The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Adamastor on October 04, 2009, 04:50:02 PM
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Hi there!
A friend of mine just gave me a compressor tester and I tried it on my R65. Results (with throttle fully open):
LS = 145 psi
RS = 115 psi
That's quite a difference.. i searched the internet but did not find what is the factory standard and what is the minimum acceptable for a R65 head.
Is 115 too low? Is it bad for so much difference between the two cylinders? If I want to get the right side better should I look for new valves or new piston rings?
Cheerio!
Sergio
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115 seems low check the valve clearances on that side before you wade into stripping it, mine is 145 on both sides checked after rebuild including piston rings 600 miles back.
Lou
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Straight from the BMW shop manual : above 142 psi good, 121-142 psi normal, below 121 psi poor .
The right cylinder needs some work .
First off, have you done a valve clearance check/adjustment, if you haven't done that yet, I would check it, you may have too close of a clearance on a valve, and it may not be closing all the way .
If the compression tester has a separate part that threads into the spark plug hole, has a 'quick disconnect' on it, you can connect a compressed air source to it, and with the valves closed, put some pressure in the cylinder .
If the piston rings are worn, you should feel air coming out of the oil dipstick hole .
If a valve is the problem, you may need to take the intake tube off, and listen/feel for air coming out of the intake .
The exhaust valve is a bit more involved, you may be able to feel air coming out of the muffler .
But the only real way to know for sure, is to remove the exhaust from the problem cylinder, and check for air leakage then .
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I actually had just re-checked the valve clearances because I had changed the rocker arm adjuster bolt...
Tommorow I will do the oil and intake checks to try to see If I figure out where's the problem...
This cylinder plug was usually more oily/dark than the other one and the carb mixture screw didn't do much difference. That's consistent with low compression, right?
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What year is the bike ?
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1985
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Ok, I have been working on the bike and done the tests you gave me...
Pressure goes no more than 118 psi without carb. I left the pressure tester some time on the sparkplug hole and there is no slow leak. Pressure was stable.
I opened the oil filler hole and while cranking I felt air being sucked in and sucked out as the cylinder goes in and out, but that should be normal, right?
I managed to take out the exhaust nut, but the down tubes are really hard to disconnect from the muffler and the horizontal tubing...
Should I play a little with the valves clearance in order to see if compression alters? I had done the valve job yesterday with .10 inlet / 0.2 outlet.
Should I buy new rings for this piston? Taking the cylinder out should be not that hard after I manage to remove the exhaust tubes... Messing with new valves should be harder for a non-experienced home mechanic like me...
Meanwhile not everything is bad, I discovered that I still have splines and have cleaned/lubbed them :) (they were clean but very dry)
Sergio
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When checking the cylinder for leakage, using compressed air, you don't turn the engine with the starter, you just put air in the cylinder, and then feel, or listen for air coming out of the dipstick hole .
You need both valves in that cylinder closed, so pressure can build up .
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Hmmm back from the garage once again... I have no chance to put compressed air on the cylinder...
Anyway, before thinking of buying rings and valves I went to the garagem and re-done the valve job:
Now I have 125 psi on the worst cylinder!
I assume since this is acceptable (even thou the other cylinder has more compression) isn't it?
(meanwhile also lubed the rear splines... )
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If the engine is running good to you, keep riding it, I would keep a close eye on the oil level to see if you have higher than normal oil consumption .
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I have only ridden about 1500 km on this bike, and yes there is some oil consumption. I am not sure how much, but a bit more than I thought it would be normal..
I will keep on checking and maybe later this year buy some new rings for this cylinder.
Right now I am waiting for the front disc and the dyna coil for taking her out to the road again...
Apart from the 3 rings I would also need the cylinder to engine gasket and maybe the rocker arm rubbers, right?
Regards and thanks for walking me on this :) This forum rocks! :)
Sergio
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There's also an o-ring on the cylinder base, and two small o-rings that go on the cylinder hold down studs .
Oil supply for the rocker arms come up around the studs into the cylinder head .
Also be sure to use a head gasket sealant of some sort in the area of the studs, if you don't, most likely you'll develop a leak here .
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Motorworks sell a kit for the head includes all the seals ect scroll down the page.
http://www.motorworks.co.uk/bmw/products/product.php?f=i&code=BA_15_20_BA_70&shnew=New&model=R45%2F50%2F60%2F65%2F75%2F80%2F90%2F100+%282+valve%29&shnewcode=15&part=Engines&sub_part=Top+end+gasket+sets&modelcode=20&partcode=BA&source_code=BA_15_20_BA_70&header_text=&header_text_image=0
Lou
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The other way to see if it is the rings leaking or the valves leaking is to put a small amount of engine oil down the sparkplug hole before doing the compression test.
If it is the rings that are worn, this should raise the compression, if it is a valve problem the compression will read the same as it was without the oil.
I'm not sure how well this works on a horizontally opposed engine, maybe you will have to lay the bike over to get the oil to run around and seal the rings before standing it up for the compression test?
