The TDM 900 conversion....

[Killerwhale]

Hi Guys,
A constantly discussed thread, so here are some real answers.
First, I did all the work myself, not took it to a local tuner so these are real facts not just opinions or heresays. The reason was the engine was using a lot of oil, the barrels having worn on a sideways axis, not front to back. Taking into account not having to get a rebore done, the cost was about £150 more than a re-bore to 878cc
Second, this was my way, not the only , but it works and has been in the bike for 2 years and about 15,000 miles and proved reliable.
Parts required.(prices approx)
TDM 900 Barrel =£200
TDM 900 2x pistons, rings, gudgeon pins, circlips, = £200
TDM 900 camchain tensioner , = £30
TDM 900 head and base gasket, =£35

Con-rods need to be removed from engine to get little end reamed out 1mm O/S. Engine can be left in frame.
If the sump is taken off you can use a 3/8th drive socket with a waisted extension to reach the big end nuts, (just, with a bit of fiddling, and turning over of crank) 13mm nuts if memory serves me.
Get the rods reamed to your new gudgeon pin dia.
The head on the TRX cannot be skimmed much to raise compression, because the valve seats are nearly flush with the head surface.
The TDM pistons are concave and a lower compression ratio than the TRX.
So, to get a good squish, which is all important, I took ( I think, but will check ) 20 thou" from the top of the pistons and the BASE of the barrel.
Some more could come off but I wanted to start from a safe position. It is very hard to measure compression ratios using oil, hydraulic fluid , etc because of the viscous effect of the oil, and just 2 or 3 cc could make a whole point difference on the comp. ratio. Mine measures about 10:1 approx.
Then stick it all back together!
The valve timing will be retarded slightly, I don't know if it makes a significant difference, but I slotted my cam sprockets and set the cam timing to Mr Yam's std. marks.
I am measuring the lobe centres at the moment for a base line, then will compare the V2 cams . It is standard practice to measure cam timings at 1mm lift.
So in a couple of weeks we and Mr Phuk will be able to swop notes.
If you need any more info just ask, I wish I had the info before I started

[wicky]

Hi Killerwhale,
those words look very familiar are they yours or Rick 900's i was interested to know if it's possible to get flat topped pistons for the conversion , which would save alot of time and effort messing about with skimming a few thou off the bottom of the barrels or would you still need to do the skimming anyway to raise the compression some more ? regards Wick

[phuk72]

I looked into putting a complete 900 engine into my TRX when I blew my last engine. In the end I went TRX route plus big bore.

One of the reasons was the lack of after market pistons for the TDM900 - so it's standard or nothing!

[wicky]

I looked into putting a complete 900 engine into my TRX when I blew my last engine. In the end I went TRX route plus big bore.

One of the reasons was the lack of after market pistons for the TDM900 - so it's standard or nothing!

true enuf, an aquaintance (spellin?) has a TDM 900 tooned up and bored out to 960cc, i wonder if his pistons are flat topped ?? oil have to ask the question i supppose !

[Kirk]

I've heard of the 960cc kit too, from TTS in ol' blighty I think. If the 960 kit goes into the 900 barrels, and the 900 barrels go into the 850 bottom end/head, surely this would be worth looking at? And surely if its an aftermarket kit they would get specific pistons to suit, which would presumably be hi-comp?
From what the guys have said about the difference with the 878 kit, and from the difference in power and torque between my old 650 guzzi compared to the 850 trx, going up 110cc on the 850 would be well worth the effort.
Thoughts?

[phuk72]

If there is such a kit available it wasn't around a year ago and isn't on the TTS website (and Google throws up a blank).

Have to say there isn't a huge tuning market for the TDM900 and I find it hard to believe that anyone would want to big bore the bike and destroy the ceramic lining (having this reapplied to the liners gets expensive). Higher comp pistons I can understand but these aren't around?

Maybe someone has made some as a one off?

[wicky]

If there is such a kit available it wasn't around a year ago and isn't on the TTS website (and Google throws up a blank).

Have to say there isn't a huge tuning market for the TDM900 and I find it hard to believe that anyone would want to big bore the bike and destroy the ceramic lining (having this reapplied to the liners gets expensive). Higher comp pistons I can understand but these aren't around?

