Boxerworks.com

Can I add another dimension to this thread, please? I had removed the pushrod tubes from the cylinder to do some valve work and "forgot" to take measurements of the amount that the tubes were pressed into the head (measured from cylinder flange to the top of stop ring). I don't know the history of these heads so I don't know whether they did seal in their previous application.

Like many others, I am not a friend of using the mentioned "tool" to set the depth if can get it right the first time. Is there a dimension for the distance between cylinder flange and stop ring for a /5 head with 0.020" base gasket? Has somebody measured it? Was there a different depth for /5/6 due to them engines using cylinder base gaskets?

Thanks and sorry for the hijack.

Stephen

Stephen -

I don't know of a specific measurement, but Oak provided a diagram that showed the location of the stop ring on what was probably a cylinder with no gasket. Basically, if you take a straight edge along the bottom flange of the cylinder (the part that butts up against the block), that straight edge should just touch the stop rings. Note that the stop rings will be canted since the tube is running at an angle. But only a small part of the stop ring should touch the straight edge. I suppose if there was a gasket involved, then the stop ring would need to be a small bit closer to the block and the straight edge would touch more than just a small point on the stop ring.

When I put Siebenrock cylinders on my R100/7, I checked this on the already assembled cylinder. It was correct. I probably goofed a bit in that I used a 0.67mm base gasket to lower the compression ratio...I didn't not adjust the stop rings.

Kurt in S.A.

Kurt in S.A. wrote: Oak provided a diagram that showed the location of the stop ring on what was probably a cylinder with no gasket.

I couldn't find that ... do you have a link?

No link...Oak doesn't do pictures on a website. He sent me an email with a PDF file. I then took the picture and created my own PPT picture which shows the same thing. His art...I didn't want to pass it around the world. But basically it's as I described...hopefully that was clear enough.

Kurt in S.A.

Sorry, Kurt, I don't get it. We must be talking about different things. I am looking for a number # in either inch or millimeter for the distance between the stop ring and the cylinder, preferably on a /5. I can certainly add the 0.022" for the hi-comp base gasket.



Hope that picture helps.

Stephen

Right...talking about two different things. But it would seem that as long as the tube is positioned far "enough" into the head, the more critical dimension is what I was describing. In other words, you want the stop ring to be the right distance from the block so it puts the proper squeeze on the seals. Some of the stop rings are movable...some weren't...I can never remember which years. For the brazed on rings, the only adjustment for the stop ring is to reposition the tube within the head.

I have my old /7 jugs at home...I could measure those.

Kurt in S.A.

Kurt in S.A. wrote:But it would seem that as long as the tube is positioned far "enough" into the head, the more critical dimension is what I was describing. In other words, you want the stop ring to be the right distance from the block so it puts the proper squeeze on the seals.

Yes. And that is exactly my predicament: how far into the cylinder to create proper pressure on seals?

Measuring a /7 could indeed help, so please measure those if it is not too much to ask.

Thanks in advance, Stephen

Not the consistent numbers I would have thought. I measure like you showed...from the underside the bottom fin to the top side of the stop ring. Here's what I have (in mm):

Left cylinder - 84.90 (exh) and 83.75 (int)

Right cylinder - 84.14 (exh) and 84.13 (int)

I can tell that the left exhaust stop ring was moved based upon the "clean" area on the tube. While I don't like doing it, I did attempt to push the ring down and this is probably the one I did. I can't explain the shorter distance on the left cylinder. The right cylinder looks pretty consistent on both. Maybe that's the "nominal" numbers for the /7.

Kurt in S.A.

Thanks, Kurt.

My measurement are all around 95mm on the /6 cylinders, 82mm on the /7 cylinders. Both stop rings are 5mm thick.

Given the shape of the seals, either 82mm or 84mm on the /7 should seal just fine. Not sure why the /6 cylinder measure longer when all Airhead engines have the same stroke.

We never cared about any measurement. We just gave the ring a tap if we saw any sign of leakage. Then a tap or two would show if the ring bounces back, or stays put. We judged the position by looking at the rubber get compressed. From experience, we knew what it would take to seal up. If it bounced back, then the rubber was too old and needed to be replaced.

As I remember, we would find differences in the rubber, maybe revealing a different supplier. At this late date I can't imagine that there is only one rubber donut and they all act the same. Judge by the look and feel.