Valve seats

[tunnelrider]

Hi all,

I'm going down the road of valve seat replacement (need a couple of refreshments every now and then to take the sting out of it), my bike is a 1985 R65.

Does anyone know what the correct valve seat bore in the cylinder head is for the '81-on (40mm/36mm) valves? Is it 39mm, like the model before (ie with the 38mm/34mm valves)?

I've given mine to the shop already (can't measure now) and curious.

If anyone could give me the factory info on valve seats for the R65 '81-84 model (40/36mm valves), I'd be very grateful!  I've only got the factory info for 1978-82 R65 (38/34mm valves)


Cheers,
Dan

[Matt Chapter]

You seem to be asking for '81-'84 measurements, but you also indicate you have an '85.  The '85-'87 R65 motor is different than '84 and previous, although it fits in the frame the same.

If your chassis is a monoshock and you have the original motor, I would look for the '85 on specs.

[Kookaburra]

"The '85-'87 R65 motor is different than '84 and previous, although it fits in the frame the same."

Need to be very careful with model numbers, years and designations here. There is an overlap for most of 1985. The twin shock R65 was produced and plated up until September 1985. Mine for example is plated as 3/1985. Plugging your VIN number into the BMW electronic cattledog will generate the precise designation (and therefore specifications) for the motorcycle.  

[Tony Smith]

I don't think that there is much difference in the cylinder heads between an 84 and an 85 other than the rockers (which are such a good idea that BMW should have done 40 years beforehand that as and when a set become available I shall fit to my R65 and R100).

In any event the seats changed formulation several times so it is really only the most modern ones that you would fit.

And after all that, I've no idea what the bore size is, in any event it is largely irrelevant ans when after the machine shop digs out your old seats and welds the bores up, they will then set up a suitable interference fit with the new seats when they machine new holes to put them in.

Sorry if this is a stupid question and I've come in late, but why do you need new valve seats?

[tunnelrider]

Ah yes, the weird world of model designation!  Like Kookaburra, my twinshock R65 is plated (on the ADR certification plate next to the frame number on the lower right side) 5/85, which corresponds to the engine build date (top line stamped on milled area, lower left side of engine) week 20, '85, late April or May 1985.  Most of the twin shock model designations end at '84 and I don't recall seeing any literature on twin shock 1985.

I agree with Tony that the valve seat bores probably didn't change between '84 and '85 and yes you're right Tony it's largely irrelevant as they'll have to do what they do.  But as they'll be fitting their own seats it would be handy to know as a starting point.

The Clymer states 39mm for the seat bore for all R65, as does the '78-'82 R65/R45 BMW factory workshop manual.  I'm curious because the valve diameter changed (not sure when but it seems '81 on), and the intake at 40mm is then larger than the seat.

I'm going down this bumpy road because the old girl, at 171000km, has poor compression (80 kPa) and then one of the exhaust valve seats came loose, after lots of warning (which I was aware of but hey - it's summer right?).

Upon inspection, the other exhaust valve had receded into the seat so far it surely was not sealing compression properly.  This is apparently a problem esp for '81-'84 BMW's if using their full rev range, because of BMW's first attempt at valve seats for lead free petrol not conducting heat well to the heads.

[montmil]

Regarding valve seat replacement, here's an interesting video created by Ted Porter.

https://www.youtube.com/watch?v=R1rI3pog1DU

Link to Ted Porter's BeemerShop: https://www.beemershop.com/

The first cylinder head in the video had some serious valve seat issues. It belongs to our forum member Michael Crenshaw, aka: Bengt Phorqs. The bike is an R90 that came from an estate sale in Arkansas. So many things wrong. So much being made right.

As soon as the repaired heads are returned, Mike and I will also unpack and begin the install of a Siebenrock 1000cc top end kit. Attachment shows all the sweet goodies.

http://www.bmw2valve.com/motorcycle/B-2/1100085.html

I've been offered Shiner Bock and barbecue if I'll hold Mike's hand while we get this bike back making steam.

Yes, I'll take some snaps and post 'em. [smiley=camera_sm.jpg] I know the rules.

[Tony Smith]

 But as they'll be fitting their own seats it would be handy to know as a starting point.

