The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Kookaburra on June 22, 2014, 10:10:07 PM
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Finally got around to doing a a compression test on 1985 R65 with 110,000 Km.
Valve lash good, battery strong, engine warmed up with 50km highway ride. So carbs off, plugs out and grounded. Results: Left cylinder went to 150 psi and right cylinder to 170 psi. Hmmm- so must be some measurement error in the tester (reading high?). Repeated for both sides and got same results. Then squirted engine oil into left cylinder and retested. It went up to 160 psi.
My diagnosis is that rings in left cylinder are shot and need replacing and I should probably do both sides when I have the barrels off to do the push rod seals.
Am I on the right track here?
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Really need to do a leak-down test before condemning them. Higher than what is considered normal compression could be due to carbon buildup in the head and on piston. But, with that "mileage" it probably wouldn't hurt to replace 'em if you have to pull the jugs anyway. You can pull the rings, insert them in the jugs, and measure the ring end-gap to see if they are worn out. On my '82 I think the top two rings were approaching the upper limit but the oil rings had huge end-gaps which caused it to be one helluva mosquito fogger after it warmed up!
I put in new rings from Moto-Bins...
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Then squirted engine oil into left cylinder and retested. It went up to 160 psi.
It is well known LORE to squirt oil into a cylinder to do a "dry" and "wet" compression test.
Sadly it is a waste of time on a horizontal cylinder, almost up there with the gentleman who was trying to convince me that I should fit valve stem seals to an airhead.
Given the cost of a set of rings (and if you are lucky enough to have a steel barrel - its even cheaper if you buy R75/7 rings) and the low price of a quick hone and given that you are taking the heads and barrels off anyway I'd give the old girl a birthday. Have the valve guide clearances checked (and if they are out of spec have them K-lined, only fit new guides as a last resort) Chuck in a new set of exhaust valves (your 50,000km "clock" resets to zero then - and if you don't know what I've talking about have a look at the piston in my photos that show the result of the head falling off an exhaust valve), re-cut all seats, check the rocker lash pads for wear and if worn have them built up and hard chromed. You top end is now good for 50,000km when you throw the exhaust valves away again, your rockers good for just about forever and your rings for 75,000 to 100,000.
Given that you do not have chapter and verse on your bike's history, the above puts you in a really good and comfortable position of assured reliability. Whilst you have the top end of the engine, do the splines and have a quick look at the clutch - changing the clutch plate is 20 minutes extra work over just doing the splines. Whilst you are in the neighbourhood, $25 for a new main seal and $50 for the tool to fit it properly is a 1/2 good idea too.
If you do take the flywheel off (because there is oil leaking out behind it, please remember to cut an allen key down and insert it into the alternator end of the crank and put the front cover back on - the idea is to stop your crankshaft from moving forward and causing the thrust bearing to come off its dowels - trust me on this, that is BAD.
Seeing as the gearbox is out at this stage, new seals (all of $10) are a no brainer, don't forget you need new drive flange bolts WITHOUT washers. Take care removing the drive flange and do not even think about using a two jaw or four jaw puller directly on the flange, drill a round piece of scrap, bolt it to the flange and then use the puller, keep the bit of scrap and loan it to your friends when they do theirs.
Finally, seeing as the bike isn't going anywhere just at the moment, pull the final drive off and replace its seal too. I remove them by drilling 4 holes in it and inserting self tapping screws, I then use a prybar on the screws to pull the seal out. There is a special tool for seating the new seal, I use a brass drift and go steady until the seal is clearly seated on its full circumference.
That's it, a full birthday and many, many trouble free kilometers in front of you. Cost of bits is less than $150 (assuming you buy a clutch plate) and will take a weekend providing you buy all the bits in advance.
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Thanks Justin and Tony,
Have ordered rings from motobins. Will decoke the heads and pistons when I have it dismantled. I have recently done the spline lube and replaced the gearbox seal with no sign of leaking from engine rear seal and clutch is OK so won't be going in there again for a while.
Attracted to Tony's suggestions for top end refresh particularly as the bike goes OK but engine sounds like a bucket of bits being shaken violently. Seeing Tony's wounded piston was also pretty sobering.
Some questions.
1. Do you replace the springs and collets when you replace the exhaust valves?
2.What about the inlet valves and springs?
3. Does anyone know of a good specialist shop in Sydney which could be trusted to do the head job and/or to reface the rocker pads?
Oh and BTW if the wet test on a horizontally cylinder is not workable how come the compression test went up 10 psi? I was meticulous in using a syringe with a tube to spray oil all around the the subject area.
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Hone nikasil-plated barrels?
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Hone nikasil-plated barrels?
I'm scratchin my head too, Monte. Unless there was a change back than the 81+ bikes have aluminium cylinders with Nikasil plating. At 110k km I wouldn't expect the bores to be worn (damaged would be another thing).
