R90s 1975

Post your post 1970 technical queries here

Moderator: Moderators

adrian967
Forum User
Posts: 77
Joined: Sun Mar 20, 2016 9:20 pm
Country of Residence: uk

R90s 1975

Postby adrian967 » Thu Jan 11, 2018 2:46 pm

Hi,
I have just had a valve guide overhaul from Roger Bennett and it needed it. The bike smoked badly and it was getting embarrassing. The piston rings are about a couple of years old and tolerances were checked by Siebenrock in Germany when i was over there.
I re- assembled the bike and now i get a whiff of smoke on the overrun, caught well in a picture coming into the carpark at Squires. I have the later edition reed valve and i am at loss what to do.
A) leave it and enjow the bike
B) barrels off and get Roger to check
C) change the engine breather
Oil tight by-the-way on the barrels
Thanks

User avatar
andyb
Forum User
Posts: 453
Joined: Fri Jul 12, 2013 9:40 am
Country of Residence: uk
Location: Notts, UK

Re: R90s 1975

Postby andyb » Thu Jan 11, 2018 8:53 pm

Assuming all valve work has been done correctly it only leaves the bores / rings. Maybe a good high speed thrash will help the rings bed in? The bore may be glazed.
Otherwise back to Roger to recheck
Andyb
R100R work-day-bike
Moto Guzzi V7 Stone fun-day-bike

User avatar
CharlieVictor
Forum User
Posts: 491
Joined: Tue Oct 18, 2016 6:22 pm
Country of Residence: France

Re: R90s 1975

Postby CharlieVictor » Fri Jan 12, 2018 5:56 pm

If the rings were the culprits, what could be the consequences of doing nothing (except unusual oil consumption and the associated billowing of smoke)?
1978 BMW R100S "Naked"
1999 W65L "Twin with a kick"

User avatar
andyb
Forum User
Posts: 453
Joined: Fri Jul 12, 2013 9:40 am
Country of Residence: uk
Location: Notts, UK

Re: R90s 1975

Postby andyb » Fri Jan 12, 2018 10:00 pm

Thats about it, a bit of burnt oil......assuming the bores are not massively oversize which could result in a ring breaking.
Seriously, a good thrash within the red line limits can sometimes work wonders! I think we all tend to ride our bikes too gently and sometimes that can produce problems.
One other thought - what oil are you using? 10/50 seems to burn less than 20/50
AndyB
R100R work-day-bike
Moto Guzzi V7 Stone fun-day-bike

John Marshall
Forum User
Posts: 779
Joined: Sat Jul 30, 2005 9:31 pm
Country of Residence: UK
Location: Exeter, the poor man's Swindon

Re: R90s 1975

Postby John Marshall » Fri Jan 12, 2018 10:27 pm

I had new guides and rings( one was broken) and I honed the bores.This on a 60/7.It smoked and sooted the plugs.Now all is very well. My 100RS burns some oil and probably could do with its guides doing,but it never smokes.
good luck John

User avatar
r90smick
Forum User
Posts: 11
Joined: Thu Jan 11, 2018 10:37 pm
Country of Residence: Ruislip,Middlesex UK
Location: Ruislip.Middlesex

Re: R90s 1975

Postby r90smick » Fri Jan 12, 2018 10:45 pm

Hi,At the time of replacing the piston rings I would have recommended honing the bores if the cross hatch honing bore impressions were not clearly visible.The cross hatch honing impressions retain the engine oil to lubricate the the cylinder liner and piston,if the bore is glazed the piston rings will push the engine oil into the combustion chamber which will then get burnt causing the exhaust to emit oil smoke.
I have experienced many a glazed bore whilst replacing piston rings on all airheads.
r90smick

ts
Forum User
Posts: 261
Joined: Sat Feb 16, 2008 3:01 pm
Location: Surrey

Re: R90s 1975

Postby ts » Sat Jan 13, 2018 12:06 am

Interesting. I'm curious wrt what the valve guide job included? Exhaust valve guides, or also intake guides? When the guides show significant wear it may sometimes be convenient to fit new exhaust valves as well, since the seats need recutting and the valves grinding in.

Smoking on the overrun is AFAIK due to oil being drawn down through the intake valve guides (with closed carb throttles) due to excessive guide stem to guide clearances, and may be confirmed by looking at the rear side of the valve heads from the intake port. Carbon/burnt oil will indicate oil having leaked past the guides, but this will obviously only happen if the bike is run hard enough for the intake valves to get hot.

Well, that's what I've been led to believe, please do correct me if I misunderstood!

