Little bits of power loss

[Luke D.]

Good day all,

  I have been riding my 82LS quite abit this year after having it tuned up and running like a top.  Well, I went for a cruze yesterday and notice that my bike wasn't as pepy as it usually is.  From stop to about 6000 RPMs is just fine but about 6500 to about 7000 is alittle noticeable and 7000 it is just not working.  I know the power range for the 650  stops around 6250ish (max HP) but she didn't want to run up much higher than that.  So my question is why do you think that is happening?  Could the lifters need to be adjusted? (had them done this Spring) The bike has been sitting for about two weeks because of crap weather and Mountain biking.  I only put Premium gas and if I can Non-Oxy.  I believe that is what is in the tank now.  So I don't think it is gas.  Any help would be appreciated.  Thank you all and have a great day.

[wilcom]

The closest one I have owned to yours was my 82 R80 and it was always the valves when I would get a lil shaky on the top end..... I'd adjust them up and it would again spin back to 7,000.... Was that a year for valve recession?

[Luke D.]

Wilcom,

  Thank you for your reply, I am sorry but I don't know what valve recession is.  I looked into my Clymers books at the valve clearances and found two different answers.  One Clymers (big one) says the intake should be .004 but in the other one (small one) it says .006.  My gauges only go down to .006 do you know which one it is supposed to be?  I know you had an r80 and not the r65 but any help helps Thank you again for your help.

[wilcom]

Per Snow Bums site : http://www.bmwmotorcycletech.info/setvalves.htm

"On all models except the R45 and R65, I set the clearances to .0045" intake, .0085" exhaust, with pressure on adjustor end to take up oil film slack. That is equivalent to an easy smooth fit for the .10 mm and .20 mm metric feelers, same for .004" and .008" feelers.   The R65/R45 models probably should have the valves set a wee bit looser, .006" intake and .010" exhaust is fine.  There is nothing wrong with using .006 and .010 on all the various models, actually, and a case can be made for some slight benefits, at the expense of a SMALL amount of noise and potential wear. Be VERY sure you are not only at OT, but are at OT on the compression stroke for THAT cylinder. "

[Barry]

I don't know what valve recession is

Valve recession is excessive wear of the exhaust valve seat due to micro welding which in theory should have became prevalent when leaded fuel was withdrawn. The symptoms are rapid closing up of the valve clearance. BMW had a go at pre-empting the problem in 1980/81 and stuffed up with seats that didn't wear but had a poor heat transfer coefficient which in some cases caused the exhaust valve to overheat and suffer from plastic deformation. That also caused the valve to recess into the seat and the symptoms are also rapid closing up of the valve clearances.  

In 85 they eventually resolved that problem by more appropriate choice of seat material but not in time for your 82 model.  Some have had to replace the seats or have replaced them as a precautionary measure but it's not necessarily an inevitable problem unless the bike is habitually ridden hard at sustained high revs.  Other 82 owner will comment on what they have done or not done.  

Owners of 79 and maybe some 80 models will have the original cast iron seats which in theory should have been susceptible to the micro welding valve seat recession but in practice many have been just fine on unleaded fuel and no after market additives. Mine are OK on the basis I see no measurable recession and I have never used an additive.

Bottom line as a minimum is to accurately set the valve clearances and record the values for reference at the next service to determine how much they have changed. The actual clearance to choose is less important than setting them consistently for the purpose of determining if valve clearances are closing up. Putting thumb pressure on the pushrod end of the rocker to take up and slack in the valve train is important for accurate and consistent setting.

Personally I go with Snowbums slightly wider settings.

