Boxerworks.com

George Ryals wrote:Tim,
The 336 sport cam has a vakve lift of 10.67mm.

On measuring the cylinder volumnes, Why do you want to? Are you trying to determine whether the engine is a 750, or 800, or 900 or 1000. Do you need to be accurate enough to tell if the 750 cylinders have been bored?

Thanks for the cam info. I'd like to know what the displacement is in order to jet the carbs at least close to the factory baseline. That said, the cylinders have small pushrod tubes, so I'm guessing it's either a 750 or 900cc...

Native /5 wrote:

Major Softie wrote:

Native /5 wrote: All true. I was just thinking of getting a very rough figure, then deducing which size the bore was. The volume in the head would likely not put the disp. into the next ballpark.

Yeah, I only made the point because the OP implied with the "highly modified" comment that he could not trust that the bore was anything standard.

How about a comparison with a known standard? Such as Tim's R75/5 that he's been trying to crash.

I only said it's a R75/5, after all these years, who knows what's in there?!

If I were in your position with a highly modified engine, I would pull a head. Not only can you measure the bore, you can check the stroke, the valve sizes and if you take the valves out you can see if the valve pockets have been modified. It would be nice to know if the intake tract and pockets have been hogged out of high rpm only operation.

Yeah, I only made the point because the OP implied with the "highly modified" comment that he could not trust that the bore was anything standard.[/quote]
How about a comparison with a known standard? Such as Tim's R75/5 that he's been trying to crash.[/quote]
I only said it's a R75/5, after all these years, who knows what's in there?![/quote]

Open it up and find out,there may be surprises in there, maybe good maybe not.

Tim Shepherd wrote:I'd like to know what the displacement is in order to jet the carbs at least close to the factory baseline.

Seems like it might be easier to just look at the settings for the 750 or 900 and pick some jets, etc., and ride it. Check plugs, look at gas mileage, evaluate the acceleration, etc. Then adjust from there. Even if you find out what the bore/stroke is, you're still going to have to do some of this in order to get it right. Stock settings are a starting point in every case...then you tweak from there.

Kurt in S.A.

If you pull a head off, measure bore diameter, then length of stroke through one revolution, you can calculate displacement.
Radius of bore squared x pi x stroke will give you volume.

900 parts can be fit right up onto a R75...I'd think R80 parts could fit too, but why bother?
The day I got tossed of an R75/5, I was actually riding an R75/900cc bike...ran like a cheeta.
(Shook like a WET cheeta. )
Maybe look for some part numbers cast into the cyls/heads and see if that's what you have.

Hi Jean, there is "730 1182" cast into the top cylinder fin and 1 and 7 with a small letter "R" next to it on the base, but that doesn't mean it hasn't been bored. Those numbers don't match anything on the fiche.

When I had my 750 bored to 900cc the machinist changed the 7 on the bottom of the barrels to a 9, so that everybody would know what they were working with.
Apart from pistons, rings and gaskets nothing else needed changing, but if you have a highly modified motor and seek reasurance just get it onto a dyno, they will optimise the timing and let you know if the carburation needs optimising.

Curiouser and curiouser, on another website it was mentioned that the 336 cam had the same lift as stock, but longer duration. Can anyone confirm this?