Saturday, November 17, 2018

Tech Day: Top End Removal for a BMW Airhead

This past saturday, the 10th of November, I rode over to Brook R's home in Arvada, Colorado to watch him and Dick P, the Colorado Air Marshall work on Dick's 1972 R75/5 Airhead.

One of the four rods which hold the left side cylinder/head had become stripped you see, and they were going to show whomever attended the tech day how to repair that.

It was only myself and a young fellow by the name of Jason that showed up to be elucidated.  I'd seen Brook do this once before but it never hurts to see such things more than once!

 Brook is describing the oil passage flow into the head
from within the engine.

Dick had rented a special jig from Northwoods Airheads in Golden, CO to do the repair.  It ensured that when he drilled and tapped the hole for the helicoil insert, that the drill bit and tap tool would be straight and "square".

 Installing the round portion of the jig, which allows it to be
centered on the cylinder's hole in the engine case.
It also supports the connecting rod once installed.

 A shot of the main part of the jig, to show how it
slides along the remaining three cylinder rods.
Dick had already removed the stripped rod, as you can see above.

 Jig in place, tube sleeves are mounted and tightened to
hold the jig firmly against the engine case.

 Drilling out the worn threads.

 Tapping in the new threads prior to inserting the helicoil
which will form the new threads for the rod.

 The helicoil just before insertion, Dick had coated it
with Red Loctite to ensure it stayed in place in the long run.

It was at this point that things went slightly askew.  The helicoil was inserted a little bit too deep and while Dick tried to back it off, the helicoil somehow jumped a thread and got stuck.

 The red stuff is in the loctite, you can see (hopefully)
that the helicoil is in too deep.

Much head scratching ensued.  Several attempts were made to try and get the helicoil bit that had jumped a thread to lift and lie correctly but no go.

The session ended with a stop as it was getting a bit late in the afternoon, while Dick and Brook sent off queries to the jig manufacturer describing the problem and seeing if there were any suggestions/solutions.

I rode back home and got to the usual sunset watching spot with Brigitta but the light was to show better further south due to clouds as Sunset approached.

I rode Brigitta instead to the church parking lot near the house and got these shots instead:

 Pikes Peak, America's Mountain

I checked with Brook and Dick on Monday and they'd solved the issued with the liberal use of Acetone to melt the Red Loctite and a jeweler's screwdriver that he successfully fit under the 1st thread so it could be bent. Then a pair of needle nose pliers were used to grasp the bent thread, and turned counter clockwise to eventually unwind the helicoil insert from the hole.

Brook went ahead and successfully installed a different helicoil into Dick's motorcycle engine and now all is well.  The loctite is curing and will be ready for this coming weekend when they'll reinstall the cylinder and new heads which Dick had procured.  Not sure I'll be be able to attend though, still, I'm glad the issue with the helicoil was fixed and it sure was a learning experience for me.


RichardM said...

Nice write-up with pictures. I remember watching a video of Chris Harris redoing the repair and he recommended using green Loctite for this repair. But, he was using a Timesert and not a Helicoil. The last time I installed a Helicoil was to repair a pulled valve cover bolt on the BMW. After the heads went to the Beemershop for repair, it no longer had the Helicoil installed but repaired by welding and redrilling and tapping the hole. The Helicoil repair worked great and, BTW, I also used red Loctite as I had never even heard of green.

redlegsrides said...

Thanks RichardM, they guys made it look easy and also showed "grace under pressure" when encountering the helicoil being in too deep issue.

I believe I'd be able to do the operation on my own, though apparently, my year R80 engine comes with an additional O-Ring that can be messed up easy if one isn't careful, so no rush on doing a top end rebuild.

Steve Williams said...

Each time I look at one of these mechanically instructive, DIY, engineering rich posts I hope the fix-it flame within me flickers to life once again. I used to love these sorts of mechanical challenges years ago when I lived beneath old cars. But now, no matter how much I try to convince myself, the fire is gone. I don't even like checking air pressure now.

It's a fine post and a benefit to anyone with an old airhead who encounters such a problem. Thank god you thought to include a sunset for those weak readers who live on more abstract diets.

I was in the garage today and was bemoaning my decision to purchase a Harbor Freight motorcycle lift table. It's huge. Works well but I've never used it. I suspect sometime soon I'll be listing it on Craigslist.

redlegsrides said...

It’s ok Steve, as you read and some recent personal experiences of my own show that sometimes doing the right thing can lead to other problems. Some days I really shouldn’t be allowed near tools.

If I lived closer to you I’d come get that moto lift table....I’ve wanted one but storage would be an issue I’ve not solved.

RichardM said...

The motorcycle lift can be stored under Martha's car.

redlegsrides said...

Last time I looked was when she had the BMW and it had perhaps 1/2 clearance depending on how she pulled into garage....the lift is apparently 6.5 inches tall when folded....I think the Honda CRV has less clearance....not to mention also moving 300 lbs around!

redlegsrides said...

1/2” that is....

Unknown said...

This how-to article is perfectly relevant to the pulled cylinder stud I discovered today while trying to adjust rocker shaft end float and adjust the valves on my 1985 BMW R100.
I have made a similar jig for similar repairs for an airplane engine.
Where did you buy the thread repair insert?


redlegsrides said...

Thanks Unknown...the helicoil inserts came with the jig that Dick rented.

RichardM said...

Helicoil inserts are available at any really good hardware store. Around here, AIH (Alaska Industrial Hardware).