R100RT, '81 needs valve job.

[mbrause]

I have over 100k on my motor. Just took the compression and it was bad (90). The valve adjustments have always seemed ok. I did not ride it last year and now I really notice the lack of top end power. I have read the adds for Bob’s BMW and they claim have to what it takes. Do they really? I don’t want my heads messed up but don’t know where to go. Any recommendations would be appreciated.
Thanks
Manfred
N. Yarmouth, Maine

[20774]

What procedure did you use to measure the compression? Warm motor? Carbs off or slides pushed completely open? A leak down test would give you a better idea of where the problem is.

Of course 100K is great mileage, and on a 1981 with the valve clearances holding. The "word" is that the '81-'84 would sooner than later have valve problems...the operative word was sooner. I'd say you got your money's worth out of it!!

Kurt in S.A.

[mbrause]

The motor was very warm, just got home from work - 20 miles. I did not do anything with the carbs other than to hold the throttle open. I could do a leak down but I would need to add a fitting to the compression gauge line for the air compressor fitting. So if I put in 100# how long should I expect to it stay or what rate of bleed down is acceptable?
thanks
Manfred

[rkildu]

I sent my heads to Leo Goff at Memphis Motor Works. It took just over a week to get them back, of course I am only a couple hundred miles away. They looked great and are performing well so far. Price was reasonable.

leogoff@memphismotorwerks.com

He has a web site so you can check pricing.

Rod

[20774]

The motor was very warm, just got home from work - 20 miles. I did not do anything with the carbs other than to hold the throttle open. I could do a leak down but I would need to add a fitting to the compression gauge line for the air compressor fitting. So if I put in 100# how long should I expect to it stay or what rate of bleed down is acceptable?
thanks
Manfred
If you have Bing CV carbs, just holding the throttle open isn't going to give you an accurate reading. The slide in the carb is controlled by the vacuum created by the in-rushing air, and at starter cranking speeds, the slide is not going to rise appreciably, restricting the flow of air coming into the cylinder, giving you false readings on the compression test. One way is to remove the tubes providing air to the cards and use a piece of wood, etc., to prop open the slides. Or, after removing the tubes into the carbs, loosen the clamps holding the carbs to the rubber tube on the outlet side of the carb and pull the carb away from the head, leaving it hang temporarily by the throttle/choke cables. Then there would be no restriction to the incoming air.

As for a leak test, I recently purchased a unit from Harbor Freight...I think it was $50 or so. It seems nicely built. It has everything ready to go. One of the gages is graduated in % leakage. I used it to check out my /2. I had around 10% leakage and it was all past the rings...I could hear air escaping from the oil fill hole. I didn't hear anything coming through the carb (intake valve) or the exhaust (exhaust valve). I think a value more in the 2-5% range is best. I don't know enough about how the % value is computed in terms of time for the loss of pressure, etc. That's why I got a setup to give me the value directly.

Kurt in S.A.

[RandyB]

I sent my heads to Leo Goff at Memphis Motor Works. It took just over a week to get them back, of course I am only a couple hundred miles away. They looked great and are performing well so far. Price was reasonable.

leogoff@memphismotorwerks.com

He has a web site so you can check pricing.

Rod
Great advice. I took it and my heads were redone and back in 4 days. Price was reasonable. They look great. Now if I can just get home to install them. Thanks for the tip Rod.

[flash412]

I could do a leak down but I would need to add a fitting to the compression gauge line for the air compressor fitting. Get your hardware set up with a T. (I bought one at Sears for about $3-$4.) You need to have the hose that goes into the spark plug hole, the gage and the compressor. If you use a quick disconnect on the hose to the spark plug hole, life is easier.

With the hose to the motor disconnected, set the output of your compressor regulator so that the compression gage reads 100 (you don't CARE what the gage on the compressor reads). Remember that you have to come UP to this value. If you turn the regulator down, you will need to bleed off the system in order to get an accurate reading on the gage.

With the cylinder on TDC on compression, plug the hose into the T. The gage will immediately drop. The difference between the reading and 100 is the leakdown percentage. If it drops below 80, you have serious issues that need attention. If it is above 90, things are good. If it drops below 80, get a mechanic's stethoscope (or stick the handle end of a long screwdriver against your ear) and poke around. You can often determine if it is one valve or the other or even the rings that are leaking the most.

The motor MUST be dead-on TDC or it will spin.'
It must be on TDC compression or else your leak will be 100%.

[SinNH]

I have over 100k on my motor. Just took the compression and it was bad (90). The valve adjustments have always seemed ok. I did not ride it last year and now I really notice the lack of top end power. I have read the adds for Bob’s BMW and they claim have to what it takes. Do they really? I don’t want my heads messed up but don’t know where to go. Any recommendations would be appreciated.
Thanks
Manfred
N. Yarmouth, Maine
Agree with the carb removal for comp test.
Head work ,, I DO NOT reccommend San Jose BMW, lied over the phone, took two and half months :banghead :banghead , and one head had to go back.

[Bokrijder]

Leo Goff does excellent work. He has been honest with me in projecting a completion date. Keep in mind that the required repair time will depend on the condition of the heads.


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