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1973 R75/5 Re-commission
- Thread starter Russell94954
- Start date
Russell94954
New member
Sorry I should have been more specific. Once I took the rocker cover off the right hand side the exhaust valve gap was .035, I also ran a compression check and it came back as 0 on that cylinder. I am thinking exhaust valve is staying open by .025+ giving me the huge gap and no compression.
Does the valve rotate? The bike seems to have sat a long time. Could it just be stuck?
OM
Russell94954
New member
The valve actuates as expected with the rockers, I just think it's not fully seating, not tried to rotate, assume only way to check without disassembly is to try and rotate the valve spring retainer and see if the valve follows.
I just had a problem with a Kubota gasoline generator that I bought perhaps 35 years ago. It always started and ran great so I didn’t start it before I mounted it a the tongue of a trailer.
Once mounted, I pulled the starter cord and no compression. I determined it was a problem with the exhaust valve- being stuck. With a machine so old, I could barely find evidence of its existence searching the internet as the normal repair work be to pull the head but I would need at least a head gasket. With no parts availability. I gained access through the exhaust port and with penetrating fluid and my mig-welding pliers, I was able to free up the valve- good to go.
Good luck.
OM
Russell94954
New member
I hear you, same happened a couple of years ago with our lawn mower after it's winter hibernation, with that one a quick tap on the head of the valve freed it off nicely.
I will pull the exhaust and see what can be seen before committing to a head off job.
I will pull the exhaust and see what can be seen before committing to a head off job.
Be careful taking the exhaust finned nut off. If you've not had much experience doing that, it's easy for the threads on the head to gall. If you begin to turn the nut and it moves some and then stops, you're liking going to do some damage. Try some penetrating fluid like AeroKroil but the best bet is to cut off the nut and save the threads on the head.
Some exhaust nut advice-
forums.bmwmoa.org
OM
Exhaust Nut Wrench for 1971 R75/5?
Doing research for an upcoming retoration of my 1971 R75/5 and have found a number of special wrenches for removing the finned nut that holds the exhaust pipes to the heads. I anticipate some struggle getting a nearly 50 year old nut free so I think a special wrench would be valuable to prevent...
forums.bmwmoa.org
OM
Russell94954
New member
First time attempting to remove the nuts. I have some tri-flo soaking in there at the moment and will try a heat cycle tomorrow with a small blow torch and then keep soaking for a few days, I like the idea of trans fluid and acetone
I have no issue cutting them off if that is what is required.
All part of process.
I have no issue cutting them off if that is what is required.
All part of process.
Last edited:
stevenrankin
Well-known member
Sometimes, a tap on the wrench with a soft hammer or rubber hammer will start the nuts turning. I find this six times out of ten. St.
Russell94954
New member
Moving on from last weekend i decided to re-verify my findings from last time with regards to the potentially stuck valve. I performed another compression check in the same manner as before and it was apparent the stuck valve became unstuck pretty quickly, i am assuming the numerous cranking cycles last week worked to free it off. All was still not well with that same cylinder as i was still down on compression but i at least had some, i ran the test again with a squirt of oil in the cylinder and the compression increased substantially, still not close to the other side but a lot better. So sticky rings now....
I contemplated my next step and decided that trying to start the bike was the next move as this would not make matters any worse, but could unstick a stuck ring.
It had been a 5+ days so still with no fuel in sight i checked for oil pressure and was pleasantly surprised that it took no more than a few revolutions of the engine for the light to go out, great!, next was to install both petcocks in the tank which was easy enough, a splash of fuel with both valves off and no leaks, with both petcocks set to reserve i let both float bowls fill and then removed both bowls to check for consistent levels and both were fine.
The bike was wheeled outside, fire extinguisher at the ready and it was time...
After at least 25 years the engine started within 30 seconds with some tickling of the choke and throttle, plenty of sunflower seeds and what looked like wadding was spat out of one silencer and the other was clear, hardly any smoke to speak of, it sounded reasonably good, after a little while it wanted the choke off and it settled down to a pretty good idle, the one cylinder was definitely down on compression still but it was firing and firing consistently. I let it run for 5 mins and then called time.
I am very happy, this was always the initial goal, hear the engine running before really starting to get into the meat and potatoes of the re-commission, i.e commit more money and time.
As mentioned by someone previously i did find that i have leaking pushrod seals and the gasket between the engine casing and the cylinder so i might as well sort these out which will allow me to look at the rings.
Other tasks that will need attention are leaking fork seals, brake overhaul, i did find a stripped drain plug on the transmission so as i am pulling that it gives me the opportunity to replace the engines rear main seal and the o-ring for the oil pump cover to name a few..
I contemplated my next step and decided that trying to start the bike was the next move as this would not make matters any worse, but could unstick a stuck ring.
