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Old 01-01-2013, 05:27 AM   #16
photomd
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IMHO, look for something objective. That's what the compression and leak down test is telling you. If they're off, use that info to investigate. As for the breather system, I'd guess you can pull the right spark plug and carb and see oil or carbon build up on the right side as compared to the left if the breather system is not working correctly. My guess is that the cold, thick oil is blowing by the breather system. As it warms up, the blow by decreases, but I'd want to find more info before replacing parts and fixing it. As Big Sid once said, the bike is telling you what's wrong, you just have to listen. In my garage, I always have to "listen" several times before I get it right.
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Old 01-01-2013, 05:30 AM   #17
disston
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The crank case breather controls the pressure in the crank case. The original design on our bikes was a disc that was spring loaded, sits in front of air filter next to starter. A more modern one can be retro fitted. They work quieter, no Turkey Gobble sound, and are supposed to work better. The modern one is a reed valve.

The breather allows the lower parts of the engine case that are not part of the cylinder space where the action is to maintain a constant pressure. In operation the engine is pumping air and fuel into the cylinder burning it and forcing the exhaust gases out. The pressure in the cylinder is constantly changing. It is being controlled by action of the valves. So we get what we want which is the four stroke gasoline engine. Fine and dandy, most of the time.

While all this action is taking place in the cylinders the pistons are pumping air inside the engine case, but wait, that area is actually sealed. It is not easy, on a modern engine, for air to move in and out of the engine case. What happens is the air pressure inside the engine will increase. In the Old Days we ran a hose from the engine case to the outside air. Worked but it was messy. Exhaust gasses, blow by from the rings and noxious fumes were in the crank case. So the idea was to introduce these gasses to the intake manifold and have them burned in the engine. This is the modern engine PCV system and on our motorcycles we call it the engine breather.

When this system gets clogged or the valve defective the exhaust gasses increase in pressure and can blow engine oil past the rings and into the cylinder. That is why we think you should check the engine breather. It is very likely the source of your problem.

#2, I do not like the break in procedure you used for the new piston rings. You didn't say but do you remember, did you lube the cylinder walls and the piston rings with engine oil so they would not start up dry? (I'll warn you, this is a trick question)
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Old 01-01-2013, 06:04 AM   #18
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Here is a link to the Siebenrock cylinder kits (in english):
http://www.siebenrock.com/en/products/technic/

The kits sold by Motobins (at somewhat of a discount) are Siebenrock kits. It looks like the kits fit /6 and newer engine cases (i.e. not /5 without modifications). While a leakdown and compression test are good ideas - the final proof is in inspecting the cylinder bore.

Perhaps I am unique, but for me it takes about 45 minutes to get a head off my 1978 - but if you have not worked on many engines it would take longer. A new head gasket is all that is needed for reassembly provided the cylinder base is not disturbed. The Clymer and Haynes manuals describe the work in detail, but I found once the exhaust system is removed the job is very straight forward. Uniform loosening of the head bolts in steps is required. The left cylinder should be at BDC for inspecting the right bore, but otherwise it's not too tricky. Realistically, the total time is a few hours for removal, inspection, and reassembly. Take photo's along the way, keep everything clean, do not change the pushrods and valve train orientation, and remember anti-seize on exhaust nuts.

Does this bike have 200000 miles? If the mileage is ~ 50000 then it is unlikely new rings are needed. Also, only the right cylinder smokes - where the crankcase breather vents - is suspect since that is a path for oil. But all this is speculation. The leak, compression, and visual inspection will determine if the cylinder needs new rings. Good luck!

Stan_R80/7 screwed with this post 01-02-2013 at 07:14 AM Reason: Changed TDC to BDC (bottom dead center) - reword sentence
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Old 01-01-2013, 09:03 AM   #19
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Quote:
Originally Posted by motog View Post
......But, now I think about it, oil consumption has still been higher than it should have been all that time. The valves were broken in pretty carefully - low revs for the first 500 miles, then running it through the rev range thereafter. No odd noises, no piston slap, no obvious bottom end noises.......
This is I think the heart of the current problem. The rings are not seated. They need higher revs and they were improperly broken in. Most builders today do not oil the cylinders or the rings on a rebuild. The idea is to wear the rings into the cylinders fast. Thus they will be seated and they will seal.

The excessive blow by is being dumped thru the breather into the right cylinder.
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Old 01-01-2013, 09:03 PM   #20
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Disston: Thanks for that but the rings were not changed when the valves were done - so the rings should not need to be bedded in? is that correct?
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Old 01-01-2013, 09:34 PM   #21
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I don't know why but I thought you had new rings. If not then I was wrong.

So we are back at you need to do compression and leak down tests. You did say earlier that mileage was unknown? If not improperly seated rings then worn rings. Worn rings = too much blow by = oil dumped by breather into right cylinder.
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Old 01-01-2013, 11:26 PM   #22
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Yep, I'm pretty resigned to the fact that I'm probably going to have to do pistons, rings and cylinders. There's really only one way that oil can get into the combustion chamber - by getting past the rings. I'll still do the compression and leakdown tests but I'm pretty certain of what I'll find.

In the meantime I've been doing a bit of research and found this power-up kit for the R75/5 from Motoren Israel for about $860: http://www.motoren-israel.com/produc...mber-1975.html. Which is pretty tempting. The way I figure it, new pistons, a rebore etc will cost me about $650, but if I got the powerkit for only an extra $200, I'll get a new set of nikasil cylinders (that won't wear out in my lifetime), new pistons and a stinking great increase in power and torque. As an added benefit, I can do the change over in one afternoon, rather than having the bike off the road for 1-2 months (riding season is pretty well 12 months of the year here in Oz so this last point is important)

Does it sound like I'm trying to talk myself into this?