How much oil have you seen in the intake elbows between the air filter box and the carbs, and in the carbs themselves (coming from the breather plumbing)?
ts
===========
'73 R75/5, '78 R80/7, '83 R80RT

adrian967
Forum User
Posts: 77
Joined: Sun Mar 20, 2016 9:20 pm
Country of Residence: uk

Re: R90s 1975

Postby adrian967 » Sat Jan 13, 2018 11:29 am

From what i saw of the reworked heads...new exhaust valves, new all 4 valve guides ( i presume a craftsman of his standing lapped them in )
When i took the heads in he removed the collets and springs you could easily feel the play in all 4 valves.

adrian967
Forum User
Posts: 77
Joined: Sun Mar 20, 2016 9:20 pm
Country of Residence: uk

Re: R90s 1975

Postby adrian967 » Sat Jan 13, 2018 11:40 am

Also, new valve springs/collets

adrian967
Forum User
Posts: 77
Joined: Sun Mar 20, 2016 9:20 pm
Country of Residence: uk

Re: R90s 1975

Postby adrian967 » Sat Jan 13, 2018 11:42 am

I must admit i have not done many miles (maybe 200) and not any speed since fitting the heads back on last summer.

User avatar
andyb
Forum User
Posts: 453
Joined: Fri Jul 12, 2013 9:40 am
Country of Residence: uk
Location: Notts, UK

Re: R90s 1975

Postby andyb » Sat Jan 13, 2018 12:15 pm

Your low mileage / how you run it will not effect oil burn through the valves. That will be determined by clearances between the valve shaft and guide. But some hard running may help reduce any oil leakage past the rings.

Just a thought, should the valve stems have been lightly oiled before the engine was first run after rebuild? If they were totally dry there may have been some initial wear.

There must be a little oil lost through the valve guides to keep the stems lubricated and this is determined by the valve shaft / guide clearances. Lapping valves in will only effect how they seal at the head and will not effect this clearance. So irrelevant whether the valves were lapped in or not (but I am sure they would have been).

Andyb
R100R work-day-bike
Moto Guzzi V7 Stone fun-day-bike

User avatar
CharlieVictor
Forum User
Posts: 491
Joined: Tue Oct 18, 2016 6:22 pm
Country of Residence: France

Re: R90s 1975

Postby CharlieVictor » Sat Jan 13, 2018 4:26 pm

Thats about it, a bit of burnt oil......assuming the bores are not massively oversize which could result in a ring breaking.
Seriously, a good thrash within the red line limits can sometimes work wonders! I think we all tend to ride our bikes too gently and sometimes that can produce problems.
One other thought - what oil are you using? 10/50 seems to burn less than 20/50
AndyB
Thanks Andy.
Interesting point about the "good thrash"
Actually the smoke on mine was very bad after rebuilt, and I did just that, progressively going though rev surges on 3rd and 4th gear. Never redlined it but getting close.
It did supress a lot of the smoke as the surges helped the rings bed in, but I never managed to completely get rid of it. Some days it she still smokes significantly on first start.
1978 BMW R100S "Naked"
1999 W65L "Twin with a kick"

User avatar
andyb
Forum User
Posts: 453
Joined: Fri Jul 12, 2013 9:40 am
Country of Residence: uk
Location: Notts, UK

Re: R90s 1975

Postby andyb » Sat Jan 13, 2018 9:36 pm

Smoke immedately after rebuild is a good sign, it means that the internals have been oiled. So I would not worry about that.

Smoke after parking......may indicate that some oil is blowing back into the air filter and hence to the carb inlets. And will run to the LH one if parked on the side stand.
Or again it indicates excessive wear in valves and guides.
Too high oil level can also give blow back problems.

I am in the process of fitting a deeper sump to my bike and will use a dip stick with a lower max on it - the idea is to increase the air volume above the oil to help stop oil blowing back.....alternatively I can run at the original oil level (with more capacity) for longer trips.....currently I have to top up about every 1500 miles.

If I had your bike i would personally do nothing until I had done a few more miles on it and had an indication of oil consumption. A bit of oil burn will not do any damage.

AndyB
R100R work-day-bike
Moto Guzzi V7 Stone fun-day-bike

adrian967
Forum User
Posts: 77
Joined: Sun Mar 20, 2016 9:20 pm
Country of Residence: uk

Re: R90s 1975

Postby adrian967 » Sun Jan 14, 2018 11:35 am

Thanks for all the suggestions...i will phone Roger fpr some reassurance. Had a rebore just a couple of years ago and they were checked last year at siebenrock. With the bike laid up i could take the barrels to Roger..but i dont really want to strip them off for nothing, laying on the garage floor days long gone

User avatar
CharlieVictor
Forum User
Posts: 491
Joined: Tue Oct 18, 2016 6:22 pm
Country of Residence: France

Re: R90s 1975

Postby CharlieVictor » Sun Jan 14, 2018 9:32 pm

Smoke immedately after rebuild is a good sign, it means that the internals have been oiled. So I would not worry about that.

Smoke after parking......may indicate that some oil is blowing back into the air filter and hence to the carb inlets. And will run to the LH one if parked on the side stand.
Or again it indicates excessive wear in valves and guides.
Too high oil level can also give blow back problems.