If it was my bike I would budget on replacing the rings on both sides, even though you have good compression on one side. Just doesn't seem right to only do one side.
Cheers
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125 is within acceptable range, though I would think that if one cylinder has 20 PSI better compression readings it is still going to be doing a bit more work, and the engine won't be quite as smooth as it could be.
So what did you set the valve lash clearance to be on the low cylinder to bring up the number?
I'd ride it as others have suggested, and keep an eye out for oil consumption. Over the winter when we cannot ride over here, I'd plan to do the rings, and check over the valve seats on both sides, too - if the heads are coming off, may as well get the valves done IF they are in need of it.
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125 is within acceptable range, though I would think that if one cylinder has 20 PSI better compression readings it is still going to be doing a bit more work, and the engine won't be quite as smooth as it could be.
So what did you set the valve lash clearance to be on the low cylinder to bring up the number?
I'd ride it as others have suggested, and keep an eye out for oil consumption. Over the winter when we cannot ride over here, I'd plan to do the rings, and check over the valve seats on both sides, too - if the heads are coming off, may as well get the valves done IF they are in need of it.
I had the intake valve clearance a bit too narrow (I had seen that these later airheads could use 0.05 mm on intake, so I had it between 0.05 and 0.1mm)). Now I have 0.10mm..
I ordered the kit of new rings from motobins and since I wont be running (waiting for dyna coil) I will do the ring job :)
It wont hurt to have new rings, right? Besides that my rocker arm rubber inserts were leaking oil, so this will be usefull...
:)
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The other way to see if it is the rings leaking or the valves leaking is to put a small amount of engine oil down the sparkplug hole before doing the compression test.
If it is the rings that are worn, this should raise the compression, if it is a valve problem the compression will read the same as it was without the oil.
Hi!
I have just done this test with a bit of oil down the sparkplug hole, and got an impressive 150 psi compression. I am glad I ordered the new rings already ehehe :D
thanks for the tips!
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Hi there!
I am a bit disappointed since I have just changed the rings on the low compression cylinder, and after torquing everything up and cranking the engine I got the same compression I had before :(
What could be wrong then? There were no scratches on the cylinder neither on the piston (on its travel) only the top (combustion chamber) had some marks... I also de-carbonized the chamber..
I am a bit clueless and tired (took me 3 hours to do this job on only one cylinder...)
I need you airheads detectives opinion on my "mystery" :)
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About the only other possibilities after ruling out the rings and cylinder, are intake or exhaust valves not sealing on their seats, or cylinder head gasket leak .
You could try some soapy water on the cylinder head/cylinder gasket joint, and then rotate the starter, and see if you can see any bubbles, or foam develop .
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I got all new gaskets and also liquid sealant on the cylinder to engine surface. I noticed there wasn't the big O-ring of the cylinder base. Now I have one there...
Apart from the rings, what else could be wrong with the cylinder/piston?
Regards,
Sergio
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And one more thing, is there an easy way to clean the valves and their seats? I cleaned the chamber but the valves were closed...
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I wouldn't think the cylinder is the problem, as it should be a 'nikasil' cylinder, kind of like a chrome plated cylinder, unless the plating is missing in spots, I can't see it being worn .
For the piston to be worn that much, I think it would be obvious by just looking at it .
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Hmm one more thing I observed... I tested the compression with no carburettor and no exhaust tubes, and I saw on the outake kind of a cloud on each cycle... I thought that it could be remains of oil or dust on the exhaust tube, but maybe it should be only clean air coming out, right?
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I went to the garage to look back to the cylinder... there are some imperfections near the edge, can this be the culprit?
Hi-resolution galery: http://img198.imageshack.us/gal.php?g=igp9867.jpg
The bad spot:
(https://bmwr65.org/smf/proxy.php?request=http%3A%2F%2Fimg203.imageshack.us%2Fimg203%2F2183%2Figp9878.jpg&hash=2078dffd9e37ac1e6e284699edf51c008f193883)
The piston head also has some marks, but on the top, not on the lateral walls...
Please give me your expert opinion... Is this the culprit for not having good compression?
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I think you have found your problem .
I can't quite tell form the photo, but it appears that there may have been a valve issue on this cylinder .
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But if you look to the above photo, you see that most the scratches end before the "reach" of the first piston ring... would they still be noticeable?
If so, what would be the solution? Rebore + new piston? Is it easy to get new sized pistons? Rebore will kill the nikasil finish?
So many questions... I know I am a pain in the $%# :p Sorry!
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How does the cylinder head look ?
This has the appearance of something got loose and banged around the cylinder (like a valve head), not a good thing .
I don't think you can bore out a nikasil cylinder, maybe someone else knows for sure, and can comment .
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Hmmm what is the cylinder head? (sorry) Apart from the scratches you can see on that photo, the rest seems ok, no scratches or marks...
One more question: Can you use a 1980 cylinder with this engine / head?