Why? Correct seats available from Motobins and they are dirt cheap - it is the fitting that empties your wallet :-)

[tunnelrider]

Thanks for the link to the video Monte, Ted's got some good pointers there.

Motobins doesn't list valve seats for 40mm intake or 36mm exhaust valves, am I missing something there Tony?  Do you know if there is another size that I can use instead?

The shop hasn't started work on anything yet - I'm waiting for the valve kit.

I picked up a 1980 R65 engine yesterday - the heads are in better shape than mine.  After inspecting the barrel and piston, is there anything that should be done if I swap both my 1985 top ends for the 1980 ones?  Is this even a good idea?  I've got a top end gasket kit already.  I could possibly fit the new valve kit to the donor heads instead of repairing my one also....

Man aint life horrible with so many options, but I'm wary of emptying my wallet at a wrong machine shop. I'm reasonably confident the one I've found will be good - they only do motorbike heads and have done a couple of airheads before.  I guess if time and extra money wasn't a problem I could send them to someone like Ted, seems a bit OTT sending heads overseas tho.

Thanks for all your guys advice so far.

[Tony Smith]

Motobins doesn't list valve seats for 40mm intake or 36mm exhaust valves, am I missing something there Tony?  Do you know if there is another size that I can use instead?


They did list them, I'd be inclined to shoot them an email as they may have simply overlooked during a website update.

I picked up a 1980 R65 engine yesterday - the heads are in better shape than mine.  After inspecting the barrel and piston, is there anything that should be done if I swap both my 1985 top ends for the 1980 ones?  Is this even a good idea?  I've got a top end gasket kit already.  I could possibly fit the new valve kit to the donor heads instead of repairing my one also....

Ah, but the 1980 will have small valves - your kit will not fit. You would lose some HP and possibly have to fiddle with Carb jetting.


If the earlier engine is a small valve, then before using those heads drop at least the exhaust valves out and measure the wear (after first measuring the play in the guides). If they are anywhere near the wear limit I'd junk the valves given the less than stellar reputation the early R65s have for valve drops. Guides can be K-lined inexpensively.


Frankly you are probably better having your original heads done up - but for the reasons mentioned by Tom Porter - get the right seats yourself, even if you have to <gasp> buy genuine BMW. Without denigrating your machine shop of choice, the fact that they have already done some cylinder work on airheads may mean nothing more than that they have a fine set of mistakes they are ready to repeat.

[Tony Smith]

NZ has a quite active BMW community - find out who they use. If they use the people you are currently dealing with - fantastic, if not you will be pointed towards people who do know what they are doing.


I admit I am being pedantic. But when I took my heads to my local machine shop I wanted them to  simply use automotive guides and valves, they looked at my heads and refused to do so - which is why I ended up having to buy 1 over-sized guide at BMW's eye-watering price.

[tunnelrider]

when I took my heads to my local machine shop I wanted them to  simply use automotive guides and valves, they looked at my heads and refused to do so

Classic, was that a trick question to them Tony?  Great, thanks for your thoughts. There is a local BMW riders club here, I'll investigate.

[Tony Smith]

when I took my heads to my local machine shop I wanted them to  simply use automotive guides and valves, they looked at my heads and refused to do so

Classic, was that a trick question to them Tony?  Great, thanks for your thoughts. There is a local BMW riders club here, I'll investigate.

No it wasn't an intention trick question, in my own ignorance at the time I could see any reason why good cheap automotive parts couldn't be used. They patiently explained to me why it wasn't going to work and why it was better to buy the correct parts.

Not the first time Myers in Cairns have got me out of strife, they do quality work.

[peteremc]

Ahhh, Myers. Thought you had maybe taken your work to Myer, the department store at Cairns Central, Tony!

Until I googled and found the engine reconditioners. Hadn't heard of them previously, but will store that info in case I need them in the future.

Cheers

[Tony Smith]

Ahhh, Myers. Thought you had maybe taken your work to Myer, the department store at Cairns Central, Tony!

Until I googled and found the engine reconditioners. Hadn't heard of them previously, but will store that info in case I need them in the future.

Cheers

Absolutely 1st class workmanship, I used to use them extensively when i was on a mission to extract silly horsepower from VW engines, i used to get any work on motorcycles that i could not handle myself done by a friend in Townsville, but he has now retired and whilst he still does some work i prefer not to impose on him.