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Old 01-27-2010, 07:55 PM   #1
r2adv OP
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Airhead valve opinion

My son and I are almost down to the frame on our R90S project. Pulled the left jug off and I'm trying to decide what to do with the heads. Here are the before and after cleaning shots. Should the valves be replaced?

Before cleaning [img] http://ryanwerks.smugmug.com/gallery...74448637_PoduW [img]

After cleaning http://ryanwerks.smugmug.com/gallery...75102127_973Gw

I also noted the left side piston has an R stamped on top. Does is matter as long as I don't switch them?

Thanks

r2adv screwed with this post 01-27-2010 at 08:15 PM
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Old 01-27-2010, 08:01 PM   #2
Andy-Gadget
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Photo's didn't come out.
Put the first post address between the IMG brackets of the second post and Roberts your fathers brother


As to the heads, my suggestion is to fit unleaded seats, and new guides as a minimum.

One of the weaknesses of any "Older" boxer is the chance of a valve seat coming free, they come in three oversizes for this very reason.
The clasic situation for this happening is a thrash (the 90S was a "sports" bike for its era) up a hill, then stop, and enjoy the view.
When you go to restart the bike it won't turn over as the exhaust valve has fallen out of the head and is stopping the valve from closing fully.

New rockers is a good idea as the end that rubs on the valve stem wears out, causing large side loads on the guides, killing them as well.

Have fun
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Old 01-27-2010, 08:04 PM   #3
pommie john
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It's the other sides of the valves that are important. The face that seals onto the valve seat.

For the price of four valves, I'd change them and get the seats cut ( or replaced as has been suggested).
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Old 01-27-2010, 08:26 PM   #4
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Old 01-27-2010, 08:43 PM   #5
Andy-Gadget
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Do you have a valve spring compressor?

If so pull the valves apart, and with the valve in the guide, off the seat by about 5 mm, see how much side movement in the plane between the two valves.
Pay particular attention to the sideways movement possible as the valve seats, as this is what it is doing every time it seats, and isn't good if you want the valve head to stay attached to the stem.

BTW, BMW uses two piece exhaust valves, the stem is a different material to the head, the weld is about where the radius of the head blends into the parallel bit of the stem, on new valves you can see the heat affected zone.
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Old 01-27-2010, 09:19 PM   #6
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Truthfully?

How many miles do you have on the bike?

Unless the mileage is high, I wouldn't be as worried about the valve seats as AG is.

R-90's aren't particularly prone to have head problems and are also not known to need the seats replaced, unless it's due to high mileage. Some do, some don't and my R-90/6 is still running on the original seats after 150K+.

What I would do is find out where your best local BMW guy sends his heads and send yours there for freshening and new valves, springs, guides, seals, etc. Having the heads serviced is expensive but it needs to be done every so often. Don't forget... Those "S" heads are scarce and very expensive to replace. Take care of em!

The rockers? Have a pro look at the tips and check them for wear and end play. If you get a positive diagnosis, quit worrying. Mine were checked last month and they're shot. End play and bearings are fine but the tips are worn out. Oh well... One more reason to swap on an R-100 top end!
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Old 01-27-2010, 09:41 PM   #7
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As has been said, it's not possible to tell much without seeing the seats and the matching part of the valve.

From what I can see, they don't look bad - they're not sunken in at least, no pie shaped wedges missing, nothing major like that.

I have't heard of the seats falling out of the bmw heads. Perhaps over there in NZ or Australia where it gets pretty hot, a good hot run up a mountain may be over heating the heads a bit more than we'd see over here.

The unleaded seats thing didn't happen till 81 or so when BMW changed the seat material, so you don't need to worry about that.

Depending on the miles, if they're low, the guides aren't sloppy and the seats look ok, I wouldn't worry about doing a valve job. I'm a firm believer in not fixing it if it aint broke.
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Old 01-27-2010, 10:07 PM   #8
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Quote:
Originally Posted by Wirespokes
snip
The unleaded seats thing didn't happen till 81 or so when BMW changed the seat material, so you don't need to worry about that.

snip
What?
Unless you want to keep the valve lubrication industry going for ever then fit unleaded valve seats.
The old seat material, what is in the R90S, depended on the lubrication of the lead in the old fuel to prevent pocketing.
The post '84 valve seats don't need the lubrication, so can run unleaded without the addition of an additive.

