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Old 04-15-2013, 01:40 PM   #31
bmweuro OP
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I just replaced my big end bearings. I must have screwed up with the plastigauge because when I got my new bearings they were exactly the same thickness as the old ones. I mean dead on with a digital mic. And there was only the most trivial scoring in the old bearing too. I could have run them without issue. Grrr...I put the new ones in 'cause I had bought them and labeled the old ones and put 'em on the shelf.

Need a smokin' deal on some R100 big end bearings? Half price of new, precisely the same thickness.
I'll take'm.
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Old 04-15-2013, 01:43 PM   #32
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I'll take'm.
I'll put your name on them. Can get them to you fairly quickly. Do your teardown and look at the crank. If it's borked and you need to grind undersize you'll need first over bearings and mine are stock. Not real likely but worth checking. Get the bungs yet?
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Old 04-15-2013, 03:11 PM   #33
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Originally Posted by Plaka View Post
I just replaced my big end bearings. I must have screwed up with the plastigauge because when I got my new bearings they were exactly the same thickness as the old ones. I mean dead on with a digital mic. And there was only the most trivial scoring in the old bearing too. I could have run them without issue. Grrr...I put the new ones in 'cause I had bought them and labeled the old ones and put 'em on the shelf.

Need a smokin' deal on some R100 big end bearings? Half price of new, precisely the same thickness.
I tried to warn you that would happen but you were to busy advising others to do as you were doing. It will be a miracle if you didn't tear up your new bearings trying to measure them with a mic?

The white O-ring would be the first thing I looked at. I have fixed knockers like that without taking them apart at all other than fixing the oil filter setup. They were still running fine thousands of miles later so they were fixed good enough for the owner anyway. Cheaply enough too I might add.
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Old 04-29-2013, 03:56 PM   #34
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I finally had some time today to work on my own projects. I installed a mechanical oil pressure gauge and at 200 degrease(oil temp) I have 30 pounds of oil pressure and it does not fall off when I rev the motor. I'm thinking rod bearings.
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Old 04-29-2013, 03:59 PM   #35
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I finally had some time today to work on my own projects. I installed a mechanical oil pressure gauge and at 200 degrease(oil temp) I have 30 pounds of oil pressure and it does not fall off when I rev the motor. I'm thinking rod bearings.
30 is low. But what RPM did you test up to? if you got 30 at 4000rpm definitely some sort of problem.

What weight oil?

Where are you measuring the pressure and temperature?
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Old 04-29-2013, 10:18 PM   #36
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30 is low. But what RPM did you test up to? if you got 30 at 4000rpm definitely some sort of problem.

What weight oil?

Where are you measuring the pressure and temperature?
30 at idle 70 above 3000 RPM's. 20/50 BMW oil and the temp is measured at the dip stick(doesn't really matter it is just a reference) and oil pressure was right at the oil switch.
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Old 04-30-2013, 01:20 AM   #37
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Definitely low pressure across the rev range.
Have you discounted other potential leaks such as the oil filter o-ring as SS suggested?
I'd look at it before pulling heads off.

I'd check the oil filter bypass spring as well, to see that it is intact.
A piece of broken spring can find its way to the rear/front main and score the shit out of it.......low oil pressure.
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Old 04-30-2013, 10:53 AM   #38
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I didn't see any info on the history of your engine. If it is something that has run without the knock in the past this definitely doesn't apply and is probably unlikely anyway. But I thought I would throw it out as a possibility anyway. When I recently rebuilt my engine I got most of the parts from our local dealer. I asked for a set of rod bearings and they asked me did I want standard or oversize. I assumed standard since I knew the engine had never been disassembled before. Fortunately I had the rods and old bearings with me and Ozzie suggested we check the size. They were the first oversize. I was unaware and surprised to learn that some bikes came from the factory with oversize bearings. Apparently this was not very common because the shop had not sold any for over 10 years. The computer said they had some but it took Emmi to find them. Had I just asked for standard size or ordered over the net I would have the same symptoms as you. Just food for thought.

