Seeking Bad Piston and or Cylinder Advice 1984 R80RT

[pollbmw]

Obligatory, "I'm sorry if this has been discussed before", if it has it didn't come up in my search of this site, snowbum, youtub, Google, etc.

The bike: 1984/83 R80RT, replaced speedometer, assume 100K-150K. I was given the old speedometer that had 85K? on it (lost) and the current one is at 35K. All done on the up and up as the old speedo was broken.
The problem: not as zippy as it used to be, verry difficult finding neutral at the stop (not seeing white smoke out of tail-pipe)
Test results
Compression test: left = 75psi , right = 90psi
Leak down test: left = loud hissing from oil reservoir, right = less load hissing from oil reservoir
Diagnosis: piston rings and/or cylinders are bad, and I won't know which combination until I pull the jugs off...

So I find myself in font of a rabbit hole. I plan on doing what I can myself, but I am no machinist. With that said here come my questions:

It's September, is it OK to keep driving it until the end of the season, or with those numbers am I on the cusp of something bad?

Once I pull the jugs I want to avoid playing games as much as possible, and with a number like 75psi I am assuming I need to re-bore. I live in Milwaukee, does anyone have recommendations for a machinist? How do I figure out what size rings/bore I need? Also, again with a number like 75psi, part of me wonders if I should just go big and get the Siebenrock 1000cc kit, which solves the problem by replacing everything that's leaking.

TLDR, both pistons & cylinders are failing compression, both at leaking into the oil reservoir. Left = 75psi Right = 90psi. Bike starts and runs with no problem, but need to open the throttle wide to get her to moving like she should. Should I stop riding her because she's about to blow up? With out pulling the jugs am I wrong to think I need to go straight to a re-bore or upgrade kit with numbers as low as they are?

Your knowledge and feedback would be greatly appreciated.

 

[stevenrankin]

So let us address the situation as I read. Low compression, oil use and failed leak down.

On your bike, you cannot rebore. You have nikasail lined cylinders. I say that but, only because I don't know of anyone who rebuilds nikasail cylinders. So, quite frankly, I would go with the Siebenrock upgrade kit to 1000cc. I say that as I may be doing the same thing myself this winter. It makes a lot of sense with no downside I can see. The cost of the kit is not all that bad as well.
Back in the day when I first rebuilt my 84 R80RT, kits like this did not exist and the cost of each cylinder minus piston and rings was around 2 grand apiece. So, I had a machine shop bore out the nikasail, install cast iron sleeves and went with new higher compression pistons and rings. That combination was far less money at the time and has lasted over 100,000 miles. I would do it again IF the Sibenrock kits didn't exist.

While you have the heads off, inspect the valves as well, early 80's bikes did have problems with valve seat recession due to a BMW failure. At 150K most likely you will need to have the heads redone as well regardless the issue of valve recession.

Once you Get the new jugs and pistons in with a new top end rebuild, you should be good for another 100K miles. Good luck, St.

 

[pollbmw]

So let us address the situation as I read. Low compression, oil use and failed leak down.

On your bike, you cannot rebore. You have nikasail lined cylinders. I say that but, only because I don't know of anyone who rebuilds nikasail cylinders. So, quite frankly, I would go with the Siebenrock upgrade kit to 1000cc. I say that as I may be doing the same thing myself this winter. It makes a lot of sense with no downside I can see. The cost of the kit is not all that bad as well.
Back in the day when I first rebuilt my 84 R80RT, kits like this did not exist and the cost of each cylinder minus piston and rings was around 2 grand apiece. So, I had a machine shop bore out the nikasail, install cast iron sleeves and went with new higher compression pistons and rings. That combination was far less money at the time and has lasted over 100,000 miles. I would do it again IF the Sibenrock kits didn't exist.

While you have the heads off, inspect the valves as well, early 80's bikes did have problems with valve seat recession due to a BMW failure. At 150K most likely you will need to have the heads redone as well regardless the issue of valve recession.

Once you Get the new jugs and pistons in with a new top end rebuild, you should be good for another 100K miles. Good luck, St.

Yeah, that's pretty much where my head is at. Also I should have mentioned my oil use is high, but I suppose that goes without saying given the compression numbers. Any issues riding it for another month or so before before doing the thing? Am I risking anything given my plan it replace the jugs and pistons this winter? Am I hurting the valves at all by holding off?

edited thread name to have model an year in title.

 

[omega man]

edited thread name to have model an year in title.

OM

 

[PGlaves]

There is a good possibility that the cylinders are just fine and the engine needs rings. Two things are equally true about Nikasil lined cylinders. One is that they can't be re-bored but the other is that they often don't need to be.

 

[pollbmw]

There is a good possibility that the cylinders are just fine and the engine needs rings. Two things are equally true about Nikasil lined cylinders. One is that they can't be re-bored but the other is that they often don't need to be.

My fear is I put new rings on and after spending time and money I have to spend more of the same. I played that game with my Vespa p200e until the only thing I hadn't replaced in the crank case were the bearing races. It's a long story and why I'm the only one I trust with my classic bikes...

 

[PGlaves]

My fear is I put new rings on and after spending time and money I have to spend more of the same. I played that game with my Vespa p200e until the only thing I hadn't replaced in the crank case were the bearing races. It's a long story and why I'm the only one I trust with my classic bikes...

Of course. So a careful examination and measuring of the cylinders is in order before deciding whether new cylinders are needed, or not.

