Doing push rod tube seals-need advice

[Workinman]

Okay… I’ll try to answer some of your questions and concerns.
First off, there ain’t no way this bike has 129,000 miles on it. A bike with that mileage shows obvious signs, and this bike has none of them. I DO wonder why the engine has been apart with only 29,000 on it, but I’ll probably never know the answer to that. I’m hoping that it was to do the head work for the unleaded fuel. This bike sat for 20-25 years before I bought it. Keep in mind that the only reason this motor was torn down at this point was because the PRT seals were pretty dried out and seeping. It runs perfectly, starts fine, idles fine, no smoke of any kind, and no noises of any kind. I did not know the PO at all before I looked at his bike, which I found out was finally for sale by one of his daughters. He didn’t remember where any of the paperwork was. I did, just recently, get a box that they found in the garage with the original mirrors, the battery covers, a couple of service manuals, and a brand new front brake rotor from BMW. Not sure why he bought a new rotor and socked it away but I’m guessing it’s worth a few bucks as the only ones I see are aftermarket.

As for the extra base gaskets, that just doesn’t make much sense to me. I know a thing or two about engines, as my car I just recently sold had a built 440 in it with custom head gaskets to lower the compression. But those gaskets were .090 thick if I remember correctly. And I still had around 11.5:1 compression. Adding one of these EXTREMELY thin base gaskets wouldn’t lower the compression enough to make any difference. I haven’t measured the thickness of the gaskets yet, but I will later and report back. When I head out to the garage today I plan to measure cylinders, pistons, rings, gasket thicknesses, etc. At that point I will come up with a plan. I will probably just give it a light hone and maybe throw some new rings in it since I have it apart. The piston skirts show no signs of blow by or scuffing whatsoever. Measuring everything will tell me more.
I do think I’m going to redo the black on the cylinders. I can’t bring myself to putting it back together like that. I’ve done the paint thing, the powder coating thing, and the ceramic coating thing, so I just need to figure out which route I’m gonna take here. My guess is that with the miles this bike will get ridden a good paint job will probably be just fine.
I’m also not sure about the sealant on the base gaskets. Does BMW really want a sealant used here? I’ve never used any kind of sealant on any base gasket before. Granted, most of the motorcycle engines I work on are Japanese, and a few Harleys sprinkled in for flavor, but I’ve never used a sealant on the base gaskets. With that being said, the sealant I normally use elsewhere is the Ultra Black or The Right Stuff. Will that work here, do you think, or should I find some grey stuff? And while we’re at it, should I put some sealant around the base of the push rod tube seals where they meet the block?

So that’s where we are right now, fellas. I’m gonna go out in a little while and clean, measure, and inspect the parts, so I may know more then. I’ll check back later for follow ups and such.

Thank you.
I’ve thrown in a picture of a couple of my last restorations.

[Workinman]

I forgot to mention that I did a compression test before I ever rode the bike and I got 135 both cylinders. I guess it’s possible that number has changed a little since I’ve wakened it from all its years of slumber.

[schrader7032]

You're going to want to use the proper base gasket sealant on these engines. The BMW twin is unique in that with the way the pistons rotate, each explosion in the combustion chamber is trying to blow the engine top end off the block. That's a relatively good amount of movement so a flexible yet good sealant is needed for preventing oil seepage. Snowbum talks about sealants in the bottom half of this page:

https://bmwmotorcycletech.info/cylinders.htm

As for the base gasket, I did a top end on my /7 and used a Siebenrock aftermarket kit. The kit resulted in a step up to 9.5:1 compression ratio which was more than the original ratio which was around 9.0:1. I didn't want to have to consider using tricky timing gimmicks to keep the engine from pinging over time. So, I opted for an R60/6 part 11 11 1 335 650 which is 0.67mm thick. I was told that it lowered the compression ratio to just under 9.0:1 and I thought that made sense. I'm happy with the results and not having to worry about gasoline issues.

Stock, the R90S was 9.5:1. Likely it doesn't need the reducing base gasket. The R60/6 was a pinging machine because of the camshaft design...it was so close on timing that it needed some help. It was 9.2:1 but again the camshaft profile made things worse.

[srankin]

Thanks for the added details. So far you have things in hand. Honestly, I had a bike with the same compression ratio and never had an issue with pinging as long as timing stayed put. My current 84 R80RT was rebuilt years ago with higher compression pistons bringing it up to 9.5 and it runs fine. So I wonder why there are two base gaskets?

Take a look at Snowbum's website and see if he makes any mention as to gaskets.

To be funny, you would be surprised at some of the over 100K bikes I have seen that don't show that kind of miles. Then again, I have seen 30K bikes that looked like they were in the war. It depends upon the care of the bike. LOL, I have over 200K on my R80RT and it looks pretty much brand new with the exception of minor things missing and a different color paint than factory new.

