Turning off material on airhead barrels. Who does it?

[mattcfish]

I'm looking for a machine shop that has experience turning material off the base of airhead barrels.
Preferably close to Western Washington. Looking to do a comp increase without modifying the heads.
Does anyone have some experience with this?

[sprints@pldi.net]

You can also have a cnc shop face them off in a mill - Just clamp it through the center and circle interp the flange - I that sort of stuff everyday

[mattcfish]

Seems simple enough. I just need to find a machinist who wants to do it

[mattcfish]

There used to be a guy right here in Bellingham, WA that could do it. He passed away last year, so far no luck finding a machine shop that will touch it.
Any Seattle Airheads out there that know a machine shop that can help me out?

[Ken in Oklahoma]

I'm thinking that any competent machine shop could do it. I gather that we are talking about reducing the diameter of the barrel spigot that goes into the block. I suspect that the hardest part of the job would be getting the barrel truly square and centered on the lathe chuck, presumably using a 4 jaw chuck. The top of the cylinder, which presumably would bear against the chuck, would need to be square to the cylinder bore. Since the lower flange on the barrel was (presumably) square when the cylinder was first machined and (again presumably) the top of the cylinder was square with the lower flange I would not expect the job to be as demanding as if shimming and such were needed to square the cylinder to the chuck.

Hopefully that made some sense. And hopefully I'm not full of (fill in the blank). And hopefully, yet again, I've interpreted the 'need' correctly.

Ken

[Kurt in S.A.]

What does all this do to pushrod tube lengths? What about the four head bolts? Will everything still fit?

Kurt in S.A.

[ME 109]

I gather that we are talking about reducing the diameter of the barrel spigot that goes into the block.
Ken

No Ken, reducing the length of the barrel (so to speak) to increase compression.

[mattcfish]

siebenrock stepped piston.jpg (72.54 KiB) Viewed 2805 times

I gather that we are talking about reducing the diameter of the barrel spigot that goes into the block.
Ken

No Ken, reducing the length of the barrel (so to speak) to increase compression.

Exactly. I want to increase compression without messing with the heads. I have R90 heads and stepped 1000cc Siebenrock pistons. This is the prescribed method in the famous german 336 bulletin. I can't find a link to it anymore, it used to be here http://moragafalconers.org/BMW_336_Cam/ ... 0Draft.pdf
If I milled the heads The stepped area outside the R90 squish band would remain at 2mm while the inner portion of the piston band would get tighter. This would force some of the charge the wrong way. Machining the base of the cylinder makes everything come together evenly.
It may change the PR tube alignment very slightly, but I think there is quite a bit of wiggle room there.
I wnat to bring the compression ratio up to a little over 10:1 from the current 9.5:1. According to the bulletin, removing just .5mm should do this, but I also want to be able to use the R90 base shims with my small spigot Siebenrock barrels.

[Kurt in S.A.]

How will you handle the increased compression with fuel in order to prevent detonation? If you're going to do this, I think you need to dual plug at the same time.

IMO there's only so much you can do to these engines to make them perform better. Often times, you may have to throw a lot of money at it to gain only a small percentage of performance. Not sure that's really worth it.

Kurt in S.A.

[mattcfish]

How will you handle the increased compression with fuel in order to prevent detonation? If you're going to do this, I think you need to dual plug at the same time.

IMO there's only so much you can do to these engines to make them perform better. Often times, you may have to throw a lot of money at it to gain only a small percentage of performance. Not sure that's really worth it.

Kurt in S.A.

Already dual plugged. No sign of a ping at 9.5:1 even with regular gas. Running a 336 cam, great performance.
Need to fix an oil leak at cylinder base, so thought this would be a good
Time to do this. The 336 does lower compression somewhat because of overlap.
Runs nice where it is, but most recommend going up to 10:1 and beyond for most efficient power output across the range.