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Siebenrock Power Kit for my 1971 R75/5 - Cylinder base sealing

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Clark Morris
Posts: 9
Active Member
Topic starter

I bought a Seibenrock Power Kit for my 1971 R75/5. 

The original 750cc cylinder bases are FLAT and use a metal gasket with Dri Bond to seal the cylinder base.

The Siebenrock 1000 CC power upgrade kit uses small black o rings (with the milled grooves in the cylinder base) and a large white o ring (again with a milled shallow groove) on the cylinder base.  The Siebenrock kit did not come with the metal base gasket, and the instructions did not call out for using Dri Bond base sealant.... So I installed them without the metal base gasket, and did not use Dri Bond sealant, because I thought I heard that later models of Airheads did not require anything other than the o rings.

Upon doing the oil pressure test after cylinder installation, oil came out of the rockers as I expected, but also starting coming out around the cylinder base....

I am now ordering new metal base gaskets, and Dri Bond to install like the original cylinders were done.... My question is "Should I use the large white ring (as well as the small black ones) in addition to the metal base gasket and Dri Bond sealant?


I noticed the Mr. Brookes did a video on installing a new Siebenrock kit on an R80.... He used the black O rings, metal gasket and Dri Bond...... I am concerned about using the big white Oring in addition.... There is a shallow groove for it, but I don't want it to interfere with the metal base gasket... This gasket will sit at the crankcase and the orings will sit in their grooves on the cylinder side, with the o rings sitting against the metal gasket.

This will be my third time around doing these cylinders.... The originals turned out to be a bit too leaky compression wise... so I broke down and bought the upgrade kit to make it worth my while working on this bike.... I don't want to do it wrong one more time!  I want to ride this dang thing.... I have been restoring it for more than a few years now and getting tired waiting....


Clark of the South

ABC #4099

Posted : 12/26/2023 15:21
David Elkow
Posts: 289
Reputable Member

I hope you found an answer to your question. When I read your description of the situation, even though I do not know the answer, I did have a concern. That being - the small o-rings seal oil pressure supplied to the rocker arms. If the metal gasket is used, will the small o-rings be properly compressed and seal to oil flow to the rockers?  I’ve never worked on a bike with the metal gaskets at the cylinder bases. My ‘78 has no base gasket or large white o-ring - just metal to metal with sealant. I DO have the small o-rings that fit in the recesses around the top stud holes to seal the oil pressure to the rocker arms.  

Posted : 01/03/2024 19:21
David Elkow
Posts: 289
Reputable Member

P.S. -  Very nice looking /5!  And, what are those two electronic? devices (dark grey boxes with green dials) on the counter behind the bike?  

Posted : 01/03/2024 19:30
David Elkow
Posts: 289
Reputable Member

I apologize. I re-read your post and realized that when you cranked the engine to test oil flow to the rockers, the same oil also flowed out at the cylinder bases. So, the small o-rings were not sealing the oil passage. I get it. 

Again, I hope you already have your answer and all is well. I would guess that you do not need the big white o-ring, and you DO need the sealant.

Just an aside, my last time assembling I used (recommended by Ted Porter and others) Permatex Ultra-Gray silicone sealant. I liked it because it claims “tack-free” in one hour. The Dri-Bond says tack-free in 10-15 minutes. I enjoyed the longer working time.  Didn’t feel under a time crunch to get things together. I let it cure 24hrs before starting the bike. It seems to have done an outstanding job!  

Posted : 01/04/2024 06:10


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