post a few pics as it goes back together.

Cubber · Super Guru

The object of "grinding valves in" is to get a uniform seal between valve face and seat face.

Usually start the grind with coarse paste and finishing off with fine paste.

The optimum seating will be a uniform "grey" patch on the valve face that coresponds with a similarly uniform "grey" patch on the seat.

Beware not to grind the valve into the seat and pocket the joint - that's a sure NO-NO.

The width of the seat does not have to be the whole face but sufficient for a seal.

Check the soundness of the finished job by testing with a fluid (thin oil or petrol) in the port.

Martyn

locky · Guru

Thanks Cubber, i thought along the same lines and have a nice grey uniform seal as you describe. I only used the fine paste and spent about 10 minutes on each valve.
Another question. In the Yamaha service manual it states to lubricate the new valve stem oil seals with Molybdenum Disulfide oil , will engine oil be ok ?
And another :) . How should i let the engine bed in after the refresh ?

TTRfan · Super Guru

locky wrote:
Thanks Cubber, i thought along the same lines and have a nice grey uniform seal as you describe. I only used the fine paste and spent about 10 minutes on each valve.
Another question. In the Yamaha service manual it states to lubricate the new valve stem oil seals with Molybdenum Disulfide oil , will engine oil be ok ?
And another :) . How should i let the engine bed in after the refresh ?

I confess to only ever lubing the VSOs with ordinary engine oil. The cam casing gets totally flooded with oil when running and I can't imagine any other type of oil staying effective for long.

With new rings in a used bore/piston assembly I would have thought that taking it steady for a 100 miles would be ample. And just avoid sustained wide open throttle for a few hundred miles after that.

I would be interested to hear views of other owners?

Brian

Cubber · Super Guru

Since your engine runs in engine oil then I guess it should be OK for lubricating the stems.

I think Molybdenum oil is specified because of new valves in new guides with new seals perhaps need optimum chances of getting to know each other. As long as you use it gently, not too many revs and not too long then you should be OK.

As you say, gently bedding everything in (In my Opinion) gives the surfaces more chance to wear themselves together. This is what the "running in" period is all about.

This LINKY gives the general idea about running in - but not ALL mechanics have the same idea.
There are those that say modern materials mean you can wham it from the word go!

I would start using the bike gently at first, resisting any temptation to lift the front, burn rubber and tear about, etc.

I wouldn't labour the engine - but don't race it either. Let it run freely. aww

I would also change the oil at frequent intervals and gently increase the work load over a few weeks.

But then again - others may disagree! confuse

Martyn

locky · Guru

Great advise and info, thankyou both.

locky · Guru

Just another thought, now iv'e ground the valves in it's going to make a difference to the valve clearances. On other bikes to save getting new shims iv'e worked the valve clearances on an oil stone to reduce the thickness. I can't remember if iv'e ever done this to yamaha shims ! Has anyone else done it ?

TTRfan · Super Guru

I have always had plenty of shims to hand to choose from so haven't bothered thinning a TTR shim down.

However, I can't see why not other than if it takes off the case hardening confuse

We probably need a proper engineer to advise at this stage....

Brian

locky · Guru

Finished work earlier than planned today so started to get it back together, everything nice and clean.

Piston and gudgeon pin fitted with ease.

Barrel was a pain to get on, took about 20 minutes.

I started to fit the valves etc to the head and fitted the head and torqued it down.

For some reason my pics won't upload off my phone, i'll post them when iv'e figured out whats happened !!

locky · Guru

Here we go, pics sorted.

Fitted the valves with new seals.

20150214_164505 (1).jpg

20150214_164533 (1).jpg

and the head fitted and torqued down.

20150214_174604 (1).jpg

I fitted the cams and had a swap around with valve shims, i got the inlets to 0.15mm but need new shims for the exhaust valves. I cant find enough info about reducing the shims on an oil stone but i know a few places that are open tomorrow that i'll try.

Cubber · Super Guru

Good work - looks like you'll be getting it nice and muddy by next week. wink biggrin aww

Martyn

locky · Guru

Yes if i can't get any shims tomorrow i'll order a few off Brian, i'll have it finished by wednesday at the latest biggrin

locky · Guru

Valve shims furious . I managed to swap a few valve shims around and i have the intake set at o.15mm, so thats perfect.

The other 2 shims made the exhaust valve clearances so tight that i couldn't get a feeler gauge in.

So i used the 2 inlet shims just to take measurements for the exhaust shims.

This is my calculation(from the chart in the manual). Correct me if i'm wrong.

Exhaust valce clearance should be 0.19 - 0.27mm .

LH exhaust clearance- 0.12mm

Shim fitted 178.

Shim to fit 160 or 165 ?

RH exhaust clearance- 0.12mm

Shim fitted 181.

Shim to fit 160 or 165 ?

I think i need to order 2 x 165.

If this is correct i'll order some shims from Brian.

-- Edited by locky on Sunday 15th of February 2015 02:15:25 PM

-- Edited by locky on Sunday 15th of February 2015 02:17:49 PM

TTRfan · Super Guru

On the cusp - but two 165s would do it!

Brian

locky · Guru

Shims arrived today, thanks Brian great service once again biggrin

New shims fitted and the exhaust clearances couldn't have been better, 0.25mm and 0.26/0.27mm biggrin

Bolted it all back together, turned the engine over a few times just to be on the safe side then fitted the cam cover and everything else.

Fuel tap on, ignition on and pressed the starter. After a few revolutions she fired into life biggrin biggrin

I let it get up to temperature while giving it gentle throttle and it runs real well, i'm chuffed.

It does sound slightly more rattly but i think it's just the valve clearances being slightly bigger, they were all within spec before but to the tight end of the scale.

It seems to be harder to kick over too, must be the new rings doing there job better than the old ones. I wouldn't have thought it would make that much difference ?

-- Edited by locky on Tuesday 17th of February 2015 07:58:18 PM