Yam engine advice

[andy230]

Hello Chaps!

All good points!  Thanks for the input.  I'd be absolutely scuppered without you mob!  YOUR racer, remember?!!

I've posted some pics of the cam clearances on the blog site.  Not too clear, but I think you can still see that its tight, and where its been removed and I need to remove more.

Ive used plasticine with some success, I use a scalpel to cut the plasticine down the centre of the impression left by the valve and then measure with a micrometer. If you dont have a micrometer its worth buying one.

I'll steal one from the old boy when I'm up next weekend!  I dont think he'll be building many more motors...!

(Children are bastards, aren't they?!)

Your also need to measure the squish clearance, its the clearance between the flats on the combustion chamber (front and back) to check piston clerance. Stock rods need around 0.8-1.0mm clearance. 
If the valve-piston clearance is too tight then the pockets can usually be machined.

You will need to assemble with the cam timed up correctly and the chain tensioner fitted, as a small change in timing can quite significantly effect the clearance.

Right... I hadn't thought of this Steve, thanks.  I'll ask Martin Sweet about squish clearance with this (Wiseco) piston on a Carillo rod.

I just spoke to Ash Norrington from whom i bought this motor.  He ran it as a 690 (69 bhp on the dyno with a slipping clutch.  The previous guy ran it as a 640 and then took it out to 690.

This head and cam was on the 690.  Only the barrel (and piston) is different.  The 690 piston has a big "hi-comp lump" on the crown.  (are you loving the technical terms?!)  The new 640 one is flat-topped.  Can we not assume that its ok??  I am assuming probably not as it may bolt down differently, on a different barrel etc...

Boooo!!   Its slow this race assembly!  I'd better get a move on if we want to get it in the frame in January February!

Am really hoping not to have to machine the piston.  And SteveL, I'm really hoping not to throw the head into the bottom of the tank!!

Cheers all, chat soon!

andy

ps.. Any ideas on where to buy plastiguage??  Off to the Electronic Bay!

[Steve Lake]

I don't think it's safe to assume anything when you're pushing the SRX tuning envelope (introducing a bit of modern management speak there)

I had a high comp wiseco on my road bike (the domed one)....and it seemed to me at the time, that the domed bit was well clear of the head.... the dome not rising far into the compression chamber...I'm sure your main area of concern is the valve/piston clearance

[guest27]

If you are worried about compression you can either measure the head volume at TDC and extrapolate from there - or you can bung a compression tester on it and work out the CR from the pressure.  I understand a number of tuners do not worry about CR and actually focus on initially the actual pressure and then getting the bugger to run well.

R

[Steve H]

Static compression ratio is useful as an indication as a like-for like change, but as soon as you introduce different camshaft profiles it becomes less useful. So Andy is running a Stage 4 cam, this will have loads of overlap, reducing the effective (dynamic) CR, so he will be able to run a much higher static CR than a n engine running a standard camshaft.

[Steve Lake]

                              ^
                            ^^^
                          ^^^^^
                        ^^^^^^^
                      ^^^^^^^^^
see........why didn't you know that Andy??

[guest27]

Which I guess is why compression actual pressure is a better measure?

R

[andy230]

                              ^
                            ^^^
                          ^^^^^
                        ^^^^^^^
                      ^^^^^^^^^
see........why didn't you know that Andy??

Ooooh!!!  Scarey.....!

I'll get on with the checking of the squish clearance and the valve pockets.
And I'll speak to martin sweet about what they should be, and about the mythical phosphor washers under the head bolts.

Cheers for now!

a

[Steve H]

Which I guess is why compression actual pressure is a better measure?

R

Yep.

[beeman]

The wisco 640 piston in my srx is about 10.5:1 comp. and is fairly flat topped. Unlike the cosworth piston I had in before which was noticable more domed but gave a 12:1 com ratio (and noticably more pull).
Can't help much more I'm afraid.
Beeman

[andy230]

The wisco 640 piston in my srx is about 10.5:1 comp. and is fairly flat topped. Unlike the cosworth piston I had in before which was noticable more domed but gave a 12:1 com ratio (and noticably more pull).
Can't help much more I'm afraid.
Beeman

sounds like the same beeman...  any pics?  or a part number?

a

[Steve Lake]

G*d almighty! this is a 'simple' one lung motor.....things are getting a bit out of hand here

I mean......next thing will be ...tyre warmers............26 sets of tyres +wets +intermediates

brolly babes (ok, on second thoughts....if you are going to fritter my 6 quid away...then brolly babe it has to be!!)

team manager

suspension specialist

PR person

press liason

OK...I know that most of this is covered by Boyd......but i'm bu55ered if he can be the brolly babe as well!!

[themoudie]

Aye, for Supermono 2008, read MotoGP 2009 with a 500cc capacity ceiling

What goes around, comes around!

Bill.