Yamaha TRX850 Enthusiasts Forum

Can't do too much until the big valves arrive next year (and it's perishing in my unheated workshop ),so decided to get the cams I'll be using so I can hit the ground running.



These are the Kent Cams "Yam 9" grind that "everybody" gets and uses in a Trx.I think they'll prove to be just the ticket for my quest for a packed mid-range.

While I'm here I thought I'd try to clear up the issue of the quoted timing figures.I have read on the forum that the timing figures for this cam are, Inlet 15/45 and Exh 49/11 (and so they are) but they cannot be directly compared to the std Trx quoted figures of 29/59 inlet and 49/11.

The Yamaha cam durations are quoted "seat to seat" whilst the Kent cam durations are quoted at .040" lift.
If this were not the case the numbers would imply that the Kent inlet cam has only 240 degrees duration (15+180+45) compared to the std Yamaha cam with 268 degrees (29+180+59).Clearly nonsense .

After speaking to the designer of the Kent cams,I established that the "seat to seat" figures for this grind are in fact; Inlet 45/75 and Exh 79/41 making 300 degrees duration for both inlet and exhaust .
This is some 32 degrees more inlet duration and 42 more exhaust duration than standard.
These cams also have a lift of 0.43mm more for inlet and 0.28mm more for exhaust.

Can't wait to have completed head to fit them to


Mark.

Now that's funny; looking for TRX cams and Google gets me here.. surprise!

So, if I order TRX cams by Kent I will get the above mentioned ones?
Are your cams modified standard ones or do they make them new?
I have no idea how this works anyway.

Hi,

Yes they are reground original Trx cams. I'm sure I posted all the relevant information with the photo.They are designated YAM 09 AND extremely widely used by Trx modifiers in the UK.
They will produce a powerful but not peaky engine when used in conjunction with FCR's a ported head and higher compression ratio.

Good Luck,

Mark.

I know these cams are widely used but the part I didn't get is the 240 / 268 / 300 degrees.
Now that I read it again (and again...) I understand that the figures were not comparable.
So the YAM9 cams are not changed itself but the way measurements are done to get the figures you quoted.
Sorry, it is just that this isn't my native language.

I applaud all you European members who use English as second or in some cases a third language

In the UK there are many people who can't even spell or write properly in English

If you want cams to produce a fast road (and trckday) engine,these are the cams you should use.
If you are building an engine purely for race purposes with big power at high revs then I would recommend using billet cams. These are 3 times or more the price of reground standard cams.
They are able to give much more lift though and can still be designed with moderate durations for road use (if required).

I would expect a well thought out and built engine with ;

High lift billet cams
Big valved ported head
878cc (or more)
FCR 41 carbs
Akra or similar exhaust with larger diameter headers
and a good programmable ignition to easily produce more than 105 bhp at the wheel.

I am presently working on a second cylinder head that may or may not receive billet cams in the future as I now have another TRX.


Mark

I already have TDMR flatslides and Akra headers.
Next step are the bigger valves and flowing (that's the same as porting, right?) the cil.head.
I'm aiming on cams too, as you already noticed.
Because of the oil consumption I'm looking for 1mm oversized pistons. This is cheaper than a bigbore kit. Also, I heard a little bit too often about broken conrods and stuff like that with the bigbore and race cams combination.
With all this I think my TRX becomes a very nice trackday tool without spending to much €€'s. Although the misses would not agree about the last part.

Sounds a good specification to me

Fitting cams with long duration that make all the power at very high revs (for a TRX ) encourages the rider to search out the power and this is when rods seem to break. It all how much power you want and how much you are prepared to spend to obtain it with reliability.

I personally woudn't fit a long duration billet cams without first fitting better
quality con rods.

Using a moderate cam grind such as Kent's YAM09, won't need high revs (for a TRX ) to make nice power.

Hope this helps,

Mark.

Okay, today I found out that oversize pistons are not cheaper than a bigbore kit ( 878cc, Kedo).
Now I'm wondering if bigger valves, Kent cams and mentioned bigbore kit makes the need for better conrods? Any idea's on this? And were do you get these conrods anyway nowadays...

Tarwetijger wrote:Okay, today I found out that oversize pistons are not cheaper than a bigbore kit ( 878cc, Kedo).
Now I'm wondering if bigger valves, Kent cams and mentioned bigbore kit makes the need for better conrods? Any idea's on this? And were do you get these conrods anyway nowadays...

A bike modificator once said to me, revs kills conrods not low down tourque.
You´ll be fine with the standard, no over reving though!

Killerwhale wrote:
A bike modificator once said to me, revs kills conrods not low down tourque.
You´ll be fine with the standard, no over reving though!

Okay that's good And makes sense.

Funny thing is, that piston sizes are quite close together:
Original 89,5 mm
1st oversize 90,0
2nd oversize 90,5
Bigbore 91,0
Tdm900 92,0

But i guess you can just drill the cilinders up to 91mm? Since there is no nicasil or stuff like that involved.
It would be nice to drill the original cilinder up to 92 mm and simply use original tdm900 pistons but that sounds too easy, so I think it does not work like that.

Pretty sure that going to 92mm bore would leave the liners too thin. There is comment elsewhere on the forum confirming this and that 878JE is the max safe oversize (without resleeving perhaps?).

I have not changed my rods (878, FCR, AKRA) but I never rev beyond 8krpm. So far so good even with track use.

What I will do this winter when I strip the motor is get the rods shot peened. Cheap process but as I understand it, this must be done correctly or you can introduce horrible residual stress into them.

My old 80's CB900F proddie racer (remember them?) had RSC998 High Comp pistons and I used to almost rev it through the red (in my exhuberant youth) and though CB900's were reknowned for throwing rods, it stayed in one piece. When I did whip the head off there were 4 neat dents in the top of each piston from valve bounce but it never bent any of them. This motor staying together convinces me that peening is an effective process.

Has anyone else any experience with shot peening?

As far as I am aware, I am the only reported con rod failure on a TRX engine - that was in 2006 on the way home form Le Mans 24 hours. No idea why or how but the con rod let go and my piston smashed into the head fubarring the engine.

That was when I built an engine with pretty much the spec you suggest above (making 103bhp). I then did many miles on it (road and track) with standard rods. Rebuilt on a number of occassions to check the rods and all was good. And I know lots of others who have tuned and used standard rods.

If you are so inclined Carillo make rods for the TRX (v rare and expensive) and over made some Ti rods (v v rare and v v v v expensive)

There was this other lad, who raced his topnotch-tuned TRX... Not too long ago!

SpondonTRX also suggest stronger conrods:
viewtopic.php?f=6&t=8649#p88857

Another thing to consider. You cant use tdm 900 pistons with trx rods, the tdm pistons have a bigger wrist pin. TDM rods are stronger than trx rods also.

Nice to hear that 900 rods are stronger but is this just heresay or has anyone actually tested them and found this to be the case?

I've never heard (yet) of anyone building a motor poducing sustantially more power using Tdm900 rods and the revving it to 9000rpm.

I'd be happy to hear a lot more substantive information to back up this claim.



Mark.