Couple of questions...

[CH_R1]

Sorry if this has all been done before but I've done a bit of searching and still unsure...

TDM/TRX Motor: Is the only difference between the 270 cranked TDM and the TRX motor the inlet cam profile or are there other diferences (gearing?) Is the TDM 900 just bored out with fuel injection?

From what I can make out the main cause of oil consumption is the valve seals. Is this just cos they are badly made or do the valves/guides wear too causing the seals to fail?

What's the best rear shock option? @ 23,000 miles: a service- oil, seals and possibly new spring or a sub £300 replacement. Can't afford Ohlins/Nitron/Penske, had a duff Hagon (never again), any other mid priced options?

How is the availability of parts? I know after a while it gets hard to find certain parts for older bikes and there comes a point when it's worth hording bits you might need?! (Yoshi Katana exhaust anyone?!) I'm thinking motor parts won't be an issue cos their used in the TDM but other bits will be getting scarce soon.

Thanks in advance!

[slow codger]

Tedium motor and TRX are different motors, Different frame mounting points, Cylinder head and there are others that those that own both will tell you. 900 is a completely different motor, I dont think there is much in the way of changeable parts.
Valve seals will leak oil, valve guides can wear, This also seems to be how they were abused before loving caring enthusiasts got hold of them.
Do a search on rear shocks, I dont think the original can be rebuilt, but other companies do replacements. Mine has done 25,000 kms and the rear is fine (12 stone rider plus gear and on last but one hard setting).
Parts are reasonably easy to acquire, however Yamaha do think they are made of gold, and price them accordingly. Ask on here, its amazing what members hold on to. As above re Tedium parts. Aftermarket parts are still made by some as well.

Dave E

[dandywarhol]

Tedium motor and TRX are the same - I fitted a TRX straight into my TDM and only changed the gearshift cross shaft. I'm told the cam profile is different but I say its the same, certainly the same lobe height - the only differences are jetting/pipes and 1st gear is a lower ratio.

The 900 engine has no liners and has ceramic bores. Yamaha say parts aren't interchangable - I bet quite a few bits are - you can certainly fit 900 barrels to an 850.

I don't think the oil burning problems are mainly valve stem seals - I think its glazed bores through too careful running in.

If you're behind an 850 you can usually smell the oil under acceleration and not on the overrun - that indicates ring/liner "problems" rather than stem seals.

[CH_R1]

Yup, I reckon the TDM bottom end is probably pretty much identical. From what I can make out it seems to be well made with no reliabilty issues so I don't see why Yamaha would want to change it. I wonder if the change to ceramic coated bores has anything to do with the bore glazing issue on the earlier engines? (Saying that, it seems that ceramic coatings are used frequently now by all manufactures so it may have no relation.) Anyway I'm glad to hear that the oil burning is more likely down to glazed bores than worn valve guides/piston rings or whatever. I don't mind topping up the oil a bit more than normal at the mo but would rather not have to think about overhauling the top end for a year or two! Cheers for the info.

[dandywarhol]

The 900 compression ratio is down 0.1 ratio but the cam timing is also different. The opening duration is shorter but the inlet valve closes 9 degrees earlier so that probably balances out the actual compression ratio. Overlap is 2 degres more too.

For any more useless info - just contact me

[dfh]

As far my experience goes the oil consumption thing is valve stem seal related. I had replaced all the inlet valves, new stem seals on all inlet and exhaust valves and new piston rings fitted to honed barrels @ around 85,000 km. For about 5,000km after my oil consumption dropped right down but now it is back to were it was before. I have almost 110,000 km on the bike and it uses the same amount of oil as it did at 25,000km ( just before I did the head the consumption shot right up as the inlet stems stretched). As my bike has never blown oil smoke on start up and has good compression & leakdown figures I recon the oil is not passing the stem seals at rest or it would blow oil like a BMW K100 at start up. Personally I think the arrangement of the 3 inlet valves per cylinder ( they are not perpendicular to the camshaft, especially centre one) means there is more sideforce than usual on the stems and this allows more oil pat the seals as the engine is running, especially at higher revs. The bike is not sucking enough oil past the seals to cause exhaust smoke and my bike does not puff smoke when opening the throttle after long periods of trailing throttle so the rings are sealing well.