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Oh, the head is where the valves are (lol)... I took a picture:
(https://bmwr65.org/smf/proxy.php?request=http%3A%2F%2Fimg260.imageshack.us%2Fimg260%2F451%2Figp9875.jpg&hash=28896af49ac559255be582460e2a0b1dc9609c06)
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I think a rebore is required haveing seen the cylinder and fit the aproprate oversize rings.
Lou
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Hi Lou, can you rebore a nikasil cylinder?
On the Moto-Bins site they have that the after 1981 rings kit say: 650cc R65 1981 ON (NO OVER SIZE)
They don't even sell new/refurbished nikasil cylinders... :(
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Nikasil bores aren't able to be re-bored - the lining is very tough, but very thin. IF they aren't damaged from something destroying/gouging the surface, they'll stay perfectly smooth for > 150K miles, easily. But unfortunately, this makes them "disposable" if the surface does get damaged. I haven't yet found anyone who can re-apply a Nikasil lining- there may be a place which does this, but I don't know where it is.
The Nikasil cylinders are definitely better at heat dissipation than the iron lined ones, and virtually don't wear out, but they are a bit like those non-stick cooking pans.
I'd look for a possible source of use nikasil cylinders like ebay, etc. as your best option if you end up replacing it. You could switch to the 78-80 iron lined cylinders, but would also have to switch pistons and rings for those cylinders as well. I also don't know how well the large valve heads work with the older style cylinders&pistons (critical factor would be valve head/piston head clearance or squish clearance).
The piston head does look odd - it does appear like there are valve-head shaped "dents" in to crown. Usually when a valve head separates in a running engine, the damage is more severe and often there is a hole punched right through the piston top. It is hard to tell what happened to that cylinder in the past, but it certainly wasn't a happy thing.
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It is certainly my understanding that you can't rebore a nikasil cylinder, hence why no oversize rings are available. My guess is that you would have to get it bored oversize and sleeved back to standard.
Then you would have one nikasil cylinder and one iron so I don't know what other implications that has.
Your cylinder bore certainly does look damaged above the rings and whatever did it must have damaged the bore lower down to some extent. I think I would be searching for a low mileage cylinder as they are not supposed to wear out.
It may be time to take the bits to a BMW expert for some technical advice?
Cheers Bruce
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I am asking if you can mix a pre-1981 barrel/piston with a post-1981 head because I have the chance to buy a pair of pre-1981 barrels+pistons.
Apart from buying new rings for these pistons, would it just be plug and play? Do the heads bolt in perfeclty?
Thanks once again...
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I am asking if you can mix a pre-1981 barrel/piston with a post-1981 head because I have the chance to buy a pair of pre-1981 barrels+pistons.
Apart from buying new rings for these pistons, would it just be plug and play? Do the heads bolt in perfeclty?
Thanks once again...
A very good question i would say yes as i cannot see BMW retooling to alter the engine caseing and everything else but to be sure i will ask Andrew at Mollsprings if he doesnt know he will know how to find out ill get back to you tomorrow on this one
http://mollsprings.co.uk/
Lou
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Lou, it would be great for you to know that for me :) Could save my day :)
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I am running post 81 heads on pre 81 barrels with pre 81 pistons (1st oversize atfer a rebore at 94,000 miles). So there are no clearance issues - I have almost 15,000 miles on them.
I would say however that you are introducing a significant amount of weight....you will know about it when you campare the weight of the two. Iron is heavier than Ally. I would be looking for a new nikasil barrel if I were you.
Steve H (Rev. Light)
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Im reliably informed there interchangeable if weight is an issue go on a diet!!
Lou
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Thank everyone :) that is good to know, I am however now speaking with someone who knows someone who might have a nikasil barrel in good shape... let's cross fingers :) I think it also has a mating piston, and I might buy it too. Mine has all those marks on the crown... it could be bad, right?
Regards
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There's an outside chance, that with the piston hitting an object, it may have been cracked in the process, and it may not be readily visible to the naked eye .
I would seriously consider replacing the piston as well, if you can do it .
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Just finished assembling the "new" cylinder and piston with the new rings and got her to fire ok (lots of smoke).
Tomorrow morning I will do a small test ride, so I can balance carbs with a heated engine.
Any special advices for new rings/cylinder/piston break in? I usually simply avoid high revs and try to vary revs the most I can (city/small roads).
I am not sure I still know how to drive the BMW eheheh It's been a while since I last rode it (and unfortunately came back home on a trailer). I am crossing fingers so that It wont be raining...
Apart from the "new" piston/cylinder/rings it also has new coil (Dyna Coil) and new CDI. I only miss a new hall sensor to have a brand new ignition system on my R65!
Do I/Should I change the hall sensor? Already seen on the web it is not the easiest job on earth, but can be done...
Regards,
Sergio
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Good to hear you got all of the problems sorted out !!
Break in the rings just like you stated .
As far as the Hall sensor is concerned, it's not an overly difficult job, but if you break something in the process, no individual parts are available, unless you have a 'donor' 'bean can' to cannibalize parts from .
I personally wouldn't touch it .