372xp with 272 piston in BB kit.... Yes it will work

[davebull]

[SUP][/SUP]
Just finished rebuilding my 372 with a 272 piston in a bigbore kit, had the use 2 base gaskets so the saw would turn over
Other mods include a 372 xtorq carb which is larger than the standard one to cope with the 76cc's
View attachment 300660

 

[davebull]

YouTube

Here a vid

 

[mountainlake]

Sounds snappy. Steve

 

[davebull]

The xtorq carb seems give better throttle response compared to the older carbs, haven't had a chance to cut with it yet it might go....KAPOW!!!!

 

[barneyrb]

22.5 compression height on the 372 and 24mm on the 272.....1.5mm is about .059" so I would be checking squish real close........

 

[blsnelling]

Do you have access to a lathe? Just cut a popup in that piston and ditch the extra gasket. You'll gain compression and a little intake duration.

 

[A.E. Metal Werx]

So how much would you take off the top of the piston? Or better yet give us the calculation to figure it out based on differences in manufacturer tolerance.

Is that a serious question or a leg puller?

 

[blsnelling]

So how much would you take off the top of the piston? Or better yet give us the calculation to figure it out based on differences in manufacturer tolerance.

We would have to know the existing squish measurement, and the thickness of the extra gasket.

 

[w8ye]

It would also depend on the amount of material in the top of the piston and the distance from the top ring land to the top of the piston.

 

[SawTroll]

The xtorq carb seems give better throttle response compared to the older carbs, .....

No surprice there - it is a larger carb!

 

[A.E. Metal Werx]

Just wanted to see how many people would invest the time to write it down. Motocross! I used to do that in the late 60s and early to mid 70s What kind of bike do you race? 125, 250 or open? My experience was open Husqvarna 400s and 360GPs.

When I was serious racing I was on a rmz250f with all the engine and suspension work that could be done. Sold it off and bought a bone stock yz125 and sent the motor to Eric gorr for his porting and 144 kit. Super fun bike. I have since put mx to the side but with a little boy due in late July I'm sure I will pick it back up soon. As in sure you know, it's a hard sport to quit completely.

 

[davebull]

Do you have access to a lathe? Just cut a popup in that piston and ditch the extra gasket. You'll gain compression and a little intake duration.

No... I haven't measured squish I see myself as abit of a gambling man, but I reckon it would be just about kissing. I think I go with what your saying brad and cut a popup, I was thinking of taking 1.25mm of the top of the piston the width of the squish band and not running any gaskets?... But what is the width of the squish band?:confused2:

I'll pull it down today and check for any damage and post some more pics

 

[w8ye]

The width of the squish band to cut in the piston?

Look at the width of the squish band in the head?

 

[davebull]

The width of the squish band to cut in the piston?

Look at the width of the squish band in the head?

My eyes aren't measuring devices...... I was hoping for a figure someone already has, I haven't got the tools to measure.

I think I'll just take the lot to my machine shop and they can work it out

 

[davebull]

Pulled it back down and this is what I found.....

View attachment 300755
The crown looks like it may have had contact..


View attachment 300756
I think the intake port maybe a little sharp

View attachment 300757
It's a little hard to check squish when it doesn't exist

View attachment 300758
Xtorq carb setup

 

[davebull]

Dam iPad, stupid upside down photos:bang:
You might have to stand on your head to view some of these...

 

[w8ye]

I can sure see the squish band in that cylinder head

 

[davebull]

I can sure see the squish band in that cylinder head

Your very observant... There is a squish band but no squish because the piston was hitting the top of the cylinder:bang:

 

[RiverRat2]

Your very observant... There is a squish band but no squish because the piston was hitting the top of the cylinder:bang:

Yeah!!! It got squished all right!!! is that cylinder cracked????

 

[TK]

Did you pull the divider out of the carb? Only reason I ask is the one in the a/f holder wasn't cut out.