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New Member Howdy, and an R27 with Leaky Pushrod Tube

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nonfiction
Posts: 4
Joined: Sun Jul 17, 2022 9:01 pm

New Member Howdy, and an R27 with Leaky Pushrod Tube

Post by nonfiction »

Howdy there. Longtime listener, first time caller here, Scott in Seattle. Lifelong motorcycle guy, but new in 2022 to BMW ownership, despite digging them from afar for decades.

Last winter I bought a very nice, well loved '66 R27. The bike ran nicely (if, uh, rather languorous under acceleration :lol: ). The biggest issue for me with this thing is that the exhaust pushrod tube is leaking.

I pulled the cylinder to replace the rubber seals, but the leaking got worse. I thought it was a gasket failure because I hadn't replaced the base gasket, so I went back in to replace the base and head gaskets, whereupon I discovered the piston was in rough shape--had evidently been run hard while too cool, and had marks corresponding with the studs "Classic 4-corner seizure" my graybeard buddy called it. Ick.

Pulled the parts, jug to machine shop to measure and bore; piston ordered and handed to machinist; parts returned ready to go, new stack of gaskets, assembled like it. Fired up this morning--YAY I DIDN'T BREAK IT by replacing the piston and rings (my first time being that deep inside an engine), but the leaking is way worse now.

I suspect I have a split or otherwise damaged pushrod tube. Here's a video I shot of this, and I wonder if you can tell me anything I'm missing here, or whether this in fact looks like a leaky/busted pushrod tube. https://youtube.com/shorts/J5Re2PzVJnY?feature=share
Attachments
IMG_1037.jpg

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vechorik1373
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Re: New Member Howdy, and an R27 with Leaky Pushrod Tube

Post by vechorik1373 »

It looks (though it is hard to tell in the video) that the oil is coming from around the push rod tube. Either it is a loose fit in the cylinder, or it is cracked.

If the tube is cracked, your going to have to take it back apart, get the cylinder off, and either buy, or make or have made, (if you know a machinist) a push rod tube drift. This is used to drive the pressed in tube out of the cylinder, and used to install a new tube into the cylinder.
The end of this tool, slides into the push rod tube, and the shoulder above the the turned down area, is just slightly smaller than the hole in the cylinder for the push rod tube. This allows you to drive out the tube, and not get the tool stuck in the cylinder. It is also used to drive the new tube into the cylinder. All you need is a hammer.
pushrod tube2.jpg
Vech
Technical Adviser, Former owner, Bench Mark Works
662 312 2838 cell 9 am to 4pm CST PLEASE!

nonfiction
Posts: 4
Joined: Sun Jul 17, 2022 9:01 pm

Re: New Member Howdy, and an R27 with Leaky Pushrod Tube

Post by nonfiction »

Thanks Vech! I went back and looked again at the video, then into my shop and at the bike. There's oil on the fin above and around to the right from the pushrod tube hole, so I suspect I might have a leak around one of the head studs. Need to pull it back outside and fire it again, and look at the oil leak more critically, seeing it's so visible. I am starting to think I should have had the machinist check the head's and jug's mating surfaces are parallel--rookie mistake. I'll post what I find.

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vechorik1373
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Re: New Member Howdy, and an R27 with Leaky Pushrod Tube

Post by vechorik1373 »

After you put it back together, and ran it, (how far?) did you go back and re torque the head bolts?

After 50 - 100 miles you must re-torque the head bolts.

And, when you had it part, get you take the correct tap, and run it down into the threaded holes for the head bolts in the cylinder?

You see, the head torque of 28 ft/lbs is not really all that tight. And there was rust, dirt whatever in the thread of the cylinder, the torque wrench will lie to you. It will show higher torque, due to the interference of rust and dirt in the threads. With the head off, you should be able to take a head bolt, and screw them into the bottom of the thread with just your fingers. Trash or rust in the threads = resistance.
Vech
Technical Adviser, Former owner, Bench Mark Works
662 312 2838 cell 9 am to 4pm CST PLEASE!

nonfiction
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Joined: Sun Jul 17, 2022 9:01 pm

Re: New Member Howdy, and an R27 with Leaky Pushrod Tube

Post by nonfiction »

I didn't do what Vech said, chasing the head bolt threads with a tap. But they all went in pretty easy (with fingers).

Circling back on this, here is what I found.

I ran it again, rode it around to get it good and warm. It was of course drooling. I parked it in the light (and on the centerstand this time, so the oil will go show up where it originates instead of running around the base of the cylinder and puddling up on pushrod deck).

Watched it some more, and it seemed to be coming out the head gasket, from area around right-side forward stud.

Pulled the head back off and noted wet oil on top of the piston, and signs on the gasket of oil sneaking by the topend oiling port 'smile'.

Note belt/suspenders approach with silicone gasket, coated with copper spray, and thin high temp RTV skim on metal surfaces. Am I trying too hard here? I did observe a few little tendrils of extra RTV in the oiling area there on disassembly; it went back together with considerably less sealant than the initial assembly, to avoid that.)
68091107765__CC56C312-381F-46AB-B4D9-C5988E170240.JPG
Seems my suspicion was right; the head is warped. I put it on a plate of glass and rocked it, and noted about .006 feeler could get under the edges. https://youtu.be/0qU4zlx6nFs

Glued some wet/dry 600 grit sandpaper to the glass, hosed it down with WD40, and gave it a few tentative slides on there. I've never done this before, so I felt like a big boy. Inspection after the first quick pass showed what I thought:
IMG_2355.jpg
So I hit it some more, until there were no more low spots and it all looked of a piece.
IMG_2360.jpg
It's all back together now, and there are still a few drops of weep after a ride, I think from the base gaskets. I can live with that; matches the carb in that regard. Took it for a couple rides across town and back, ~12miles each, <35mph.

I will torque the head bolts again, and maybe that'll subside anyway. Thanks for the help here! (and sorry about the weird upside-down picture!)

nonfiction
Posts: 4
Joined: Sun Jul 17, 2022 9:01 pm

Re: New Member Howdy, and an R27 with Leaky Pushrod Tube

Post by nonfiction »

Spent a day giving the surfaces some luv:
IMG_2413.JPG

Daves79x
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Re: New Member Howdy, and an R27 with Leaky Pushrod Tube

Post by Daves79x »

Congrats - seems like you are getting there. Do you buy head gaskets in bulk? For the base gasket, it needs coated with Ultra-Gray as well.

Dave
Dave

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