Your favorite pushrod tube seal replacement link

[ebeeby]

Well, time to do the pushrod tube seals again. It's been 11 years. I searched the forum and was overwhelmed with all the link choices on this topic.
Please post your favorite link.
Last time I did this was to pull the heads to send to Ted Porter for valve recession. I used Oak's Top End manual.

 

[20774]

There are a couple of past threads in the Similar Threads pane at the bottom of the screen.

There are a couple of youtube videos on pushrod tubes in this link:

https://forums.bmwmoa.org/showthread.php?75891-On-line-Maintenance-Videos

Although they aren't videos, there are a couple of other references to pushrods in this link:

https://forums.bmwmoa.org/showthread.php?47142-Resources-and-Links

 

[brook.reams]

Well, time to do the pushrod tube seals again. It's been 11 years. I searched the forum and was overwhelmed with all the link choices on this topic.
Please post your favorite link.
Last time I did this was to pull the heads to send to Ted Porter for valve recession. I used Oak's Top End manual.

Hi ebeeby,

You didn't mention the year/model of your bike, and there are some minor differences based on which valve assembly you have. Here are links to documents about doing this work from my web site for a /5 and an early RS (essentially a /7 valve assembly).

1973 R75/5: https://brook.reams.me/bmw-motorcycle-rebuilds/1973-bmw-r755-rebuild-project/11-bmw-r755-install-engine-top-end/
1977 RS: https://brook.reams.me/bmw-motorcycle-rebuilds/1977-bmw-r100rs-rebuild-project-index/11-bmw-1977-r100rs-install-connecting-rods-and-assemble-top-end/

They contain a list of references from experts including Snowbum and Oak.

I hope these help.

Best.
Brook Reams.

 

[robsryder]

Perhaps the most expensive part of doing the push rod seal replacement is the cost of a new head gasket. With my 93 R100GS/PD I found that I could keep from replacing the head gasket by not separating the head from the cylinder. Thus, I left the 6 and 12 o'clock nuts pretty tight (perhaps slacked off by 1/4 turn to reduce tension but not allow head-cylinder movement). The other 4 head nuts were removed along with the rocker assemblies (maintain orientation of parts). Remove push rods then gently move cylinder-head away from engine case until piston skirt is visible. When wrist pin is visible remove snap-ring (much easier with "newer" airheads). Push out wrist pin, keep piston in cylinder. Don't let con rod fall onto engine case; a rag beneath con rod helps.

Renew push rod seals and o-rings at top studs. I clean engine case and cylinder lower surfaces and renew adhesive (very light coating, be careful no to block passage along top studs). I use to use Hylomar, but have begun using Honda Bond or other similar 3Bond adhesive product.

It can be helpful to place a jack beneath the engine to slightly elevate to help new push rod seals clear frame. Or one can rotate push rod seals 90 degrees to clear frame - make certain to rotate back before seating seals into engine case. A light coating of oil or silicone on outer push rod seal surface can help with seating in engine case.

Area about engine case, cylinder, and push rods should be thoroughly cleaned before disassembly.

When cylinder is removed from engine, it is a good opportunity to remove and examine cam followers. Some strongly recommend against using magnets to extract the cam followers as the magnet might slightly magnetize the followers and result in attraction of metallic fines henceforth. A small suction cup might be used to extract the cam follower.

Don't forget to reinstall wrist pin and circlip when re-installing cylinder-head.

I have seen the push rod seals replaced in the aforementioned manner at airhead tech sessions. It took about 2 hours to do both sides.

 

[brook.reams]

Perhaps the most expensive part of doing the push rod seal replacement is the cost of a new head gasket. With my 93 R100GS/PD I found that I could keep from replacing the head gasket by not separating the head from the cylinder. Thus, I left the 6 and 12 o'clock nuts pretty tight (perhaps slacked off by 1/4 turn to reduce tension but not allow head-cylinder movement). The other 4 head nuts were removed along with the rocker assemblies (maintain orientation of parts). Remove push rods then gently move cylinder-head away from engine case until piston skirt is visible. When wrist pin is visible remove snap-ring (much easier with "newer" airheads). Push out wrist pin, keep piston in cylinder. Don't let con rod fall onto engine case; a rag beneath con rod helps.

Renew push rod seals and o-rings at top studs. I clean engine case and cylinder lower surfaces and renew adhesive (very light coating, be careful no to block passage along top studs). I use to use Hylomar, but have begun using Honda Bond or other similar 3Bond adhesive product.

It can be helpful to place a jack beneath the engine to slightly elevate to help new push rod seals clear frame. Or one can rotate push rod seals 90 degrees to clear frame - make certain to rotate back before seating seals into engine case. A light coating of oil or silicone on outer push rod seal surface can help with seating in engine case.

Area about engine case, cylinder, and push rods should be thoroughly cleaned before disassembly.

When cylinder is removed from engine, it is a good opportunity to remove and examine cam followers. Some strongly recommend against using magnets to extract the cam followers as the magnet might slightly magnetize the followers and result in attraction of metallic fines henceforth. A small suction cup might be used to extract the cam follower.

Don't forget to reinstall wrist pin and circlip when re-installing cylinder-head.