Chuck
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Old 04-30-2013, 10:54 AM   #39
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Originally Posted by bmweuro View Post
30 at idle 70 above 3000 RPM's. 20/50 BMW oil and the temp is measured at the dip stick(doesn't really matter it is just a reference) and oil pressure was right at the oil switch.
I'd do the checks 109 proposes and otherwise leave it alone. OilGuy is stating 10psi/1000rpm and you have well more than that. http://www.bobistheoilguy.com/ He also stresses flow over pressure. interesting reading.

I'm used to 60-65 psi full load running pressure on a /5. (regular castrol 20/50, measured at the switch) If you get a flickering oil light at idle then go into the bottom end and/or check the rotor clearance on the oil pump.

I always check the conrod big ends if I have the jugs off. it's worth the bolts. Basically I don't want to score the crank although minor scoring or a pit here and there won't hurt. But it's worth the bolts to make sure there isn't anything inbedded in a bearing. I also pull the pan, partially because it makes it easy to flush the bottom end when building and partially to clean it. Just a bunch of bolting and unbolting. Pain doing it on the floor, I wanna lift!.


I intend on using my pressure/temp gauges to find the lowest viscosity oils I can run. I want to be using that oil filter bypass as little as possible. This means keeping cold starting pressures as low as possible.
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Old 04-30-2013, 11:43 AM   #40
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I didn't see any info on the history of your engine. If it is something that has run without the knock in the past this definitely doesn't apply and is probably unlikely anyway. But I thought I would throw it out as a possibility anyway. When I recently rebuilt my engine I got most of the parts from our local dealer. I asked for a set of rod bearings and they asked me did I want standard or oversize. I assumed standard since I knew the engine had never been disassembled before. Fortunately I had the rods and old bearings with me and Ozzie suggested we check the size. They were the first oversize. I was unaware and surprised to learn that some bikes came from the factory with oversize bearings. Apparently this was not very common because the shop had not sold any for over 10 years. The computer said they had some but it took Emmi to find them. Had I just asked for standard size or ordered over the net I would have the same symptoms as you. Just food for thought.

Chuck
When you take it apart you always plastigauge it to check the clearances. (use the old bolts) Then mic. the journals on both parts if you can to check for roundness and size. Then go get parts (if any).

I did this recently, screwed up the plastigauge work and ended up thinking the shells were worn. Turns out they weren't, at all, at about 100k miles.

More often you replace them to loose some embedded crud rather than for wear.

If the factory screws up the grind on a crank they'll salvage it by grinding first under and then compensating with the bearings. The machines aren't blueprinted so nobody knows. You have to check everything by measuring.
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Old 04-30-2013, 05:23 PM   #41
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Originally Posted by Hookalatch View Post
I didn't see any info on the history of your engine. If it is something that has run without the knock in the past this definitely doesn't apply and is probably unlikely anyway. But I thought I would throw it out as a possibility anyway. When I recently rebuilt my engine I got most of the parts from our local dealer. I asked for a set of rod bearings and they asked me did I want standard or oversize. I assumed standard since I knew the engine had never been disassembled before. Fortunately I had the rods and old bearings with me and Ozzie suggested we check the size. They were the first oversize. I was unaware and surprised to learn that some bikes came from the factory with oversize bearings. Apparently this was not very common because the shop had not sold any for over 10 years. The computer said they had some but it took Emmi to find them. Had I just asked for standard size or ordered over the net I would have the same symptoms as you. Just food for thought.

Chuck
Not very common at all. I suspect those oversize bearings sold ten years ago at Ozzie's where ordered on mistake. I personally have changed a lot of airhead rod bearings and I have never seen one take oversize bearings. I have never heard of it from any mechanic I have ever worked with?

