Burning oil, what do I replace?

[DeeG]

OK, guys and gals, before I send a bunch of money to England, I need to run something by.

The 45 is burning oil, about 1.5 qts per ~600 miles. Highway speeds, 85F+ temps.  

I was planning on purchasing valves, rings and associated miscellany.  I don't need to buy new pistons too, right?  I've never done this kind of thing before, and I feel kinda stupid not knowing exactly what i need.  If I need them, I'll get them, but I'd rather not spend the $$ if I don't have too.

   Thanks,

Dee

[Semper Gumby]

You need to measure the bores and the pistons to see if you need those.  There is a maximum clearence for these two measurements.  

In the past I've gotten away with a dingleberry hone and a new set of rings.  At 107,000 miles I still have the original pistons on the 1980 R65.  

I had a knock at idle that went away at speed. Turned out my small end bushings were oblong.  All this and the valves were  done about 65,000 miles.

Curious: What compression have you got?  Do you see smoke under acceleration or when you close the throttle?

Good luck.

[Rob Valdez 79 R65]

Yes Dee, a compression check, done correctly; and a leak-down test are mandatory before spending money on parts.

Then there is the test for cylinder out-of-roundness.  This is done with a dial bore gauge.

Mind you, I've never performed any of these tests myself, I just know about them from reading.

It could be that your valve guides need replacing.  Bob Grauer (408 248 9732) in the SF Bay area is my man for head work.  If you hire out any work you need to MAKE SURE they are experienced in airheads.

Another thing to check is the cylinder walls.  They may just need de-glazing, which is what the honing tool that Bill mentioned can be used for.  New rings would probably be in order if you do this.

How many kilometers/miles on the bike?

[Bob_Roller]

Probably not an issue, but a quick check of the crankcase breather valve to see if it is still intact and working properly.

  If it isn't, you may be losing oil out into the airbox, a little oil in there is normal .

[montmil]

Mileage?  With this vital information, a better diagnosis may be formed.

Airheads are notoriously long-lived engines. I bet on the simple; maybe valve guides.

Compression test first, by all means. There's a bit of gear required for the leak down exam but most bike shops and perhaps a local auto repair friend could perform this.

Whatcha got for us, Dee? Many doctors are in the house. Too early to start spending money.

[DeeG]

There are roughly 38,000km's on the odo. It smokes a bit on startup and idle, but give it throttle and it likens to a diesel p/u truck.  When we were heading back from the National last year, Pete said it got kinda nauseating riding behind me......

I got a compression tester for Valentines Day last year, so I guess its time to drag it out and learn how to use it.  

It smokes worse on the left side, not sure if that makes a difference.

[Rob Valdez 79 R65]

It smokes worse on the left side, not sure if that makes a difference.

You are not using the sidestand as a regular prop, are you?
These engines like to be on the centerstand when parked for more than an hour or so.

[Justin B.]

You didn't mention the year but 81 and later have the Nika-Sil cylinders so it's not likely you will need new pistons and these things just laugh at a hone.  The Dawg used to kill every skeeter in sight after warming up and I found the oil ring end-gap almost three times normal - a fresh set of rings later and it uses absolutely no oil.  Unlikely valve guides will cause much of an oil burning issue since the oil is always flowing away from them.

[Rob Valdez 79 R65]

Look at her sig line, Justin.  All of her airheads are pre-Nikasil.  In this case, I am comfortable in assuming she is talking about her R45.

Measuring ring gap - do you remove the rings from the piston and insert them into the cylinder one at a time, and measure the gap with feeler gauges?

Thank god for Google!
From: http://www-cdr.stanford.edu/~petrie/bmw/R80ST/engines.html
(this is from the next-to-the-last section on the page)

Piston rings
 Â Top:
 Â   Type                       Plain, rectangular section
 Â   Thickness:
 Â     R45                      1.478-1.490mm (0.582-0.0587")
 Â   End gap - installed:
 Â     R45                      0.25-0.45mm (0.0098-0.0177")

Second:
 Â   Type                       Plain, with stepped or tapered face
 Â   Thickness
 Â      /7, R45 up to '80        2.010-2.022mm (0.0791-0.0796")
 Â   End gap - installed:
 Â     R45                      0.25-0.45mm (0.0098-0.0177")

Oil scraper:
 Â   Type                       One piece
 Â   Thickness
 Â      R45 up to '80            3.510-3.522mm (0.1382-0.1387")
 Â   End gap - installed:
 Â      R45                      0.25-0.45mm (0.0098-0.0177")


Dee, you will still want to find someone with a dial-indicator-gauge that can measure the bores for you for out-of-roundness.

It seems that same spec sheet is also on Duane Ausherman's site (I saw his link at the bottom of the first page... http://w6rec.com/duane/bmw/engine.htm )

[tvrla]

At 35K I can't imagine rings being needed. The valves and guides should be fine too.

It's possible the bike was babied and the top rings are stuck from carbon buildup.

These bikes are so easy to work on, why not take an hour or two, pull the cylinders and take a look? Clean off any carbon buildup, post us some pictures, take the heads to someone knowledgeable and go from there. Using that much oil, the bike shouldn't be ridden anyway.

But--- before going to all that trouble - the first thing I would do is check the breather feed-back hole. If it gets plugged, it can cause problems like you've got. It's the first thing I'd check. It's a very small hole one mm diameter and if it gets plugged, oil that's blown out the breather won't be able to return to the crankcase, and will be channeled to the carburetors to be burned instead.

[Semper Gumby]

Well at 29k I needed rings in my 1980 from the DPO not taking good care of the bike.  That brought the compression back up from 110 and 115.  

When Nathan at Boxerworks did the heads at about 65,000 miles, he put another set of rings in.  So I have had two set of rings on the original bores and pistons.  Now 107,000 miles and counting...

[DeeG]

Thanks guys,

I will probably not have a chance to take a look at the bike until next month.  And in the mean time, I hope the British stay solvent until I figure out what I need to buy.....      

And no Rob, the bike might spend 20 minutes at most on the sidestand.  Pretty sure the previous owner also kept it on the center stand.  Before it was shipped to the States?  who knows...

I'll call up one of my airplane mechanic friends.  Perhaps I can get one of them to come by with his bag o tools and help me out.