Hello, I am new to the club and purchased my first airhead (1972 R75/5 "Toaster") less than a year ago. I have refreshed it - carb rebuilds, fork oil / boots, electronic ignition, fluids, cables, ... It is running great now. I know the pushrod seals will need to be replaced sooner than later; it had very minor leaks. I used a Cycleworks seal drift tool and slightly moved the collars enough to stop it completely. I did notice however that one of the collars actually "spins" on the tube but does not leak now. My question is should I attempt to replace ALL the pushrod tubes now with new stainless ones or try to find a oem one that I will still have the ability to move the collars if needed? Relacing one is easier than all 4! I have not done this before but think I could do it. Any suggestions would be of great help!
Welcome to the Airhead community !
These push rod tubes (PRT) come out through the bottom of the cylinder, while the cylinder is off the bike. So the best time to do this repair or replacement is when the PRT Seals are themselves being replaced. Airhead PRT Seals harden with age with the help of being soaked in engine oil and subjected to high temperatures. They generally need replacing every 10 years (seemingly regardless of mileage). If you are doing other work on Airhead heads or cylinders, then it is highly advised to do the rings, gaskets AND PRT Seals at the same time. One is not generally done without the other 2.
Other knowledge you may/may not be aware of....
> Any oil that leaks from the tube will be oil that is supplied to the rockers, and which is draining (by gravity) back into the sump. So that oil is not under oil pressure. (The internal space may be under some slight air pressure, as all reciprocating engine sumps are.)
> In the 1970/80's if owners complained of leakage at the PRT Seal it was common practice to drive the PRTs themselves a little deeper into the seal rather than go through the time and expense of a top end tear-down. In 2025 this means that any PRT may be abnormally low or out of position. It is therefore "best practice" to measure each tube to make sure they are equally extended from the cylinder while the cylinder is "on the bench".
> PRTs are a "light force fit" into the cylinder. This means that if any tube is loose enough to spin, then: 1. the tube could be under-size, 2. the hole in the cylinder could be over-size, or 3. both parts could be out of spec. Some measurements will needed to understand the root cause of your issue, and implement a lasting repair. (Which due to the high cost of BMW gaskets is a job best done only once.)
Best of luck with your repair. Let us know how it goes and please ask if you need additional help.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thank you for the reply. To clarify, only the pushrod tube collar is "spinning " not the entire pushrod tube. On the earlier pushrod tubes, like mine, the collars were friction fit and not braised on like later ones. I just wanted to know if using new stainless pushrod tubes with fixed collars would be worth loosing the ability to move to collars to make small adjustments to the seals. Thanks!!
I worked at a BMW dealership back in the 1970's. Most (99%) of the time the tool was used was because the PRT Seals started to leak while a new bike was under warranty. The customer would complain at a regular service and wanted the leak to stop. So the mechanic would adjust the PRT position to apply more pressure to the PRT Seal. This was more of a shortcut than anything. The original seals were still new and supple, so there was no reason to suspect that taking 4 hours to add new seals was going to have any different result.
That's the only time I've ever heard or seen the PRT drift being used. The tool (and thus the ring) was not for everyday use.
You have a different issue. The loose rings have been known to "jingle, jangle, jingle" like the cowboy spurs in the old song. If this was my bike, I would wash that PRT with soap and water... then squirt clear RTV silicone under and around the ring. Then go ride. After 500 miles you may see excess oil consumption, white smoke, low compression, oil leaks, bad PRT Seals... but most probably not. Airheads (unlike Jap and Brit bikes) retain their composure very well during storage and after 40 years.
BUT if you DO see any of those, then you'll have a REAL reason for a top end tear-down. Then you can do the gaskets, rings, PRT Seals, PR Tube swap and whatever else is called for all at the same time.
Not clear which nationality of bikes you may have come from, but in the Airhead world we do not take top ends off "just for inspection". These engines are like no other bike in the world. 250,000 miles before the first engine issue is the norm. You may need to push the reset button on your thought process if you came to Airheads from Japanese or British bike brands.
Welcome to Airheads !
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Richard. Thanks again for your help. I used the prt collar tool on the advice of a BMW mechanic (actually from his retired father!) I realize it is just a temporary fix, however as I said, the leak stopped even with the loose collar! (It must have still seated the seal better) the leak was never that bad. I'm just trying to prepare for the future. Replacing the prt and seals will probably eventually need to be addressed. I have been researching on how to do the job. The only discrepancy I have found is setting the correct prt depth. (Anywhere from even with the flange to 5mm down from it). For now, I'm a believer in if it ain't broke, don't fix it. The bike is running great and I'd hate to do anything unnecessary to change that. Compression on both cylinders is good, not burning oil, smoking, or fouling plugs. Part of the reason I got an airhead is to learn all about repairing it. The engineering and ride can't be found any longer! BTW, the odometer reads 27000 miles. The bike appears to be very original and I believe it is correct. (I think that I made a good buy!)
Thanks again!!
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Being new to Airheads, you may want to research a series of posts I did several years ago. Most of these articles you'll want to know about eventually, but one in particular is something like "Bringing an Airhead out of Long Storage". It has a list of the top issues other users (including myself) have found that storage caused or brought to the forefront.
You can find all these articles using the Search icon in the top RH corner of the screen because all these subject/titles start with the 2 words "Home Mechanic:"
* In second place of most useful is probably the article explaining about the 'under-tank brake master cyl' and how it can screw up the starter relay.
* Also be aware that some printed specifications have changed since the bike was new.
- Tire pressures on modern tires run about 10% higher than the book values.
- High test ethanol fuel is fine as long as you check the valve clearance every 5000 miles and DON'T ever leave it in the carbs during winter parking. (Read up on Top Tier fuels, https://www.toptiergas.com/ )
- It is to your great advantage to use synthetic gear oils in the gear box, drive shaft and final. For engine oil either Mobil-1 15W50 or Valvoline VR-1 20W50 will do nicely in all seasons.
👍
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Richard,
- Thanks again for the info. I actually found those articles online before I purchased the bike (very helpful). I am only using ethanol free fuel and add chevron techron additive every 3000 miles per the directions. "Luckily", the /5 has drum brakes, so no master cylinder or brake lines to worry with. As for winter storage, I live in South Florida, so it's not an issue. I'm lucky enough to ride year round! I'm sure I'll have more questions in the future and appreciate your help. There is a tech day coming up in north Florida next month and hopefully I can attend it to meet fellow airheads!
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