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

[blsnelling]

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.

+1. I'm going to sound a little, or a lot, crass here. My Dad taught me...if you're going to do something, do it right, or don't do it at all. There's really no excuse for not checking the squish, and now this. It's not cool and it's not funny. With that said, we're here to help you. Listen to what these guys have to say, and you'll have a good running saw when you're done.

BTW, I still have to remind myself of the same sometimes. It's still good advice though.

 

[davebull]

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.

The carb didn't have a divider when I got my hands on it, I'm not even sure if they have a divider in them.
To my knowledge the divider is in the intake boot but I could be wrong...

 

[davebull]

+1. I'm going to sound a little, or a lot, crass here. My Dad taught me...if you're going to do something, do it right, or don't do it at all. There's really no excuse for not checking the squish, and now this. It's not cool and it's not funny. With that said, we're here to help you. Listen to what these guys have to say, and you'll have a good running saw when you're done.

BTW, I still have to remind myself of the same sometimes. It's still good advice though.

I agree, I did go abit silly and reckless with this project, the reason I post on here is to get feedback from people with a lot more knowledge than me, I've read 100's of threads but you can only learn so much from the theory side of things. Sometimes you've just got to bite the bullet and try it..
P.s I didn't check squish because I didn't have any calipers
Pp.s I do appreciate all the input and I'm always willing to learn..

 

[blsnelling]

No harm, no foul. You took that awful well The divider in the boot can be easily removed. I clip most of it out with diagonal pliers, and then grind it smooth with a burr. Double cut works best. Same with the intake divider.

 

[nmurph]

Aluminum cans are usually .004-.006". Now they might put that 'roo whiz the Aussies pass off as beer in an extra thick skinned can to prevent it from leaking and contaminating everything.

 

[davebull]

It's not all bad only the piston is trashed from what I can see.

I can't see the benefits of using a 272 piston unless you make it a popup.

I'm not running the xtorq boot it doesn't fit the non strato cylinder, but I will cut the divider out of the a/f holder when I get around too it, there could be a benefit with the divider though???

Anyone got any tips on measuring the squish band?

 

[Rudolf73]

Aluminum cans are usually .004-.006". Now they might put that 'roo whiz the Aussies pass off as beer in an extra thick skinned can to prevent it from leaking and contaminating everything.

Lol! First time I've heard that one, but yeah if you are referring to Fosters then your description fits - I think that's the reason we export it, nobody drinks it here.

It's not all bad only the piston is trashed from what I can see.

I can't see the benefits of using a 272 piston unless you make it a popup.

I'm not running the xtorq boot it doesn't fit the non strato cylinder, but I will cut the divider out of the a/f holder when I get around too it, there could be a benefit with the divider though???

Anyone got any tips on measuring the squish band?

Why not just use the piston the BB came with, remove the base gasket and you should be close to .020" or about 0.5mm. Its easy to check, just put a piece of 1mm solder wire in the plug hole and crank it over. If the solder wire is squashed to about half the thickness then your close, but if it turns out paper thin then don't run the saw and fix it - simple as that.

 

[TK]

The carbs came with a divider between the choke and throttle plates. So did the intake - but they obviously don't fit the non strato cylinders. And also the intake. They had to have complete separation of clean air for the stratos and the air to pull fuel through the venturi.

That said, the divider in the intake may not actually be a problem. But, for the best potential air flow I'd remove it in this case.

 

[SawTroll]

Obviously, all deviders will have to be removed.

 

[davebull]

Lol! First time I've heard that one, but yeah if you are referring to Fosters then your description fits - I think that's the reason we export it, nobody drinks it here.




Why not just use the piston the BB came with, remove the base gasket and you should be close to .020" or about 0.5mm. Its easy to check, just put a piece of 1mm solder wire in the plug hole and crank it over. If the solder wire is squashed to about half the thickness then your close, but if it turns out paper thin then don't run the saw and fix it - simple as that.

I know how to check the squish but I wanted to know the best way to measure the squish band in the top of the cylinder to cut a popup from another 272 piston?
I want to make the crown height the same as the BB piston but need to know how far in to cut it?

I'll bolt it up with the BB piston and see how it goes with the xt carb and them compare that with the popup..

