Exhaust valves went tight

[ebeeby]

Long trip to Colorado. About 2000 miles. By the time I got to Colorado (900 miles) the bike (73 R75/5) became very hard to start. I thought it was just the altitude.

Back in Dallas however still hard to start. Acted like it was running out of gas. Decided to check valve lash and both exhaust valves were tight. Adjusted and the problem is solved (for now). Engine starts very easily and runs great. Tight exhaust valves reduced compression sufficiently not to draw fuel from the carbs , especially at idle. Both intake valves were a very little loose.

Question for the longtimers: Could it be that the long hot 600 mile first day through Texas de-carboned the heads sufficiently to tighten the valves? The 1973 R75/5 is not known for valve recession is it? Is this wishful thinking on my part?

[20774]

You say tight...any clearance all? And just to be sure, you checked each side at TDC on the compression stroke? I've set intake valves with exhaust clearances, and vice versa...stuff happens!!

All pre '81 motors will eventually succumb to valve recession. It's just a question of time and how hard the motors are run. Heat's the bike issue...the more the heat, the faster the problem. Typically it's the bigger motors... Were you pushing the bike harder than normal? Did you make any changes to the carbs for the trip? If you had things set up for Dallas, going up in altitude would have made things richer, which tends to cool the engine down some.

I'd just set 'em and check again in about 500 miles and go from there...

[PHMarvin]

Hi, Ebeebe,
No, the R75/5 is not known for valve recession (call it what you want) like the '81-'84 bikes. However, the pre-'81 bikes were designed for LEADED premium, which hasn't been available in the USA for many years. Your bike may be telling you it's time to change the valve seats to those designed for unleaded fuel. Or you may have no further problems after adjusting your valves.

I am in the Anonymous book in El Paso, TX. Over 10 years ago I loaded up my bike trailer, my tools and a few parts, and drove the 115 miles to Van Horn in response to a call for help. A young man had an R75/5 which (he reported) wouldn't start and, when he got it to the motel the previous evening, it wouldn't idle and when it was running, it would not go over about 4k rpm. One diaphragm was torn (I had spares) and the exhaust valves were both closed. After replacing the diaphragm and adjusting the valves, the bike started and ran as it should. So yours isn't the first one whose exhaust valves have closed up while being run a long distance, reasonably fast, in a hot climate. BTW, I have no idea what became of the young man or if the valves maintained their adjustment. I did show him how to adjust the valves, though.

[easter85]

How many miles on your bike? My valves on my 1978 starting loosing their adjustment at about 40,000 miles. I had new valve seats, guides, and hardened valves installed by Perry Bushong at BMW of Ft. Worth. I now have 75,000 miles, and other than I wrecked my bike and it is in a pile in a garage, the motor is fine!

[20774]

No, the R75/5 is not known for valve recession (call it what you want) like the '81-'84 bikes.

The '81-'84 bikes did not have valve recession problems; they had heat transfer problems which resulted in valve face plastic deformation. Because the heat couldn't transfer as efficiently through the valve seats into the heads, the valves themselves got too hot and deformed. Prior to 1981, as you mentioned, the bikes were designed for use with leaded gas which helped to lubricated the contact area between the valve and the seat. Without the lead and with abuse, it would seem to me that any pre '81 bike will eventually have valve seat problems. Some sooner than later...

[ebeeby]

I have around 42,000 miles. I'm inclined to the "they tightened up after a long hot day" theory. I'll check them again in 1000 miles of city driving or if the idling/starting problem returns. For now, runs like a champ.

I got stranded in Childress (250 miles short of home) by what turned out to be a shorted Westco battery. I was convinced it was the ignition switch as I had nearly 12 volts on the VOM ( my load tester later revealed the short fault).
In any event, I may not have got it re-started anyway if I had put a battery in it as the tight exhaust valves gave insuffcient compression to start or idel well.

A new Odyssey PC680 and the valve adjustment have restored my faith in the old girl. And the ignition switch replacement didn't hurt me a bit.

Wich I had thought of calling someone in El Paso to come get me .... :)

Eric

[PHMarvin]

[QUOTE=20774;232745]The '81-'84 bikes did not have valve recession problems; they had heat transfer problems which resulted in valve face plastic deformation. QUOTE]


Hi, Kurt,
That's why I said on my post, "CALL IT WHAT YOU WANT." I have heard it commonly called "valve recession" and have heard Oak Okleshen call it "VFPD". Either way, when it is apparent, you need to change the valve seats, valves (ok, maybe the intakes will be ok, but probably not) and maybe also valve guides.

[20774]

Phil -

Oak has certainly written extensively on the subject. He tried to make the distinction between the two different situations...same general problem, but caused in slightly different ways. If this sort of thing starts to happen on a machine, it's really only a matter of time. And, if it's my heads, I'd make the swap all the way around so I was basically starting with a zero-time head...I'm approaching that point...I'm wondering if I'll even change the valve springs, too...

[clone432]

I recently took a 3 day 1000 mile plus ride in mide heat, though with elevation in Washington State.

I had issues idling and starting. I was out with my dad and a couple of his friends. We spent 2 days debating the issue (as I was the only BMW owner), it was argued that the cause was points, plugs,etc. I argued that it could be the valves, though could not back it up with experience.

Any way once I got home I adjusted the valves and found a exaust vavle closed on the left cylinder and a intake on the other.

The correct adjustment cleared any running issues. I plan to re-check the clearances in a couple hundred miles to see if it was an issue with MY last adjustment.

[Polarbear]

My '78 R100/7 still has the original valves all around, at over 300000 now. I bought it new, so all these are my miles. I know the engine will get some new valves,etc soon, because I cannot imagine going too much further, but it still runs like clockwork and has no sign of failure as yet. You don't need to tell me I'm running on a short string here, as I can imagine this myself. I am proud of the old bike, however and it has proven itself so far beyond anybody's expectations,imo.. Its ridden nearly everyday still and most recently(last year) did a 10000 mile loop from CA to Nova Scotia and Vermont last year to the National Rally, where I had ridden this same bike in 1978 to the Vermont National Rally in Rutland. We've been around, I'd say. Anyhow, my valves have needed adjusting too as miles have passed and they go for a very long, long time. The engines tell a story indeed and after so many miles, one gets to read it like a book and feel/hear and darn near become part of the engines spirit, if it had one! I've been around the stories and the bikes with failed heads and its a mess and very pricey to fix, when they come undone. Its a catastrophic mess. NO, most will never get the miles I've traveled with my Airhead and I probably could not even suggest you or they try. Its just been very god to me and I'm still smiling every time I get on the R100/7. Yes, I have other Beemers too, but this one has my heart and soul in it!:):) :wave Happy Trails, Randy13233

[James.A]

Eric, I have an R75/5 that needed to have the valves done with all the right upgrades to compensate for the absence of lead in the gasoline. It has been established that un-leaded fuel burns hotter than the old fashioned leaded variety, and I am completely confident that your bike has started down the road to a valve job. Please don't delay the necessary work.The final act of this sad play is when the exhaust valve and seat deform to the point where the valve sinks low enough to allow the spring keeper becomes dis-lodged and the valve drops into the combustion chamber when the motor is running. This is NOT GOOD. I have a good picture of a receeded exhaust valve, but I am un-able to upload it at present.