 

[stevenrankin]

Back when my original nikasail jugs went bad it turned out the pistons had been slapping the jugs and deformed the cylinders beyond just needing rings. So as Paul says, measure carefully and determine the bore is cylindrical and not pear shaped or any other shape it should not be.
Still, I like the idea of the big bore kit. St.

 

[oldcamper]

+1 on keeping the nikasil cylinders AND the 800cc displacement.
IMHO, 750-800cc is the optimal displacement for an airhead. They run smoother and the smaller exhaust valves last longer. Input splines on the transmission seem to last longer too, maybe in part due to shorter gearing and lower power pulses. The difficulty finding neutral might indicate a dry/worn spline problem, BTW.

75-90 psi compression seems very low, even with worn rings. Are you sure valve clearance is correct and was the test run on a warm engine with the throttle wide open? The nikasil airhead engines are generally not known for worn rings but they are well known for exhaust valve issues. I’d look there first.

This machine is 40 years old after all. I have no idea of its cosmetic condition but if the rest of the bike is tired you may be better off simply purchasing a lower mileage example if you intend to put many miles on it. Personally, I don’t think a 1000cc Seibenrock kit is likely to add anything to the value of the bike. It’s usually better to keep the old airheads stock.

There is an active local BMW club in your Milwaukee area. Their annual rally was just this past weekend at the Dells. You might consider attending a meeting to learn of local resources and obtain additional advice.

 

[melville]

+1 on keeping the nikasil cylinders AND the 800cc displacement.
IMHO, 750-800cc is the optimal displacement for an airhead. They run smoother and the smaller exhaust valves last longer. Input splines on the transmission seem to last longer too, maybe in part due to shorter gearing and lower power pulses. The difficulty finding neutral might indicate a dry/worn spline problem, BTW.

75-90 psi compression seems very low, even with worn rings. Are you sure valve clearance is correct and was the test run on a warm engine with the throttle wide open? The nikasil airhead engines are generally not known for worn rings but they are well known for exhaust valve issues. I’d look there first.

What he says--my R75 runs so much sweeter than my R100 but I do like the power with a pillion in the mountains.

With the CV carbs a compression test is best done with the carburetors removed. I've been happy with how a bike was performing at about 120 psi cranking but when the heads came off to deal with a stripped plug hole a hone and fresh rings got it up to 140 psi after a short break-in period. A true 75 to 90 psi is probably reaching the end but I would enjoy the rest of your riding season and make it a winter project.

 

[kbasa]

Given that it's an 84, you might in the end stages of valve recession, so I'd start there. Have you had to do valve adjustments more frequently? Are the intake and exhaust screw adjusters majorly different from each other, with the exhaust having lots of extra threads on the outside of the locknut? When you do a valve adjustment, do you have to always adjust the exhaust, but never the intake or at least not to the same degree as the exhaust?

I've had an 83 and 84 R100 and they both needed the heads done due to valve recession at about 50K miles.

That's where I'd go second. I'd start with a leak down test and do some listening to where it's leaking then proceed from there.

Good luck. If it's all hosed up, then Siebenrock is gonna be your friend.

 

[pollbmw]

Given that it's an 84, you might in the end stages of valve recession, so I'd start there. Have you had to do valve adjustments more frequently? Are the intake and exhaust screw adjusters majorly different from each other, with the exhaust having lots of extra threads on the outside of the locknut? When you do a valve adjustment, do you have to always adjust the exhaust, but never the intake or at least not to the same degree as the exhaust?

I've had an 83 and 84 R100 and they both needed the heads done due to valve recession at about 50K miles.

That's where I'd go second. I'd start with a leak down test and do some listening to where it's leaking then proceed from there.

Good luck. If it's all hosed up, then Siebenrock is gonna be your friend.

I only put about 1K worth of miles on it in a given year, so I did not check the valves this year, mainly because I already knew there were some compression problems from last year. My go forward plan is to put the spark plugs back in and enjoy it until I'm ready to put her up for the season. Once I do that I'll take a closer look at the valves, piston, and cylinder. I appreciate everyone's feedback on this!

 

[mark_bartels]

Millennium Technologies | Nikasil Cylinder Plating

Specializing in Nikasil cylinder plating, cylinder boring and cylinder repair. Cylinder head porting and repair. Crankshaft repair and crankshaft balancing.

millennium-technologies.com

 

[pollbmw]

Head smacking update. This is usually my weekend ride because I need to drive a van to do my business. Well, my van was in the shop, so I decided to take the bike to work and do what business I could. So I get home after driving her all day long and run a compression test. 125 psi, both side. So while I'm feeling kind of stupid right now, I'm pretty happy that I'm going to save me some money...

Now I need to do the same thing, then fiddle with the clutch to make sure that's all good.

 

[20774]

Sounds like some good news!!

 

[stevenrankin]

Well that is some good news, enjoy the riding. St.

 

[oldcamper]

Now I need to do the same thing, then fiddle with the clutch to make sure that's all good.

Clutch splines on those bikes need to be lubed occasionally. The process involves moving the transmission back a bit to access the splines.

It’s not difficult but you should read up on how to do this properly before unbolting stuff.

 

[pollbmw]

Clutch splines on those bikes need to be lubed occasionally. The process involves moving the transmission back a bit to access the splines.

It’s not difficult but you should read up on how to do this properly before unbolting stuff.

I have done this within the last few years.