So the R90S is a prime candidate for unleaded seats, the valves remain the same.
My '84 R100RS started to pocket its valves (monitor the clearance and all is revealed) when I stopped using lubricant (one way of finding out on an '84 model has unleaded seats fitted) as did my '84 R65LS.
1984 was the time that the factory change started to unleaded seats, so both bikes might have had the mod, but neither actually did, R65LS is now fixed, the R100RS awaits my extracting my digit, meanwhile I dose with lubricant, a PITA.
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Old 01-27-2010, 10:49 PM   #9
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Quote:
Originally Posted by Andy-Gadget
What?
Unless you want to keep the valve lubrication industry going for ever then fit unleaded valve seats.
The old seat material, what is in the R90S, depended on the lubrication of the lead in the old fuel to prevent pocketing.
The post '84 valve seats don't need the lubrication, so can run unleaded without the addition of an additive.

So the R90S is a prime candidate for unleaded seats, the valves remain the same.
My '84 R100RS started to pocket its valves (monitor the clearance and all is revealed) when I stopped using lubricant (one way of finding out on an '84 model has unleaded seats fitted) as did my '84 R65LS.
1984 was the time that the factory change started to unleaded seats, so both bikes might have had the mod, but neither actually did, R65LS is now fixed, the R100RS awaits my extracting my digit, meanwhile I dose with lubricant, a PITA.
As Terry said, BMW didn't have valve seat problems until 81, when they overcompensated for the lack of lead.
The pre 81 bikes are not an issue unless you see some serious problems when you dis assemble them.
Otherwise cut grind fix reassemble and ride it.
Robert
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Old 01-27-2010, 11:13 PM   #10
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Quote:
Originally Posted by Andy-Gadget
What?
Unless you want to keep the valve lubrication industry going for ever then fit unleaded valve seats.
The old seat material, what is in the R90S, depended on the lubrication of the lead in the old fuel to prevent pocketing.
The post '84 valve seats don't need the lubrication, so can run unleaded without the addition of an additive.

So the R90S is a prime candidate for unleaded seats, the valves remain the same.
My '84 R100RS started to pocket its valves (monitor the clearance and all is revealed) when I stopped using lubricant (one way of finding out on an '84 model has unleaded seats fitted) as did my '84 R65LS.
1984 was the time that the factory change started to unleaded seats, so both bikes might have had the mod, but neither actually did, R65LS is now fixed, the R100RS awaits my extracting my digit, meanwhile I dose with lubricant, a PITA.
Heres the thing...

The /6 bikes seem to work very well with the stock seats, even without lead and I cant say that anyone I've talked, to has experienced very many problems with the seats. Sorry, but that appears to be the way it goes over here. As Always, YMMV.

OTOH, the 80's era bikes are an entirely different story. There the problems are caused by seats that are too hard. When the seats are hard and theres no lubrication, you get valve recession. See how deeply the valve is sitting in this head?



The seat eats the valve's edge and you get a valve that looks like this, just before it fails catastrophically. That valve is sharp enough to shave with!:



And this is what the seat looks like: It's shot! This head is off of my 82RS and I think we caught it maybe 1000 miles before the valve got sucked in. I was most thankful because I was 4000 miles from home at the time and this would have been an expensive on-the-road adventure.



Lastly... Do you see anything wrong with this head? I didnt think so... It's the head that I recently removed from my 1976 R-90/6 and these seats have run well over 150K miles. They are still well within spec.



Heres the thing...

This issue with no lead and valve seats cropped up in the 80'swhen BMW got it wrong and installed overly hard seats but the earlier bikes seen to get by pretty well without needing conversions.

I aint gonna run out to the garage with a camera again tonight, so I'm outa here.
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Hawk Medicine screwed with this post 01-27-2010 at 11:27 PM
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Old 01-28-2010, 04:30 AM   #11
r2adv OP
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Valve rework?

