"The exhaust valve seats have been replaced to enable running on lead-free petrol,"...one of the most persistent myths in vintage automobiles and motorcycles.
Unfortunately, I appear to be one of those who still believe that valve seats can be a problem with unleaded fuel and older metallurgy.
The strange thing is that the worst case of valve and seat recession I have experienced wasn't on a particularly old bike. It is a 1984 BMW R80 that literally mushroomed the seats and valves after maybe 20,000 miles. I replaced the valves and haven't run the bike much since, but I always thought I needed to replace the seats as well. Of course I don't put that many miles on my old bikes, where as I did extended touring on the BMW.
I can help with basically one brand, since I have a rather narrow point of view on bikes
BSA Group had a policy of using hardened seats in alloy heads. For a BSA at least, when you spend MONEY with someone to remove hardened seats and replace them with hardened seats, what have you gained? Well, the risk of the seat coming loose
As for other brands, not sure what material they used for seats. From what I have read, Tr*&mph mostly followed the edict from Small Heath, but not always. But for the most part, Tr*&mph's don't seem to have seat issues either, so it must have been mostly.
only seat recession problem I have had in my T100 was when I took the head to the machine shop to have new valves matched to the seats and the bonehead created seat recession where there hadn't been any in 26,000 miles. In short, no recession on the seats from use. Cheers, Wilf.
Joined: Sep 2002 Posts: 7,811Alex
BritBike Forum member
BritBike Forum member
Joined: Sep 2002
Up until last year I have relied exclusively on vintage machinery for all my transportation needs for the last 25 years. All of these vehicles, I have performed cylinder head work on and all predate the removal of lead. They range from air cooled Volkswagens, Sunbeams, a Fiat, Hondas and BSA's. On top of that I have done head work on many more cars and bikes of every variety for others and not once have I seen this dreaded valve seat recession due to lead-free fuels. Now, I must admit my limited experience with iron heads where the seats are just cut into the stock cast iron (a '72 Triumph TR6 and an oldsmobile diesel are the only ones that come to mind), but I'm so convinced that no negative thing will come of it that I'm not putting any valve seats in my Silver Star motor.
As for the metallurgy? I'm no tribologist but I can't see how anyone can accurately predict the wear at the interface of valve and seat without some experimentation. And, for that, I have seen no data that would indicate that tetraethyl lead drastically reduces the wear of valve seats AND I have yet to find a circumstance where its absence drastically increases wear in any vehicle I've known or worked on. Hence, I come to the conclusion that in any circumstance that I am likely to encounter (I will maybe limit it to aluminum heads with cast in seats) these "lead free" conversions are at best misguided and at worst a hoax.
BTW, speaking of hoax. My Golden Flash had at one time received one of these lead free conversions, but what they had actually done was to cut out the cast iron that the seats were cut into and replace them with....wait for it....CAST IRON SEATS! Much to my chagrin, the cast iron seats started to fall apart and I had to replace them with nickel-chrome seats. So, I guess you could say I have a vendetta...
A smattering: '53 Gold Flash '67 Royal Star '71 Rickman Metisse '40 Silver Star '37 Rudge Special sixtyseventy Lightboltrocket road racer...and many more.
This is a 1964 A.65 Lightning Clubman, brought in to us for a full engine rebuild, with improvements incorporated.
, and as a small business person myself, at some point you either refuse the job or do it after you've said your bit against what the customer wants. And some customers just Know More than everybody. :> 'The customer is King'. And maybe you've heard the phrase 'well, do you want the work?' (my personal favorite :< ) I've talked my customers out of work the customer thought they wanted, but their trust is more important to me...
That people have perpetuated this idea as 'something that needs to be done' is maybe a bigger idea than shop owners want to fight, I can see the go along to get along side of the issue tho. Same problem for magazines accepting ads from advertisers that offer the service. Me, I'll save the money for something important and necessary, like beer or valve springs. Money, grrrr.
Interesting. The only time I have actually seen the valve recession problem is in the aforementioned BMW. Two BMW's actually, as a friend of mine had a similar year R100 with the same problem. And didn't the unleaded fuel thing start in the '70's?
I suppose that's how the "myth" gets started and it goes wild from there. I don't do much car work anymore, but I'm actually having a 1970 car motor rebuilt by a Britbike board member in Seattle who makes his living building old exotic car motors (and some motorcycles). Maybe I can get him to weigh in on this. I'll give it a shot.
I never saw any evidence of seat recession on my 74 Trident in over 50,000 miles of unleaded petrol. Although once I was lucky enough to get some leaded, 100 octane. The valves were very quiet.
Alex mentioned old VWs. Not really applicable, unless you do your own valve job. No shop grinds in VW valves. Generally you buy a rebuilt head, which includes new valve seats. Trust me, I've owned a ton of them.
Valve seat recession to the best of my knowledge has only been found in aero engines which is not supprising. They were tested extensively prior to the introduction of unleaded and the edict was, "Do not use unleaded under any circumstances in aircraft" As for cars & motorcycles I have seen some supposed "recession" but weather it was due to the fuel or some one being over enthusastic with the facing tool, no one knows and I run unleaded in an iron motor ( m20 ) with no recession problem. Ignition & plug problems a plenty but the valves have not needed adjustment for 6 years ( around 30,000 miles ), well OK, I could have, if I really wanted to but they are still just out of spec, inlet has grown & exhaust has closed up a little.
Note to Bodger, I work in a bicycle shop and a man drops off his wife's bike and says she will be in tomorrow to tell be what's wrong. In anticipation of her visit, I air up the tires, check out the derailleur, the crank, brakes and steering head and take it for a test ride. The bike is in really good shape. The lady comes in the next day and says her bike rides lousy. I said that the tires needed a little air but otherwise it was in good shape. She is not happy so I offer her $49.95 tune up...whcih checks the things I just mentioned and she is happy. The customer is always right even when they are wrong!
I have a 1980 R65 which went 70,000 miles till the valves started receeding. This is a common problem with the Factory BMW Valves from that time. So the valves got replaced with Black Diamond but the seats were just fine. The problem was the valves. My exhaust valves were sharp enough to shave by acording to Nathan Mendez at Boxerworks-Service. Original seats are still in the heads and the bike has just turned 100,000 mile yesterday morning.
So far I have seen nothing to indicate that the BSA suffers a similar problem. It seems the weak point is the valve guides. Those seem (?) to wear out sooner. So I'm looking for the right combination of Valve, Valve guide and tappet adjuster for the longest life of a head.
The Thunderbolt got black diamond valves and new guides without seals at 20,000 miles. I will probably put in hardened mushroom tappets if it looks like there is a benifit (longer valve guide life?).
two cents for your thoughts...
Gaggle of BSAs a Honda an old BMW and a Montesa Parking lot Elf in training