Exhaust valve seat pocketing

John Roberts

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It's an R100RS, Sept '81. I ran out of Valvemaster about a couple of thousand miles ago and kept checking the valve clearance for the following thousand miles, all seemed well, no recession. I checked the clearance again yesterday and there was no clearance on one exhaust valve, I couldn't spin the pushrod at TDC when cold. I must have been just in time because there's no damage to either the valve or seat, the surfaces seem uniform all round the faces. Oh, when I say no damage to the seat, that's only half right, it's recessed about 20 thous, 0.020" or half a millimetre.

Given the date of manufacture, ie around the time BMW started to try various seat materials I can't say whether mine are to the new specs. but after 90,000 miles I'm thinking that 20 thous recession is quite reasonable and that there's no point in putting new seats in providing I start using Valvemaster again.

I must say that, once again, I am surprised at how little wear there seems to be on the engine, rocker faces, valve tips, pushrod ends, cylinder bores (ok, they are Nikasil) are like new, and there's less than .0004" wear on the vale stems. There's little side play on the valve heads so the guides seem fine too, but that's a matter of judgement of course. Good to see that every time I do some work on the engine I am struck by how well it looks inside. Oh, hang on, that's apart from the gearbox, that needs new bearings, we'll see how that looks when I open it up in a few days ... ;)

Anyway, back to my question: any point changing the valve seats, or just cut them back a touch to clear the step?
 
Unbleaded valve seats came on for the 1985 model year.. if you do decide to do the seats, replace exhaust valves and guides, valve heads can and do drop off for no particular reason, and at 90k miles you are in the danger zone.
(Some airheads will go mega miles without an issue, some drop their valves at 50k, seems to be dangerously random)


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You can identify unleaded seats if you take the valve out and clean up the inside of the seat. Hardened seats have two rings scribed around the inside. Old ones have one.

Of course if the seats are not OEM, then that won't apply.
 
Best engineering practice would say that at that sort of mileage, and given that signs of wear are now apparant, (and bearing in mind exhaust valve failure is not uncommon as previously mentioned) it would be very wise to replace the seats and exhaust valves and desisst using fuel additives which are of limited benefit nowadays anyway.

Spend the cash, it deserves it.........
 
My view would be to get them sorted so you don't have to worry. Send it to Mikeyboy to sort it.

Unless you like to play and fettle and bung in additives. I like to do little or no maintenance myself and ride a lot, but each to their own. :thumb2
 
My 77 R75/7 has the original seats and has been running on unleaded for 20 years, without any fuel additives
Valves havent needed adjusting in 40,000 km, and have gone 210,000 km.
I rarely rev past 5000 RPM------------.
Your seats will have been there for over thirty years , so if they will respond to a light clean up then do that and check them again in another 30 years.
If you need new valves best to get one piece ones and matching guides, and have them fitted by the supplier - either RM or a reputable cylinder head shop.
Messing around with old heads can be problematic, the alloy will have lost most of the original temper and be softer and weaker than when new , so the less you disturb the better.
Which is why K line inserts were developed to reline existing guides, and why some experienced guys dont like putting new seats into old heads unless there is absolutely no alternative.
 
Sorry, people, I'm still here and appreciate all your replies. I've been rather busy, and things have changed somewhat.

I managed to find a local garage who still had a set of valve seat cutters, he said I'd be welcome to borrow them and do the recutting myself and he didn't think the pocketing was too much of an issue and that the guides were fine, it was nice to hear him agree with my thoughts. Anyway, I did the job without much bother and then used the cutter with a sharper angle to relieve the port side of the seating face so as to reduce the width of the seating area to the recommended 80 to 90thou (0.080" to 0.090"). It cut OK to begin with then I realised the seat was turning in its recess. Curses.

I mentioned this to a mate who's into Austin Sevens, he reconditions gearboxes and engines, his name is Andy Bird in case anyone knows him- I know there are a couple of Austin 7 fans on here, Flipfly's late dad was one IIRC. He pointed out that there was a very good engine reconditioner twenty minutes away in Gaerwen on Anglesey. So I popped over and he said fine, no bother if I could supply the ten thou oversized inserts and new valves. So, gentlemen, my question now is: Who can supply such inserts, (my natural first port of call, Motor Works don't), so who does, please? I will carry on Googling of course, recommendations on here are usually good. :thumb2
 
The reason the seat is turning is because your head has lost its original temper and is soft and weak, as per my previous post.
So simply putting a new seat in carries the risk that it will just slacken off like the existing one.
Richie Moore has a fair bit experience with Airhead heads, and has his own source of valves and guides, and perhaps oversize seats too, so it might pay to contact him and see what he has, or what course of action he recommends.
 
I've just been quoted £275 for a pair of genuine BMW exhaust valves and oversize unleaded seats. I haven't been able to find genuine BMW valves elsewhere but Motorworks and Sherlock sell pattern ones for £43 approx each and I haven't found anybody other than a BMW dealer that sells seats, so I can't really compare the prices but it's a lot more than I expected. What do you reckon?
 
Have you tried motobins?
No, I hadn't, and Bingo! they have the exhaust valves (they say they are “100% original”) at £46.20 inc VAT each making them £92.40 for a pair, I haven’t got a price for seats, but even after allowing for the seats there’s quite a difference between £275 and £92. James Sherlock and Motorworks both sell pattern exhaust valves for a bit less (£42 and £44 approx) so the Moto-bins price seems reasonable.

In the past I have found some Airhead bits to be cheaper than the usual stalwarts- Sherlock's, MW and MB, it isn't that I go (much) out of my way to pinch pennies or even pounds, but in this case it seems to more than pennies. Unless I've got it completely wrong; it can happen! :augie

Thank you, Mike :beerjug:
 
Update.
Ordered from Moto-bins, £131 including delivery for 2 oversize exhaust valve seats/inserts plus 2 exhaust valves from the same manufacturer as makes them for BMW.
Thanks again everyone :beerjug:
 
That's a bit more like it:thumb
Spill the beans,,who quoted £270 odd:confused:

Mmm ... perhaps not. To be fair, the price was somewhere close to that quoted in the RealOEM site, and with that price difference I was wondering if they were priced in pairs, that might have made some sense. They bloody well weren't as it turned out. To be honest I have bought some stuff direct from this dealer that was cheaper than MW or Mbins in the past.

Oh, and Moto-bins wanted £22.80 each inc vat for the valve inserts. BMW Part No.11 12 2 325 741, Unleaded, 0.2mm oversize.
Exhaust valves were £46.20 each inc vat, 40mm "ALL 900cc & 1000cc (TO 06/1987) 45 DEGREE SEAT (STEM DIA=8mm)". BMW Part No. 11 34 1 257 837

Beatrice, the nice lady that answered the phone said I could have a 10% discount as I had ordered by phone rather than on-line. The total with carriage came to £131.
Result! :beerjug:
 
Good Result.

I'm not too far from the remote Motobins, so will pop into their shop as and when.

They price matched a pair of Continental tyres and Michelin tubes recently.

I was happy to give them the business instead of an on-line retailer, as I would prefer that they kept open for future business of supplying me and others with BMW airhead parts.
 
Beatrice, the nice lady that answered the phone said I could have a 10% discount as I had ordered by phone rather than on-line. The total with carriage came to £131.
Result! :beerjug:

Double check what you ordered is what you receive when it arrives!!!

She's the very reason I stopped using Bins after Steve left! Not once, but on 3 separate occasions!!

I've used Motorworks and Sherlocks (As long as Grumpy doesn;t answer the phone!) since then with good results
 


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