Am I missing something?

jakepeewee

Hi all.

I am finally making progress with my bike, but am encountering something I wasn't anticipating.

My engine is build up with S4 crankcases and 748R heads (and some other internal stuff) but now that I put the engine in my 851SP3 frame, I am having problems installing the radiator.

At the top of the radiator the most forward injector is touching the fan, and at the bottom side the fan is touching the horizontal head.

I checked the height of the 748R heads, they're the same size as the OEM SP3 heads. I can't imagine that the (12 mm) mounting holes in the S4 crankcase are repositioned?

Am I missing something?

Regards,
Jacco

workslorenz

748R heads have a lower position where the inlet manifold face is bolted... so if you installed the standard 888 inlet manifolds the throttle body is in a different position then standard.

outtacontrolla

workslorenz wrote748R heads have a lower position where the inlet manifold face is bolted... so if you installed the standard 888 inlet manifolds the throttle body is in a different position then standard.

Works lorentz is right the 748R heads are machined down and use different inlet manifolds , I'm surprised you got the std throttle bodies on there .
Perhaps you can jiggle the pipes around or move the fan ?

jakepeewee

hmm, I did use the original inlet manifolds and it did take some effort to install the throttle bodies. What do you mean by machining down the heads? Where is it machined?

I can understand that the lower position of the inlet manifold and thus the throttle bodies could cause a conflict with the fan at the position of the most forward injector (of the 4). Down low though the radiator (fan) also touches the horizontal head? That conflict is not related to the different inlet manifold I think.

I probably need to move the radiator a bit further to the front of the bike, 1 cm?, hope that doesn't create a problem between the wheel (travel) and the radiator.

Thanks all for your help, great info on the 748R heads!

jakepeewee

I just checked the installed 748R heads. Compared the position of the bolts for the intake manifold (distance from the top of the 748R head) with that on my SP3 heads. As far as I can tell this position is the same, as is the total hight of the heads. Still a bit confusing.

griff851

Not sure if this helps. Just did a quick goggle The fan is over to one side and fairly flat on the 748r according to this ebay pic.

griff851

It's now been about 12 billion years since I worked in the shop, but I seem to remember chatting about 748r heads and a problem they had in relation to the very high valve inertia. Something that monitoring would be needed, ie valve clearances regularly. Which you do if your racing anyway. A lot of lift on those babies. Brad has probably seen more of them in the shop, he'd know.

griff851

Ps, please send donations to Griffy still needs tires fund @damn it .com. My son is a national level 10 gymnast, and you think playing with bikes is expensive. Nope!

brad black

some single injector throttle bodies will fix one issue.

jakepeewee

Think the issue with the injector might not really be a problem, down low is the bigger problem.
Probably going to cut part of the fan to get some distance between the head and the fan.