[georgesgiralt]

Guys,
On my '82 leaflet, they gave 0.05 mm gap for inlet and 0.20 mm gap for exhaust.
Then I heard they changed to 0.10 mm for intake valve lash and stayed at 0.20 mm for the exhaust.
The local Guru says it is better to go up to 0.15 mm for intake valves and 0.20 for exhaust valves.
I tried this last couple of values but it is definitely too noisy for me. So I stick with the .10 and .20 mm gap.
Watch out the closing of the lash as it may also indicate the valves elongating before breaking ! And this is a very different and costly matter.
I've been told to change the valve train every 60 000 to 90 000 km. I've seen a motor were the exhaust valve broke right at the tulip. The tulip welded itself into the piston and the valve stem acted like a sewing machine needle and perforated everything..
Not a nice look. The whole engine went to the garbage bin as there where metal bits into every recess and oil conduit.... Impossible to clean.
It is good practice to measure the lash before adjusting it. This way you know if it is clising or opening or staying stable.
I change my oil every 5000 km (a lot of urban commuting) and have a look at the valve play at oil change. This way I hope I will prevent catastrophic failures. So far, so good !

[mrclubike]

I have no valve rescission and also find the .15mm intake clearance very noisy
I am going to ,10mm the next valve adjustment check
R65 mfg 11/81  

[Barry]

I know I'm getting a little deaf in my old age but I don't find the wider clearances of 0.06" and 0.010"  (0.15mm 0.025mm) at all noisy.

I do use firm thumb pressure on the rocker and set the clearance for a relatively tight sliding fit on the feeler so that I can be sure that I end up with a clearance that is definitely no more than the set values.

[Luke D.]

Good day/evening everyone.  The eternal Minnesota is finished and so I finally took the time and adjusted the valves.  First I would like to say thank you everyone for you help with clearing some things up for me.  I checked and set the valves to .004 and .008 intake and exhaust.  I then proceeded to enjoy a 30mile ride(first one of the season)     I noticed when I was on the freeway that I still have the lost of power at the higher rpms.  I don't hear or feel anything unusual.  Do you think maybe the carbs are "not set up" for the higher revs?  or maybe it floods itself at those revs?  I am just thinking of things that may explain why this happens.  Thank you in advance for anyone and everyones help.

[Luke D.]

Good day everyone,  I took my bike to and from work today and I noticed something.  When twisting the throttle it would rev up like it should until about 5000-5500rpm and it would not want to rev any higher.  It would kinda bog down until I backed off the throttle and then it would start reving up again.  Is it possible that the carbs go out of sync when the hit the higher rpms?Thanks for your help and have a great day.

[Barry]

When the engine pick ups after the throttle is relaxed slightly that is the classic sign of a weak mixture.  I'd start by checking float levels.

[Luke D.]

SCHAWEEET, thank you Berry, I thought something with the carbs might be amiss but I am not very good at carbs.  I would assume the correct information will be in my manual?  I will have to check that out.  Thank you again Berry.

[marcmax]

Luke I had something similar on my R65LS when I first bought it . As a matter of fact I got a decent price because of it. It would cruise fine until I got to around the 5000 rpm range. That was usually approaching highway speeds. I never noticed if going up through the gears as I tend to shift early and not run it up to higher rpm's while accelerating. Anyway when I got to around 5000-5500 rpm the power just fell off, almost like it had a governor on it. On the advice of a knowledgeable local airhead I opened the carbs and checked the diaphragm with a bright light from behind. Sure enough there was a series of tiny pinholes causing the carb to not open fully and give the no power feeling. Replaced the diaphragms and its been running fine ever since.

[Luke D.]

Marcmax, thank you for your reply.  I phoned the BMW mechanic I bring my bike too to see what his thoughts were.  He looked at what he did last year for a tune up and asked me if I set the valves (which I just did Tuesday).  Then he mentioned checking the diaphragm!!  So if two really smart people say that then I think I will check those bad boys. Anyway long story short I will check those tonight and see what I find.  Thank you for your help and have a great day.

[marcmax]

Just as an FYI, if you do find an issue with one or both of the diaphragms replace them with oem Bing parts. There are some aftermarket diaphragms that are a little less expensive but the rubber is a tad stiffer and you will just introduce a whole new set of problems. Please don't ask me how I know.