I have always painted my cylinders on all of my bikes black using hight temperature dupli color paint, it lasts a long time and is a lot cheaper than powder coat.

You have a very nice looking bike and I am jealous, I can't find bikes that have been off the road that long in that condition. Most of what I find look pretty bad. St.

[Workinman]

Hey guys! I’ve been busy wrapping up a couple of other projects lately so the R90 got put on the back burner. I’m back to working on it now, so I’ll be running some more stuff by you. Again, thanks for your help.
First, after doing some research, and reading Snowbums stuff, I’ve decided to leave the cylinders alone as far as honing. The cylinders look good, even though the cross hatch is not as pronounced as I would like it, and the compression was good, it didn’t smoke at all, no piston slap or any of that. I’ve bead blasted the cylinders and primed and painted with high heat low gloss rattle cans. They look good now, and I will give them several days to cure before I start messing with them again. I’ve removed the push rod tubes and cleaned them up, and I’m doing research on how to properly reinstall them. Any guidance you can offer here would be helpful. I’ve read the the flange on the tubes should be level with the mating surface on the cylinder, and I’ve read that it should be 2-3mm off from level. I did take some rough measurements before I knocked them out, so worst case I’ll just put them back where they were. You never know if someone had tried sealing them up in the past by tapping them in towards the block with that special tool that I’ve seen. There was one of those tools in the box of parts I received recently from the PO’s family, so I have to assume it’s been used. Also, I’ve read of a green sealer that maybe should be put around the tubes where they go into the cylinders. Is this something I should do? I didn’t notice any kind of sealer when I popped them out.
Next, the base of my studs was pretty nasty looking. I’m gonna clean all of that up, of course, but I’m wondering if that’s normal. I’ll try to toss a couple of pictures in when I’m done. I’ve also gotten a second set of base gaskets, all 4 of which match the thickness of the ones that came off, so I won’t be changing anything there.
My gasket kit came with 8 o-rings that go under the rocker bosses, if I’m not mistaken, but mine didn’t have these on there. The manual says “If used” or something to that effect, so I’m just assuming that they weren’t used on my engine.
Also, the rubber collars that seal the intake elbows to the air box and to the carb. Are all 4 of those the same size? I’ve seen some collars listed as carb to head collars, but that’s not where these go. I need to do more research before I order these, but I figured you guys would know and I could save myself some time. I’m gonna go back and reread Snowbums stuff, but I don’t remember him mentioning these.

I believe those are all of my questions for now, but I’m sure I’ll have more as I start reassembly.
Thanks again for your help!
Chris

[schrader7032]

As for the pushrod tubes, put a flat edge across the base of the cylinder. The straight edge should just touch the ring on the pushrod tube.

[Workinman]

Thanks, Kurt. That seems to be the most popular way. Unfortunately I didn’t measure that end, I measured the top and the distance from the top. Your way is probably much more accurate.
Any sealer on the top where they go into the cylinders? Possibly green? I don’t think I’ve ever SEEN a green sealer.

[schrader7032]

Usually a non-hardening sealer is used like Permatex Ultra Gray, Yamabond, or Hylomar. Be careful to not get sealant around the oil outlets on the top bolts. Snowbum covers all this.

[Blythe59]

Hi, Nice machine you have there.

Re the oil pan, personally I would go for it, I've had two 90s's and changed the sump pan on both, the advice from my dealer at the time, and currently, is to use the spacer on the oil pick up and keep the original dip stick maintaining the oil level as original.
I covered quite some milage around europe from the UK on both these bikes, usually at a high cruising speed and never had an issue, the additional oil and larger frontal surface area on the sump kept things normal.

Incidently if you are changing the pushrod tubes for either steel or stainless steel make yourself a drift which is a nice sug fir, and if you can, use a press to install, it's not a difficult task, this just makes it smoother with little room for error, Oh and by the by, make sure you align the mark on the seal in the correct location using a SMALL amount of silicone lube on the seal as you install. If the bike has been stood for any length of time it's worth schecking for oil on top of the gearbox casting, if it;s wet you'll need to replace the rear crankshaft seal, they harden with age and take a "set".
Then go ride, have fun, the 90S is a terrific bike to ride and eats up the miles on a long journey in comfort, from memory I think the longest single journey I made was from my home in East Yorkshire in the north of the UK to Dijon Prenois for the coupe moto legende, pouring with rain all the way for the last five hours and the bike never missed a beat. 720 miles and I got second place in BMW's ninetieth birthday concourse, very happy:)

[Bluethumb]

In looking for someone to do any work on the heads have you thought to contact Boxer2Valve? They’re in Hendersonville and should have a shop that does their work since they specialize in Boxer 2 valve bikes.