I am in the process of fitting a deeper sump to my bike and will use a dip stick with a lower max on it - the idea is to increase the air volume above the oil to help stop oil blowing back.....alternatively I can run at the original oil level (with more capacity) for longer trips.....currently I have to top up about every 1500 miles.

If I had your bike i would personally do nothing until I had done a few more miles on it and had an indication of oil consumption. A bit of oil burn will not do any damage.

AndyB
Again an interesting comment Andy =D>

The bike seems to burn a quarter of a liter per 1000 kms, which is acceptable and within BMW standards.
Yet when I top it up to closer to max, the smoke does increase. Smoking stops at some point, but the oil level is then close to min !!

In relation to your assertion, it makes me wonder if the dipstick gives a accurate reading. Maybe I am overfilling without knowing it? :-k

I'll check thoroughly at the next oil change.
1978 BMW R100S "Naked"
1999 W65L "Twin with a kick"

User avatar
andyb
Forum User
Posts: 453
Joined: Fri Jul 12, 2013 9:40 am
Country of Residence: uk
Location: Notts, UK

Re: R90s 1975

Postby andyb » Mon Jan 15, 2018 11:24 am

There was a good thread on here recently about the different oil sumps / dip stick lengths. Worth checking what your bike has.

With the larger (deeper) sump AND the lower pick up fitted the same volume of oil sits about 9mm lower with more air gap above. Which should reduce blow back and reduce crankcase internal pressures as the air will be compressible unlike the oil.

It surprised me that my R100R did not have a deep sump as standard but that was because they used GS parts for it and the GS sump was designed to carry a bash plate so the sump was not so deep.

Andyb
R100R work-day-bike
Moto Guzzi V7 Stone fun-day-bike

User avatar
bwprice100
Forum User
Posts: 1120
Joined: Wed Mar 11, 2009 9:49 am
Country of Residence: Wales
Location: Rhos, Pontardawe, Swansea
Contact:

Re: R90s 1975

Postby bwprice100 » Mon Jan 15, 2018 1:44 pm

You could try temporarily disconnecting the air breather pipe in the air filter box that refeeds oil back into the air input tract to see if the smoke is eliminated.

Brian

Sent by me using tapety talky

1958 R26, (not so many bits now)
1978 R75/7, (a project bike)
1981 R80, (was a TIC)
1995 R1100RT, (speeding ticket the first day I rode it) (Sold)
http://www.eBolt.co.uk
http://www.ToolroomChucks.co.uk

adrian967
Forum User
Posts: 77
Joined: Sun Mar 20, 2016 9:20 pm
Country of Residence: uk

Re: R90s 1975

Postby adrian967 » Mon Jan 15, 2018 9:18 pm

Thanks Brian...what if it does solve it? Breathing problem?
Adrian

User avatar
bwprice100
Forum User
Posts: 1120
Joined: Wed Mar 11, 2009 9:49 am
Country of Residence: Wales
Location: Rhos, Pontardawe, Swansea
Contact:

Re: RE: Re: R90s 1975

Postby bwprice100 » Mon Jan 15, 2018 9:21 pm

Thanks Brian...what if it does solve it? Breathing problem?
Adrian
You could check the condition of the breathe valve but you need to test it first.

Sent by me using tapety talky

1958 R26, (not so many bits now)
1978 R75/7, (a project bike)
1981 R80, (was a TIC)
1995 R1100RT, (speeding ticket the first day I rode it) (Sold)
http://www.eBolt.co.uk
http://www.ToolroomChucks.co.uk

adrian967
Forum User
Posts: 77
Joined: Sun Mar 20, 2016 9:20 pm
Country of Residence: uk

Re: R90s 1975

Postby adrian967 » Mon Jan 15, 2018 10:58 pm

The breather is the uprated type...replaced about 15yrs ago..do they fail?

User avatar
bwprice100
Forum User
Posts: 1120
Joined: Wed Mar 11, 2009 9:49 am
Country of Residence: Wales
Location: Rhos, Pontardawe, Swansea
Contact:

Re: R90s 1975

Postby bwprice100 » Tue Jan 16, 2018 11:52 am

Breather problems can be difficult to diagnose but at least the test I am proposing will confirm or eliminate it as an issue.
On the breather issue don't assume that because it is new it is working correctly.

Brian

Sent by me using tapety talky

1958 R26, (not so many bits now)
1978 R75/7, (a project bike)
1981 R80, (was a TIC)
1995 R1100RT, (speeding ticket the first day I rode it) (Sold)
http://www.eBolt.co.uk
http://www.ToolroomChucks.co.uk

adrian967
Forum User
Posts: 77
Joined: Sun Mar 20, 2016 9:20 pm
Country of Residence: uk

Re: R90s 1975

Postby adrian967 » Tue Jan 16, 2018 12:42 pm

Does orientation of the breather valve matter?


Return to “Airhead Q&A's”

Who is online

Users browsing this forum: No registered users and 6 guests