My images aren't clear enough but the valves are not recessed into their seats. The bike has about 60K on it. Most other aspects of the engine look very good. I almost can't detect the spline wear on the trans. I expected to replace the rear main seal but everything was perfectly dry.

I think I'm going to hold off on any head work for now. Rebuilding the carbs, new starter and diode board, etc. are all eating my budget.
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Old 01-28-2010, 04:34 AM   #12
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Left or right pistons

I did notice an "R" stamped on top of the left side piston.

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Old 01-28-2010, 06:49 AM   #13
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The R isn't important (couldn't see it in the photo anyway) - just make sure the smaller valve pocket is facing forward.

After the troubles some of the guys have had with their rear main seals I'd be tempted to just leave it alone if it's not leaking.

Just a bit more data on the valve seat thing - it's not lubrication that was the problem but heat transfer. In anticipation of the move to unleaded, BMW engineers changed the seat alloy in 81. The new material didn't transfer heat as well which resulted in the exhaust valves eroding away. Exhaust valves are probably the hottest parts of an engine and drain their heat into the seats to cool off.

So it was only that period from 81 when the seat material was changed until about 84 when it was again changed to resolve the problem.
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Old 01-28-2010, 07:10 AM   #14
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Quote:
Originally Posted by Wirespokes
The R isn't important (couldn't see it in the photo anyway) - just make sure the smaller valve pocket is facing forward.

After the troubles some of the guys have had with their rear main seals I'd be tempted to just leave it alone if it's not leaking.

Just a bit more data on the valve seat thing - it's not lubrication that was the problem but heat transfer. In anticipation of the move to unleaded, BMW engineers changed the seat alloy in 81. The new material didn't transfer heat as well which resulted in the exhaust valves eroding away. Exhaust valves are probably the hottest parts of an engine and drain their heat into the seats to cool off.

So it was only that period from 81 when the seat material was changed until about 84 when it was again changed to resolve the problem.

Wire:

Thanks for that update. I own an 81 but the heads have been redone. I don't know what was done. Hmm.

I guess I still don't understand about valves all the way. I think I understand it all except for the valve seat. I always thought the part that the valve closed against was just part of the head. Apparently not. The valve seat is fastened to the head how? Press fit? Welded in? Hammered in? I'm missing some critical piece of information on how this works. Perhaps you can enlighten me.

Thanks,

Tom
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Old 01-28-2010, 07:59 AM   #15
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Quote:
Originally Posted by Infracaninophile
Wire:

Thanks for that update. I own an 81 but the heads have been redone. I don't know what was done. Hmm.

I guess I still don't understand about valves all the way. I think I understand it all except for the valve seat. I always thought the part that the valve closed against was just part of the head. Apparently not. The valve seat is fastened to the head how? Press fit? Welded in? Hammered in? I'm missing some critical piece of information on how this works. Perhaps you can enlighten me.

Thanks,

Tom
Any 1981-83 model that's got over about 50,000 miles on it almost certainly has had the valve seat issue dealt with.
Any model that's got less than that would require (not to suggest it isn't a good idea, no matter what, to have records) a service history to show that it's been done or not before anyone buys it.
My opinion on that whole unleaded gas thing is that it was, for the most part, bogus. During the switch to unleaded fuel, I was driving cars and riding motorcycles that were built in the 1960s and earlier. I didn't bother to do anything about the valve seats in any of them, and never saw a problem.
This includes a 1949 Dodge, a 1959 Royal Enfield Indian, a 1966 Royal Enfield Interceptor (my avatar), all of which I still have, and, purchased after the switch to unleaded, my 1965 R69S, and a BSA 441, neither of which required new valve seats when I restored them in 1995 and 96, and are still doing fine to this day. Well, ok, I holed the piston on the BSA a couple of years ago, and while I decided to replace the valve guides in the process of replacing the piston, the seats only needed a light clean-up.

The only situation where valve seat material might be an issue (based on my own experience with normal usage) is constant high-speed or high-load operation such as racing, or pulling heavy trailers.
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