Any input is appreciated
Cheers

 

[Rudolf73]

I know how to check the squish but I wanted to know the best way to measure the squish band in the top of the cylinder to cut a popup from another 272 piston?
I want to make the crown height the same as the BB piston but need to know how far in to cut it?

I'll bolt it up with the BB piston and see how it goes with the xt carb and them compare that with the popup..

Any input is appreciated
Cheers

I apologize, I thought you asked for "tips on measuring the squish band".

If you piston is just hitting the top of the cylinder now the that is obviously your zero squish point, now just take 0.020" away from that when cutting the popup and it should be fine.

As for measuring the combustion chamber for the popup, you will need some internal calipers. If you don't have any cut a piece of wire or something similar down to size and use it as a guide.

 

[davebull]

I apologize, I thought you asked for "tips on measuring the squish band".

If you piston is just hitting the top of the cylinder now the that is obviously your zero squish point, now just take 0.020" away from that when cutting the popup and it should be fine.

As for measuring the combustion chamber for the popup, you will need some internal calipers. If you don't have any cut a piece of wire or something similar down to size and use it as a guide.

Sorry my mistake, I meant squish band width.. I'll have to invest in some internal calipers like you said, I'll cut the top down so it matches the BB piston...

If I can get 180psi I'll be happy, but 190 would be better

 

[MCW]

Sorry my mistake, I meant squish band width.. I'll have to invest in some internal calipers like you said, I'll cut the top down so it matches the BB piston...

If I can get 180psi I'll be happy, but 190 would be better

Some of the current 372 BB versions are pulling around 170-175psi compression with base gasket removed. Just make sure you're running a decent set of rings though. Something like Cabers can increase compression over supplied Chinese rings by as much as 15psi.

 

[davebull]

Some of the current 372 BB versions are pulling around 170-175psi compression with base gasket removed. Just make sure you're running a decent set of rings though. Something like Cabers can increase compression over supplied Chinese rings by as much as 15psi.

Ill have to get some i think, I'd be happy with 175 but with a popup I might get closer to 200...
The last (chinese) BB kit I did on a 372 was the same kit and that gave me 155psi with no base gasket but that was without run in so I'd probably gain a few psi after a few tanks

 

[MCW]

Ill have to get some i think, I'd be happy with 175 but with a popup I might get closer to 200...
The last (chinese) BB kit I did on a 372 was the same kit and that gave me 155psi with no base gasket but that was without run in so I'd probably gain a few psi after a few tanks

It changes a fair bit too depending on who the manufacturer was. Some of the early kits I got in were only good for 150-155psi but with the later ones I've seen up to 180psi.

 

[dk27]

Something like Cabers can increase compression over supplied Chinese rings

Any chance you could expand on that thought.

 

[MCW]

Any chance you could expand on that thought.

Certainly can
I import P&C kits and have tested and sold 100's. I had a few issues with some kits using the supplied rings (eg: hooking rings and tearing the tops out of pistons).
I ended up selling my kits with Cabers as I wasn't willing to take the risk and in this process myself and a number of other guys started to see significant increases in compression in the process.
Not all Chinese rings are bad but none are as good as Cabers. For $12 it's a wise fix.

 

[dk27]

Sounds like some cheap compression,thanks for the tip

 

[davebull]

Porting the BB cylinder

Just started my first port job on the BB cylinder, I've order 5 new 272 piston which I'll have made into popups when they arrive.
I'll keep you's posted.....

View attachment 301911

 

[davebull]

Just started my first port job on the BB cylinder, I've order 5 new 272 piston which I'll have made into popups when they arrive.
I'll keep you's posted.....

View attachment 301911

Ok,
I've run into a few more issues, I've bolted it up with the BB kit piston and got 150psi:msp_smile:
Ran it and it seemed good but wasn't getting full throttle I modded the cable to give it that little bit more but while moving the carb around kinked the impulse line:msp_sad:
It got hot and ran a little lean.
I fixed that ran it and ran for a little while until it started knocking and seemed to get worse????

Pulled it down and everything looks fine
Any ideas what it might be?

I'm thinking I may have bent the rod with the 272 piston?? But it didn't knock right away???

Or trashed the bearings from it running lean from the impulse line being kinked but the piston has no scoring???

Maybe piston slap???