I have seen the push rod seals replaced in the aforementioned manner at airhead tech sessions. It took about 2 hours to do both sides.

Hi Robsryder,

I'm a bit uncomfortable about suggesting someone keep the head gasket because it costs too much (it's $17 plus change per gasket). It seems to me that's not expensive compared to the fun of a blown head gasket and potential warping of the head when it's secured with only two nuts.

The head gasket metal ring crushes when the head bolts are tightened which reduces their ability to seal after you reduce the pressure and then reapply the pressure. So in my view, the gaskets are "use once". I always replace them when doing push rod tube seals.

When adjusting valves, we do slacken two of nuts securing the heads, but never all four. I guess I feel like four nuts keep sufficient pressure on the head gasket to not risk it blowing at some inopportune time and place.

Anyway, each to their own when if comes to risk vs. cost of parts.

Best.
Brook Reams.

 

[robsryder]

I use to always replace the head gasket, but as an experiment decided to try with doing so using the method I discussed above. For me, this worked well, no head gasket leaks and no blown gasket. The head / cylinder face was never disturbed and the crushed metal gasket was unperturbed. Since then, I've seen several other push rod seals replaced without renewing the head gasket.

If there is any disturbance of the head / cylinder, then I definitely think that replacement is desirable. And if it has been a while since the piston crowns and heads have been de-carboned, then one may wish to remove the head anyway. It does really depend on one's needs, circumstances, and comfort level. Personally, I always have a set of head gaskets, push rod seals, small stud o-rings, and 3bond sealant on hand "just-in-case".

 

[ebeeby]

Thanks all for the replies. Just to confirm my signature: 1973 R75/5 LWB

Also to confirm, the 1973 R75/5 LWB does NOT have the small o-rings - correct?

 

[20774]

Also to confirm, the 1973 R75/5 LWB does NOT have the small o-rings - correct?

If you believe RealOEM, it does not have the small O-rings...when I enter the info for my /7, it shows that my bike needs to the O-rings. Also, according to RealOEM, it doesn't show anything between the cylinder the engine block. That doesn't seem right to me. I think the early /5s had at least some kind of metal gasket material. Of course you could see what's in there when you take it apart. Or you could order parts from someone like Tom Cutter and know that he'd send you the right parts.

 

[robsryder]

The parts fiche at MaxBMW does not show the small o-ring (that goes about the top two studs). Image 11-1727

https://shop.maxbmw.com/fiche/DiagramsMain.aspx?vid=51885&rnd=07242017

 

[20774]

The parts fiche at MaxBMW does not show the small o-ring (that goes about the top two studs). Image 11-1727

Actually you want image 11-1728. Note in the parts list that item #7 isn't shown...none of the parts other than the tube of DreiBond.

Side note...I hate the way Max doesn't let you hot link directly to the figure...at least I haven't figure it out yet!

RealOEM has this link...but indicates "no parts are found".

https://www.realoem.com/bmw/enUS/showparts?id=0260-EUR-05-1973-2476-BMW-R75_5&diagId=11_1728

 

[robsryder]

I saw the image 11-1728 showing the o-ring, but since no part was shown in the list, only the 3-bond, I didn't think that the o-ring applied. Frankly, I don't recall if an o-ring was used on my R75/5. I know that I used one on my 75 R60/6. I was quite interested to learn that the 74 R60/6 did not use an o-ring.

If the lower part of the cylinder base has a machined out area about the top stud hole, then I would be inclined to think that an o-ring is intended to be used. If there is no place for the o-ring, then I would not use one. One should still take care to avoid getting the 3-bond sealant in the top stud holes. As I recall
I place a very light coating of 3-bond on the engine case, both sides of the aluminum base "gasket or shim", and the cylinder base. The operative word is "light" coat of sealant.

Just for reference, here is the image 11-1728 from the MaxBMW parts fiche. Item #7 is the o-ring about which we have been discussing.

 

[20774]

Snowbum has some info in the middle of this page:

https://bmwmotorcycletech.info/cylinders.htm

He states:

In late 1975, BMW lengthened the cylinders by 0.5 mm, and eliminated the gasket, & increased the spigot from 97 mm to 99 mm in diameter. The cylinder top studs area used O-rings, the cases being machined for them. No standard cylinder base gasket/shim was used!

I didn't really know this, but it seems that there's a physical difference in the early cylinders which didn't allow room for the small O-rings but instead used the base gasket. After that, the gasket was eliminated and the two O-rings showed up. When he says late 1975, I believe he's talking about the calendar and that would mean that he's referring to the 1976 models.

 

[brook.reams]

Thanks all for the replies. Just to confirm my signature: 1973 R75/5 LWB

Also to confirm, the 1973 R75/5 LWB does NOT have the small o-rings - correct?

That is correct, there are no o-rings on a 1973 engine. Earlier in this thread, I added a link showing how to do this work which includes a parts list. There are no O-rings in that parts list.

It is common practice to draw a fiche diagram with several versions of an assembly. If the part # in the fiche is not shown in the list of parts for a particular model/year, it means it is not used.

I hope that helps.

Best.
Brook Reams.