There are places out there that can bore a Nikasil plated cylinder and re-plate it to any reasonable size. Vintage kart racers and experimental aircraft folks use this type of service on their small two stroke engines. Probably $$$
As for all the rattle... have you stuck a timing light on the bike? The chain will make a racket when in dear need of replacement.
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Unless there is damage to the cylinder, I see no need to hone.
My R65 showed the rings within specs for end gap at well over 100,000 miles.
Valves may need grinding or replacing if bad, but otherwise, maybe a little grinding compound and time may raise the compression. Noise can come from many places. It is always cheaper (and better) to find the culprit before starting to throw unneeded parts at the problem.
Bob
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Hone nikasil-plated barrels?
Never, although a bit of a rub with medium sandpaper does help. I didn't bother to look back and see what year his r65 was and I did say "if you are lucky enough to have steel barrels".
I guess for the pedants here I shoudl also add that if you have Nicklasil bores, you can't use the cheaper R75/7 rings either, you have to use R65 rings for Nickasil bores.
A very light hone (about 5 to 10 seconds worth in the hands of a skilled operator) never goes astray.
Many, many people are paid up members of the "my rings were not worn out and bore was nice and clean so I put new rings in and now I am burning more oil than I was before I changed the rings and this has been going on for 20,000km" club.
You hone the cylinder to break the glaze so that the rings do wear in and establish a good seal.
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Thanks Justin and Tony,
Attracted to Tony's suggestions for top end refresh particularly as the bike goes OK but engine sounds like a bucket of bits being shaken violently. Seeing Tony's wounded piston was also pretty sobering.
Some questions.
1. Do you replace the springs and collets when you replace the exhaust valves?
Not if yours are in good condition, a quick check that all the springs have the same free height will quickly tell you if any have lost their "springiness" When you remove the collets you run your finger around the collet groove to ensure that there is no horrid ridge that will damage your valve guide when you try to press it out (by the way, if there is a ridge the blood running form the tips of your fingers is frequently the first indication you have, they tend to be very small ridges, but oh so very sharp) If there is a ridge throw the colletts on principle (they may well be perfectly OK, but they cost pence so why take the risk?
2.What about the inlet valves and springs?
They do not get heat cycled to anywhere near the same extent as exhaust valves, they are good until they are mechanically worn out.
3. Does anyone know of a good specialist shop in Sydney which could be trusted to do the head job and/or to reface the rocker pads?
Ring Gowanloch and ask them who does theirs.
Oh and BTW if the wet test on a horizontally cylinder is not workable how come the compression test went up 10 psi? I was meticulous in using a syringe with a tube to spray oil all around the the subject area.
How many CCs of oil did you pump in there? Oil is incompressible so its presence in the combustion chamber at TDC on compression stroke would tend to raise the compression pressure. Also, to be fair, if you went to the trouble of distribution the oil around the piston crown you may well have got enough in the right places to make a difference, but I'd go with the increase being due to the amount of oil you put in there.
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This thread here is a good read so keep it coming, boys! Diving into piston ring change and valves is the next in my list of future works.
Just wanted to share my appreciation even when I have nothing to add to the topic [smiley=beerchug.gif]
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With the Nikasil cylinder bores, it is not uncommon to still see original hone marks even with 10s of thousands of miles on the engine. Usually, a little scrub with some of those scotch brite scouring pads to remove any crud is all that might be needed, unless you've dropped a valve and gouged the cylinder lining. The iron liners of the 79-80 bikes definitely should get a light honing. The iron lined cylinders can use the hard chrome rings, but the Nikasil cylinders must use the 'soft' iron rings
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Thanks gurus your replies, extremely helpful as always.
I have the Nikasil barrels and therefore will be scotchbriting not honing. New timing chain recently so thats not the source of divers noises.
So it seems, replace the exhaust valves for peace of mind and collets because they are as cheap as. Will talk to Gowanloch about who does their recon jobs. They appear to be ace Ducati specialists but I should be OK as I aready have a couple of Ducati parts such as neutral and oil pressure switches on the bike.
Leakdown test would have been good but didn't have the bits to do it.
Re the compression test. I didn't use more than a few cc's of oil for the wet compression test but it was carefully distributed so I think the jury is still out. I will measure the ring wear and report back on the evidence when I pull it down.
Now waiting for the bits to arrive!
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Hijacking the topic here to keep the question in the same frames:
Compression test results:
Left cylinder 115psi
Right cylinder 120 psi.
Now the question is - how many miles would you guess the engine has done with these results? The engine does burn a bit of oil, not too much but revving it up I can see a trail of smoke and my back wheel is covered with ash.
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I did a compression check on my '81 R65, just before the engine quit a little over 2 months ago .
I had 132 psi and 138 psi, this bike has around 90,000 miles, 145,000 km on it .
The valves and seats were replaced at around 45,000 miles, 72,000 km .