The only downside of a TRX's oil habit comes from the complex way of checking the oil level, in the early days a few oil starvation blowups made news but we seem a savvy lot now. There is considerable good that comes from an engine that has this inbuilt top end lubrication, so don't fret.

The rear shock can be modified to improve its performance and it is re-buildable. My shock is fitted with a 650lb/inch spring & I had a Racetech gold valve ( a replacement shock piston & shim-stacks kit) and a Racetech shock shaft seal. Compared to stock its light years better and significantly better than "cheap & nasty" shocks like a Hagon. I also use .95kg/mm front springs & Racetech emulators in the front with good results.

Hope this helps.

DFH

[CH_R1]

Thanks for the info. Can't say I'm worried about the oil consumption personally. I guess it becomes an issue if you're looking to do big miles touring or whatever...I'm really interested in your Racetech rear shock mods - has anyone out there based in the UK had this done? The info I got from Maxton offers replacement springs for the original shock (spring upgrade only- no revalving/reshimming) or a fully adjustable (+ pricey!) replacement aftermarket unit. Your setup sounds spot on...anyone UK based know of anyone offering this?
As to the front- I fitted 0.95kg/mm springs before I'd even ridden the bike cos I'd heard the originals were so far off the mark! Have to say the handling's not too bad given the shocks seen better days. The bike came with nearly new Conti Road Attacks fitted so I figure I'll fit something a bit sportier when they're needing changed and see how we go...
Thanks again for the info!

[dfh]

According to the Racetech website http://www.racetech.com your nearest retailer is

Shock Tech
40 Aylesbury Crescent
Wincobank Sheffield S9 1JR
United Kingdom
0114 243 4226
Contact: Ryan
RYAN@SHOCKTECH.CO.UK
Dirt, Street, ATV
2 mins from Meadowhall, Junction 34, M1

and the UK importer/distributer is

PDQ MOTORCYCLE DEVELOPMENTS
Burnham, Slough, Berkshire SL1,
United Kingdom
(+44) 01753 730043
Distributor & RT Center
http://www.pdq1.co.uk

You may find however that a more local suspension shop is a racetech stockist. When I lived in Sydney I lived about 30km away from the Australian importer and that is where I had the initial build done but when I moved to Adelaide a round trip of 2800km to have a shock serviced seemed a bit impractical. Fortunatly about 5 km away from my house is a suspension shop that uses Racetech gear, and you may well be as lucky. I would phone or email PDQ to find out if there is a local stockist.

However it may well be worth dealing direct with PDQ as Racetech is a US company and the TRX850 was never sold to the septics so there is little actual data on their website suitable for the TRX. The good news is that the shock for the YZF750 is internally & functionally identical (the YZF shock was a different length eye to eye I think and the YZF linkage ratio is different) but PDQ may well be aware that the YZF goldvalve and shaft seal kits are what fit the TRX. When an installer fits a Goldvalve kit there is a code that gives a one off access to the central Racetech shimming database. The one to ask for is the a YZF750 trackday valving... not the race valving. Also with the TRX & YZF leverage ratios differing the recommended spring for your weight is wrong using the YZF chart. For example the Database recommended a 550lb/inch spring but I have ended up after a few spring swaps with a 650ib/inch spring for my 90kg plus gear bodyweight. Another point is that custom spring seats will have to be made for the aftermarket springs as they are both shorter & wider needing custom spring seats made . Sounds complicated but PDQ will do this stuff all the time so I would not worry. I had a quick scan on the PDQ site & a Nitron shock for the TRX is 500 of your boring looking UK beer tokens. The Gold valve kit is 145, shock springs 100 and I would guess the shaft seal about 15 so I expect with labour the deal would be 300 pommy pounds... enough of a saving to buy and fit the Goldvalve emulators for the front forks... with some beer money left over.

Cheers DFH

[CH_R1]

Nice one mate- I'll start making enquiries!