There is still no need to plastigauge rod bearings. Measure the journals. You don't even need a mic. .010 or .020 or .030" is plenty easy enough to determine with a vernier caliper. Wrong size bearing? They will be too loose or stuck solid after you tighten the rod bolts. Who would do that?
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Old 04-30-2013, 05:37 PM   #42
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Originally Posted by supershaft View Post
Not very common at all. I suspect those oversize bearings sold ten years ago at Ozzie's where ordered on mistake. I personally have changed a lot of airhead rod bearings and I have never seen one take oversize bearings. I have never heard of it from any mechanic I have ever worked with?

There is still no need to plastigauge rod bearings. Measure the journals. You don't even need a mic. .010 or .020 or .030" is plenty easy enough to determine with a vernier caliper. Wrong size bearing? They will be too loose or stuck solid after you tighten the rod bolts. Who would do that?
I agree 100% I'll pull the sidecar off tonight and tomorrow start pulling the top end.
The one thing I should mention-when I first started this motor after it had been sitting for almost 10 year once it warmed up it smoked like it had a stuck ring so I added a small amount of Marvel Mystery oil to the oil and to the gas. After a few miles the smoking went away so I changed the oil, but left the fiter(BMW 20/50). The next day it started to knock.
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Old 04-30-2013, 09:46 PM   #43
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My G/S developed a stuck ring after sitting on the side stand in my tight workspace for a month or more while I worked on a new seat. Smoked like a broken chainsaw. Just terrible and got even worse after warmup.

I dumped the oil and put in 1/4 liter of ATF and 1.75 of regular 20/50 MC oil. Within a minute it stopped smoking. Ran it like that for a couple hundred kms, dumped the oil again and put in fresh stuff. No problems since!

Mike at Ozzies told me about Marvel mystery oil and how it was good for oilhead fuel injectors. Never thought to add some to the motor oil. Thanks for the tip Chris.
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Old 05-01-2013, 11:06 AM   #44
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Originally Posted by supershaft View Post
Not very common at all. I suspect those oversize bearings sold ten years ago at Ozzie's where ordered on mistake. I personally have changed a lot of airhead rod bearings and I have never seen one take oversize bearings. I have never heard of it from any mechanic I have ever worked with?

There is still no need to plastigauge rod bearings. Measure the journals. You don't even need a mic. .010 or .020 or .030" is plenty easy enough to determine with a vernier caliper. Wrong size bearing? They will be too loose or stuck solid after you tighten the rod bolts. Who would do that?
This is obviously not Chris' problem and I don't want to belabor an off-topic subject but I was curious about how commonly cranks were underground from the factory and posed the question on the Airheads list. Tom Cutter and Snobum both indicated that it is not common but that it certainly occurred. Just a heads up for anyone else replacing the con rod bearings. The oversize bearing shells were not stamped with an oversize number like the automotive ones I am more familiar with. You had to look up the part number (or measure) to determine they were not standard size.

Chuck
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Old 05-01-2013, 11:45 AM   #45
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This is obviously not Chris' problem and I don't want to belabor an off-topic subject but I was curious about how commonly cranks were underground from the factory and posed the question on the Airheads list. Tom Cutter and Snobum both indicated that it is not common but that it certainly occurred. Just a heads up for anyone else replacing the con rod bearings. The oversize bearing shells were not stamped with an oversize number like the automotive ones I am more familiar with. You had to look up the part number (or measure) to determine they were not standard size.

Chuck
Anything is possible and Tom might actually know. It's just that I take all info from BMWAG, B+S, and NA with a grain of salt. It has payed off numerous times!

Chances are this isn't Chris's problem but it is very much on topic IMO.

My point is that if there ever was a crank that came out of the factory underground to spec, it would be impossible to assemble it with a different size bearing and not notice it. The rod would either rattle on the journal or lock solid depending on if the bearing was too big or too small. It would be impossible to put an oversize bearings on a standard crank. The engine wouldn't turn over. Save your plastigauge for when it matters.
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