I'm the original owner, so I know the engine oil and filter were replaced frequently, probably too early in most cases ,.
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Those compression figures are close to the borderline of the good and poor ratings (121 PSI) and if it's an 81 model year it should have Nikasil type cylinders which are reckoned to wear very little so I'm thinking a significant mileage. I'll guess 70,000 miles.
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The problem is - I do not know it myself. The bike odometer is 32000miles but the engine no and frame no do not match. So it might be that a swap with the engine has been made (a bad sign).
Could it be that by "trashing" the engine the compression rate figures could go down as well?
And I would not put my bets that the valves etc. have ever been changed as the bike has been properly abused as shown by other parts of the bike.
I do have new rings, gaskets etc on hand but I can not take the left hand side muffler connection to the cylinder off. It seems the only way is to cut it off which I am a bit weary to do it properly.
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Not withstanding Tony's comments about a squirt of oil in the cylinders not being quite so applicable on a horizontal cylinder, did you try it anyway to see if the compression figures improved. Also assume you did the test with engine hot and carbs off or throttles open and pistons lifted.
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I have not tried oil. But other than that I did the compression test as described.
The spark plugs were burning hot when I removed them and grounded them on the cylinder.
I opened the throttle fully and pumped the starter for 10 second for both cylinders.
I could squirt a spit of oil in there to see if I get any change at all and report it back here tonight.
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Results of squirting oil into cylinders.
Left - 115 to 130
Right - 120 to 128
So oil did affect the results somewhat. Not a huge leap but still noticeable. Left cylinder compression, which had lower results increased much more than right cylinder.
If I am correct then oil indicates only piston ring wear and tear, not the valves?
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If I am correct then oil indicates only piston ring wear and tear, not the valves?
That's the usual interpretation.
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I opened the throttle fully and pumped the starter for 10 second for both cylinders.
But did you lift the slides? Spinning the engine with the starter won't make enough vacuum to lift them up and the engine will be starved for air, lowering your compression test figures.
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Lift the slides? Do you mean pulling the throttle cables as far as they come out of their brackets to get the butterfly slide opened up?
these compression rate figures are already low. Do you want to tell me that I have a bucket instead of a piston in there ;D
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Twisting the throttle opens the round, flat butterfly valves that rotate with the throttle shaft. The slides (with the diaphragm and jet needle) are indirectly controlled by vacuum from the intake port and slide vertically in the carburetor body. There will not be enough vacuum to lift them when spinning the engine with the starter motor.
To properly test you need to hold the throttle wide open and hold the slide up while cranking, or just remove the carburetor altogether.
Your compression figures will go up, not down!
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If you remove the intake tube from the carb, you will see a the slide, it moves with engine vacuum not the butterfly plate that the throttle cable moves, without the engine running, it almost blocks the carb throat and restricts airflow .
I also operate the starter for about 45 seconds on each cylinder .
Make sure your battery is fully charged before you do a compression check .
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Hmmm, I dunno 'bout cranking 45 seconds - seems like starter abuse! I crank it over about 10 revs and important do do the same number of cranks on each side. You can watch the gauge and it will "squirt" a little higher with each turn but IIRC after about 5 revs you don't get much more to speak of...
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Hmmm, I dunno 'bout cranking 45 seconds - seems like starter abuse!
Inclined to agree. I reckon that 5 compression cycles is more than sufficient. I also think that given the vagaries of gauges, technique etc that the best advice is to look to see that there is no significant difference in the measured compression between the cylinders.
if the difference is small and the bike is now chewing oil, or having trouble outrunning grannies on electric mobility chairs, I'd be inclined to leave it alone, unless i was goign to pull the heads off to do the valves, in which case a set of rings is a no-brainer.
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I always completely remove the carbs to eliminate any intake restrictions from messing up the results - I think it is simpler to do rather than holding the butterfly open and making sure the carb slide are fully up -- otherwise your test results will be lowered/inaccurate.
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properly test you need to hold the throttle wide open and hold the slide up while cranking, or just remove the carburetor altogether.
Your compression figures will go up, not down!
You were correct on this. The results were different. I removed the carbs totally and pumped the engine on twisty roads so that the engine was completely hot before commencing the test. All the abovementioned requirements for the test were fulfilled as well (throttle wide open, battery full, crank the starter for 10 seconds - i could still see some movement in PSI after 5 starter cycles) Results are:
Left - 125 psi
Right - 130 psi.
I am leaving myself out of the debate about oil in horizontal cylinders. I can only report what my findings are.
Left - from 125 to 150!
Right - from 130 to 147
So percentage wise, the left cylinder with lower compression rate, increased much more than the right cylinder. Nevertheless - cylinder compression rate increased 21 psi on weighted average.
Question - could these compression rates mean that my bikes 32k milage (50k kilometers) could be correct under certain circumstances?