It had been a 5+ days so still with no fuel in sight i checked for oil pressure and was pleasantly surprised that it took no more than a few revolutions of the engine for the light to go out, great!, next was to install both petcocks in the tank which was easy enough, a splash of fuel with both valves off and no leaks, with both petcocks set to reserve i let both float bowls fill and then removed both bowls to check for consistent levels and both were fine.
The bike was wheeled outside, fire extinguisher at the ready and it was time...
After at least 25 years the engine started within 30 seconds with some tickling of the choke and throttle, plenty of sunflower seeds and what looked like wadding was spat out of one silencer and the other was clear, hardly any smoke to speak of, it sounded reasonably good, after a little while it wanted the choke off and it settled down to a pretty good idle, the one cylinder was definitely down on compression still but it was firing and firing consistently. I let it run for 5 mins and then called time.
I am very happy, this was always the initial goal, hear the engine running before really starting to get into the meat and potatoes of the re-commission, i.e commit more money and time.
As mentioned by someone previously i did find that i have leaking pushrod seals and the gasket between the engine casing and the cylinder so i might as well sort these out which will allow me to look at the rings.
Other tasks that will need attention are leaking fork seals, brake overhaul, i did find a stripped drain plug on the transmission so as i am pulling that it gives me the opportunity to replace the engines rear main seal and the o-ring for the oil pump cover to name a few..
gregfeeler
Dances With Sheep
The side covers started with the 1972 /5's. The tabs you see on the frame catch the back edge of the side covers but they are held in place by a large O-ring that attaches to a hook on the front inside of each side cover and stretches over the battery. It's a very flakey design as any failure of the O-ring will allow the right-side cover to immediately fall off. However, the left one is stopped from falling off by the left-side handle for hoisting the bike onto the center stand, so I'm doubtful about the "falling off in Idaho" explanation being the whole story, but maybe part of it.
stevenrankin
Well-known member
As a new owner of a BMW R75/7, I was surprised one day while riding to see my right cover sailing through the air into the grass on the side of the road.
The one O-ring broke. Since then I run two. There are various different fixes for this problem including drilling a small hole in the side cover and tie wrapping it to the frame.
I check those O-rings on a regular basis. St.
The one O-ring broke. Since then I run two. There are various different fixes for this problem including drilling a small hole in the side cover and tie wrapping it to the frame.
I check those O-rings on a regular basis. St.
Russell94954
New member
The side panels are so far down the list of "wants and needs" i'll probably circle back to looking for a set in the new year or beyond. I'm in no rush with the re-commission as it's more about the enjoyment of the journey.
Russell94954
New member
No real updates except that I was able to remove both exhaust nuts, not my finest hour but they are off and the threads on both heads are intact and look good which is the important thing, thank you to those whose said to bite the bullet and cut them off.
Both downpipes are toast, rotten from inside out so will add to the list of needs.
Hope to pull both cylinders this week(end) to see how everything looks.
Both downpipes are toast, rotten from inside out so will add to the list of needs.
Hope to pull both cylinders this week(end) to see how everything looks.
Russell94954
New member
It has been a couple of weeks with little progress due to other commitments, i was however able to remove both cylinders and both are dimensionally sound along with the pistons which is good news. The piston rings on the other hand not so good, although they look reasonable their end gaps when placed in the bore are far outside the .0118"-.01777" specifications (downloaded from the Brooke Reams website), i think one top ring end gap was .030". Also the thickness stated in the specifications tell me my top ring for a /5 should be .0705"-..0713", mine fall well within the specifications for the "All other models" which is .0680"-.0685".
I have checked the side clearances to they look good.
I have to assume the rings are original, that being said, have others found similar results when they have disassembled their engines?
Both cylinders are polished where the piston has been working so as new rings are in order i will need to get a hone and lightly hone the bores to allow for some cross hatching, i was thinking the stone hones are a little better for this as you can adjust the amount of pressure on the bore, if my thinking is not correct please by all means advise otherwise.
One other question if i may that whilst i am going to be ordering parts i'd like some help/direction please.
As the front section of my exhaust is rotten i was looking at the EME website and am surprised at the difference in cost between the pipes with a cross pipe and those without, is there really any benefit to having one with a cross pipe?
thank you!
I have checked the side clearances to they look good.
I have to assume the rings are original, that being said, have others found similar results when they have disassembled their engines?
Both cylinders are polished where the piston has been working so as new rings are in order i will need to get a hone and lightly hone the bores to allow for some cross hatching, i was thinking the stone hones are a little better for this as you can adjust the amount of pressure on the bore, if my thinking is not correct please by all means advise otherwise.
One other question if i may that whilst i am going to be ordering parts i'd like some help/direction please.
As the front section of my exhaust is rotten i was looking at the EME website and am surprised at the difference in cost between the pipes with a cross pipe and those without, is there really any benefit to having one with a cross pipe?
thank you!
kbasa
Well-known member
They’re hard to find, but BMW used to sell a little plastic grid that fit in the air inlet snorkel. It feels like a perfect 3d printing opportunity. The original just snapped into the opening.
Found one! $27.