Maybe someone has made some as a one off?

me aquaintance has just that, he had it done at TTS, they reapplied the ceramic coating like you said PHUK, carillo rods specially made up too, gas flowed head, power commander, air box mod done too, etc etc, funny thing is when TTS sent it back to him there was alorra "piston slap" so he had to send it back again "to do it right second time round" me udder buddy did the same to his TDM 900 too but he opted to leave the bore size standard. i don't thing TTS advertise it cos it's not the type of bike that many people are going to lavish alot money on. i tried the TTS modified 900 a few weeks ago...........very quick imo, im yet to try the 960 version though

[phuk72]

Holy shit - knowing what TTS charge ......

[wicky]

Holy shit - knowing what TTS charge ......

well i know that one guy spent about £2,500 on his enjun job !! the guy with the 960 conversion i reckon has spen alot more though, ohh to have plenty of money

[wicky]

update; i have managed to get 900 barrels, pistons & rings, con rods, cam chain tensioner & guides all ferra song interestingly? enuf the cam chain guides are the same part number on XTZ750's, and all TDM's & TRX's. all i need now is the money to pay some willing clever bod to measure, skim, shave and fit it all fer me

[phuk72]

i have managed to get 900 barrels, pistons & rings, con rods, cam chain tensioner & guides all ferra song

How much then? All new?

[wicky]

i have managed to get 900 barrels, pistons & rings, con rods, cam chain tensioner & guides all ferra song

How much then? All new?

allegedly only done 3000 miles, the barells, pistons and big end journals look immaculate so it may well be true. £200 + p&p.

[phuk72]

A song? That's a steal

[HansJ]

Think I'd better add some more info from that thread, as I just skimmed through it.

All courtesy of Rick from the old forum! Earywig seemed to have the before/after dyno charts, any chance of getting them?

"Hi Guys,
Just got my "Book of Words" out with all the mods,, so I can be more specific.
Took .25mm off barrel base and piston top, to get a squish of approx 1mm. I say approx because of piston rock in the bore.
Because the TDM piston is so dished/concave, it is only in the ring lands area that metal is removed.
The compression is approx 10:1, for the aforementioned reasons, plus I did a lot of dry measurements, rather than build and strip the motor and wasting gaskets.
The squish could be narrower and the comp ratio higher, but I want the engine to reach the top of the highest Alpine Passes and use cheap French petrol at the same time . No knocking/pinking in this tune.
The base gasket needs a trim, use scissors, to match the trx one , in places. There are no rubber O rings for the barrel as it is a Chrome liner.
That is how Yamaha managed the bigger bore, by not having sleeves to fit in the barrel. No work to do to make the c/cases and barrel fit.
The TDM only has a 6 speed gearbox in it's favour, what with the Electronic injection and the flap to change the airbox velocity, plus meeting latest emission laws, it seems to be in a soft state of tune.
Brit bike mags give it 72-76 bhp, back wheel.
I have my V2 cams to fit, interestingly they have virtually the same lobe centres as Phuk 72's Kent cams.
Vee2 inlet 108.5, ex. 104
Kent " 109 , " 105,
As good as the same.
Just looked at my dyno figures, it gave about 7lb-ft more torque and 6bhp with the 900 kit. Max power at 7,000 rpm.
And my revcounter was reading 500 rpm faster than accurate..
So to recap, a "big bore" doesn't give much more power but it does help mid range, and yes it can get expensive but I just like playing with engines.
Simple as that.
I haven't worked out how to send pictures yet, but I have pics of the 900 barrel and pistons and c/case which help explain it all. If someone gives me their E-Mail adress I will send them, then that person could post them here
Cheers,Rick"

"Hi Ike,
Why no Dos Boy now??
Complete piston , rings and gudgeon pin weigh same for both.
No problems there
Used head and base gasket from TDM, look better quality design, more metal than fibre.
TDM Head gasket has bigger I.D. (obviously), can't remember any other differences, but they don't leak 15,000 miles later, so thats fine.
Another thing with Compression ratios, don't believe the quoted ones.
Measure your own, mine was 10:5-1 approx, but you could try more comp. by taking more of the barrel base and piston top.
reading my notes again, I have a min. of .8mm squish and max. of 1mm,
so room to play.
The head volume is 33cc.
Thanks to Citroen 54 for posting, pics, hope Earywig isn't too busy at work.
Rick"

[Quan-Time]

just do what i did.. put TDM900 pistons (forged) into trx850 block.. Sure i put custom sleeves in there.. but i can assure you that it fits fine..



Thats TDM900 pistons in a TRX850 block and head that ive cleaned up.