Has anyone else done this?
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Old 01-02-2013, 12:57 AM   #23
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Ok, so it only got the heads re-worked, nothing was done to the cylinders or pistons. Got it!

So - how many miles are on the cylinders and pistons?

Just because rings may be worn out doesn't necessarily mean pistons and cylinders are bad.

But if you want to talk yourself into new pistons and cylinders, don't let us stop you! I'm just saying there's a very good possibility all that's needed is rings. Just maybe, the ring gaps are aligned and all that's needed is properly orienting them! Cost = zero!

How many miles does it take to lose a quart?

I'd like to say that it makes no sense to me the breather could be causing this. For one, the breather dumps into the LEFT side on your bike. If it was dumping excess oil fumes into the engine, it would be the LEFT side that smokes, not the right!

Another interesting bit of data is that Oak considers the old style breather better than the new one and recommends replacing the disc when it goes bad with a new one cut from circuit board material. I don't know why he feels that way, but it is something to consider.
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Old 01-02-2013, 03:01 AM   #24
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How many miles on the pistons? No idea! I've had the bike for about 5 years and probably put about 10,000 miles on it. When I got it the original speedo was long since gone. From the condition of the lands on the rear drive (completely roached, they looked like shark teeth) I reckon it's done at least 100k miles. I have a vague recollection that the pistons had "B" marked on them which suggests they were already 1st oversize.

How many miles does it take to use a quart of oil? I haven't measured it because I've got in the habit of just topping it up every now and then. I wouldn't be surprised if it was using about a quart (that's about a litre i think) every 1000 miles- at least 2-3 times as much as it should. It has probably decreased a bit since I did the valves but not as much as I expected and it seems to have started to go back up again.

I hear what you say about worn rings not necessarily meaning worn barrels, so I reckon I'll do the tests and see how they look.

Wife is taking the kids to the beach for the weekend on Friday so I'm all clear to do a compression test, leak down test and top end tear down (if necessary) on Saturday. Just got to remember where I put the compression and leak down gauges. Probably should have done them when I bought the bike but the price was pretty good so I just wanted to get it out the door before he changed his mind.
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Old 01-02-2013, 06:48 AM   #25
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When you get it torn down you will be able to see how well the pistons fit. I thought mine were OK but they really weren't and when I ended up with new pistons it was what I really needed.

"B" on the cylinder is the mark for B cylinders, I think. There are A, B and C sizes. Then with in these three sizes there is 1st and 2nd over size. Do you remember what the number was stamped on the top of the piston? This number tells you much more than the letter B. I'm actually not sure a B on the piston is important. I thought the letter was on the cylinder.
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Old 01-02-2013, 08:44 AM   #26
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I think the letter is both on the piston and the cylinder, that's how they're matched up. the way I understand it, it's a way of working with the variable tolerances of production. Some come out bigger than others.
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Old 01-02-2013, 09:09 AM   #27
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Laugh Rings wear- replace

Rings wear check all tolerences and replace rings sounds like your problem. You had the heads done 2 years ago so you are good - now replace the piston rings and Connecting rod bearings while you have it apart and ride!!!

As stated in your original post power is good.
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Old 01-06-2013, 12:00 AM   #28
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I did the compression test today. Left cylinder 125psi. Right cylinder 127 psi (dry). Wet test (yes I know that you're not supposed to do wet tests on boxers but it's force of habit) right 145psi, left 155psi.
Haynes manual says 109-123 psi is poor 123-145 is normal and anything over 145 is good for R75/5. I had a short moment where I thought it was at the top of the normal range till I realised that R75/5 compression figures in the manual are higher than most other models.

Was going to do the leak down test but couldn't find my leakdown tester. Was thinking about pulling the heads off but then my mate (who's garage I was doing this in - I live in a 4th floor apartment) offered me a beer and it just went downhill from there.

So it looks like I'm only just above poor. Add that outcome to the blue smoke and I'd say that it's time for the top end to be stripped down and either new pistons, rings and rebore or one of the top end kits from Germany.
So I'll go back to my earlier question: does anyone have any experience of either boring out the cylinders on an R75/5 to fit early R80 pistons (which is about half the price of R75/5 pistons)? Alternatively does anyone have any experience of fitting the 1000cc power kits for the R75/5 from Siebenrock or Motoren-Israel?

I'm pretty tempted to just keep feeding it oil until summer and autumn are over and do the teardown in winter
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Old 01-16-2013, 10:48 PM   #29
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Any experiences of Siebenrock 1000cc kit for R75/5?

Now in the final throes of decision making. Got some ch coming in soon so need to make a call. Had almost pushed the button on buying the Siebenrock kit when someone in the local BMW club said that he'd seen three occasions that bigger cylinders had resulted in smashed crankshaft bearing housings. Admittedly this was putting BMW 900cc cylinders and pistons on a R75/5 rather than Siebenrock cylinder kits.

Does anyone have any verification of this?

Has anyone used the Siebenrock 1000cc kit on a R75/5?

Thanks
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Old 01-17-2013, 02:44 AM   #30
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The bottom ends of these bikes are pretty well the same whether or not you have a 600 or a 900, so I dont think that the extra power from the Seibenrock kit will be much of an issue, but do bear in mind that various components in the later /6 range were upgraded to take into account the extra power of the 900s. (I know that your bike is pre 900). I don't know for sure fitting bigger cylinders would result in smashed bearing housings, but I have never before heard that this was an issue.

Boring out 750 iron cylinders to 900cc was often done back in the day, but the results were often less than good with the thinner liner. Have you double checked that the Kit will fit the /5 without any crankcase modifications. Earlier power up kits did not fit /6 models unless some minor machining was carried out to the crankcase ( I think). You could check both issues with Motoren israel
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