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Exhaust valves #788117 10/25/19 8:25 am
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Arnstein Offline OP
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https://1drv.ms/u/s!AsKcYdC1qRK7jj3QdDhsXJh1lwsm?e=S4vrYl

The Quality of the exhaust valves that can be bought these days (and for many years), has a very low wear resistance, in my experience anyway. All are made in stainless and some are even called diamond (must be the softest diamond ever). I have been doing a lot of miles through the years on my BSA, this last summer 10500km ( ca 6500 miles) and every time I service the cyl.head ( ca 30 000km) there will be badly pitted ex valves.
The valve to the left in the picture is one example of such pitting. Valve nr.2 has had a groove grinded and hard wearing bronze welded on (5 - 600 Brinell), valve nr.3 the bronze seat is grinded and ready for use.

I have done similar many years and ca 30 000 km ago in my old H...a and the wear of these valves are almost none. When also having hard type seats in the cyl.head the lifetime of valve and seats will be very much longer. The same type of bronze can also be welded on camfollowers, the wear resistance being excellent.

The LH picture is from the H...a workshop manual showing stellite welded on, which seems to be H...a practice.


Arnstein

BSA Spitfire MK3.800cc (also engine 850cc 90degree)
Honda CB450T -71
Laverda RGS 1130cc -85
Ducati 1098 -08
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Re: Exhaust valves [Re: Arnstein] #788125 10/25/19 10:46 am
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gavin eisler Online Content
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Interesting, i noted something similar last time I inspected the valves, about 10 percent of the damage you show, only after about 3k miles, at the time i put it down to the failure of the epoxy inlet filler.
Your guides must be good quality if its worth the bother to reface the valves, I take it that the stems are showing little wear?


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Re: Exhaust valves [Re: Arnstein] #788130 10/25/19 11:39 am
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Arnstein Offline OP
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The guides in this my "spare" engine 800 cc is ok and the wear on the stems is only 0.01 - 0.02mm. If buying new valves I will weld on this hard bronze (Castolin 9000) before installing. I have not had this type of bronze rod for some years, but finally ordered some. So from now, no more pitted valves.


Arnstein

BSA Spitfire MK3.800cc (also engine 850cc 90degree)
Honda CB450T -71
Laverda RGS 1130cc -85
Ducati 1098 -08
Re: Exhaust valves [Re: Arnstein] #788203 10/26/19 3:35 am
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NickL Offline
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Have you tried lash-caps or/and mushroom headed tappet pins?

Re: Exhaust valves [Re: Arnstein] #788225 10/26/19 9:37 am
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Arnstein Offline OP
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https://1drv.ms/u/s!AsKcYdC1qRK7jGddd4NOcS04rPxm?e=Wre1GS

I have used the elephant foot type (picture) in resent years and also mushrooms for many years, so it´s not that end getting pitted anymore, it is, as said, the too soft seat on the other end on exhaust valves that\s getting pitted. On the inlet I have the original cast iron seats and the SRM big valves which works verywell.. of course being cooler and also getting a little lubricated by the incoming gas.


Arnstein

BSA Spitfire MK3.800cc (also engine 850cc 90degree)
Honda CB450T -71
Laverda RGS 1130cc -85
Ducati 1098 -08
Re: Exhaust valves [Re: Arnstein] #788289 10/27/19 1:16 am
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NickL Offline
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Ahh.... sorry i should read and look first..

That pitting does seem excessive, i guess it's the lack of lead in fuel now.
I used to suffer exhaust side overheating in long races but not that pitting you are getting.
Cured by using albronze seats and slightly heavier valves plus ducting more air.
Sellite tips on valves used to be standard practice but i've not seen it used on the faces before.

I notice that SRM are selling a 'plasma hardened' valve now. Maybe to address this.

As you say the inlet side runs much cooler so is seldom a problem.
Nice job on the welding/refacing an excellent solution.

Re: Exhaust valves [Re: Arnstein] #788316 10/27/19 9:24 am
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triton thrasher Online Content
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[Linked Image from i.imgur.com] https://i.imgur.com/jgTwVQ6_d.jpg?maxwidth=640&shape=thumb&fidelity=medium

The valve on the left is showing the pitting that you get when carbon sticks to the seating faces.

On my bike it was mainly rich mixture that caused it. For all I know, burning oil could do it too.


Amateur Loctite enthusiast.
Re: Exhaust valves [Re: triton thrasher] #788321 10/27/19 10:25 am
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Arnstein Offline OP
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When having hardened seats on both valve and in cyl.head this pitting is almost none even after high mileage. I think rich mixture / burning oil affect pitting, but not by much compared to the stainless soft valves that´s sold. I have tried finding better valves without luck, all are similar with soft seats and upper end. I think SRM many years ago sold some with chromed stems and maybe welded on hardening.


Arnstein

BSA Spitfire MK3.800cc (also engine 850cc 90degree)
Honda CB450T -71
Laverda RGS 1130cc -85
Ducati 1098 -08

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