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ET: Engine (Twin) hard valve seats

timetraveller

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VOC Member
I wonder whether parts for either Merlin engines or cars are applicable? Our engines are air cooled, most are water cooled and in extremis the Merlins might even have used water injection. I think that there are others on here who know more about this than I do.
 

peter holmes

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VOC Member
Perhaps my Merlin engine example was ill chosen, but surely we have to look no further than Porche and VW, both running air-cooled engine for many years and miles, not now though. I would imagine they solved any problems with valve seat retention many years ago, probably when Vincents were still being manufactured.
 

roy the mechanic

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VOC Member
As it happens the R R merlin valve seats are screwed in using a four foot tommy bar. The throats are machined out afterwards. Apparently they are difficult to remove!
 

oexing

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VOC Member
A definite number of thou shrink fit cannot possibly correct as you have to take into account the size of valves and their rings. Same with bearings in alu cases, you have to calculate for each size the shrink diameter - or you end up with - don´t really want to write it, makes me vomit - staking the outer races seats !!!
Vincent valves are a bit close, exit and inlet, 43 and 46 mm, so yes, shrink fits for these seats are close as well and maybe only a thou different when doing the maths. As Merlin engines are mentioned here: BMW produced aero engines from 1917 and the great fuel-injected radials for the Focke-Wulf 190 fighter. So I guess they had sufficient expertise in the company to use in their motorcycle engines too. These classic bikes may have had some flaws but not in perfect fits for bearings or valve seats . So my numbers from the BMW manual are partly my bible - plus the great book by Ludwig Apfelbeck, once designer and engineer at BMW, Horex and others. I don´t look up "Tuning for speed" much, Apfelbeck is a lot more useful in the workshop really, not available in English I guess. So when using tool steel seat rings I´d stick to percentages of shrink fits like recommended in the BMW manual or at Apfelbeck´s and that would be around 7 thou / 0,20 mm or more.
This amount may be a bit less when you get modern rings like from the motor trade in my link. Top of page lists various types of material, below the recommended shrink fits. I have not had one of these yet, could be some sintered high expansion material. Look up the sizes in the files according to dimensions. So even with these alloys you find 5 thou shrink fit at Vincent sizes. So anything less would be too risky for me, I don´t want to end up with troubles like Ducatisti are used to, even more so with alu bronce rings.
Troubles can rise with too flimsy rings and alu heads with unsufficient amount of material around the seats. So do as you like at your own risk.
And no, 200 degrees C are no factor for alu heads for dropping in seat rings, another recommended number from the manual. Aero engines with alu heads run in the range 150 - 230 degrees , 170 continuous recommended. For Lycomings and Continentals 400 degrees F are best avoided, allright in the climb. But you can expect to exchange cylinder sets for cracked heads when hard used at these temps.

Vic
valve seat.JPG
 

litnman

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VOC Member
KTB notes RR 53C as casting alloy for cylinder heads. Also notes 'Y' alloy as an alternate. Were both alloys used and if so would this have any effect on valve seat
fitting?
 
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Vincent Brake

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@oexing
Why wouldn't one use Toolox 33
Tis temeperd at about 550 degree.
And heat expansion at 13 where 1.2379 is about 11.

Or would it drop as when used in exhaust, it softens and so shrinks to normal crystal structure??

Its not worrth the risk i guess.

But i try to order at rheinmetal.de
And to expansion test.
Maybe mr Neal V. has an empfehlung

Cheers.
 

oexing

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VOC Member
Heat expansion variations of 11 or 13 just account to minimally different sizes of rings I guess, not really relevant when looking at 0,20 mm shrink . Your tool steel was heat treated for use at 550 degrees, don´t think it will change dimensions in the engine. Plus the seat ring will not get much above 300 degrees in an alu head with great heat conduction.
My choice of 1. 2379 was from using it in the toolroom : At 12 % chrome it is a pig to machine, more so for reaming numerous bores as is typical in mould fabrication. It blunts reamers in short tiime - meaning it is very high wearing - or should I say low wearing ?? Confusing in English . A seat ring does not really need high hardness, some engine types got alu bronce rings or sort of cast iron types traditionally. While lead was used in fuels the lead prevented micro wear on the iron rings but today you need a different approach: That is why I went for the high chrome types and they don´t need to be 60 HRC as you want to machine the ring after dropping it in the head, so used in "soft" state. The chrome will provide a mini coat of well wearing protection so no lead is no problem. Of course you pick good valves as well with powder welded seat section. Don´t know about valves from the Spares Co so got mine from the motor trade like TRW , diesel valves my choice as sort of nimonic material, lightened.
I do not believe a ring will change its dimension by heat in use, this would have been known for many decades . When it really drops out it has more to do with uncorrect shrink fit and no substantional dimensions of ring or alu head recesses, not because of dimension changes from heat effects.
When having done heavy machining on components it is certainly a good idea to put them on an electric cooking plate at a few hundred degrees for a while to get stress lelieving before finishing to shrink sizes.
Did you look up my Ebay link, many seat rings easy for sale and correct material I´d think . Getting types from big companies may be awkward for small orders. Today I´d take that route , cheap enough and not a big operation on the lathe like with 2379 bars. "Hardened" seat rings is not quite correct, they have to be machineable , it is just a matter of wear resistance.

Vic
 
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Vincent Brake

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Ah yes i look up the ebay.

But i like to know what just i put in and why, call it autistic......

Thanx vic.
 

MartynG

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VOC Member
Heating the cylinder head is an issue as well........aluminium heated to 200 degrees Celsius will anneal the metal which turns it into expensive Plasticine.......... I think some of the earlier Godden heads suffered valve seat failures.
A few years back I had new seats fitted to my Comet's head. I understand only gentle heat was applied to the head but the seats were 'soaked' in liquid nitrogen for a time to shrink them before being installed.

Still in place, some 40,000 miles later
 

Vincent Brake

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VOC Member
I Used durabond 7 series now.

see other thread, i cant find it that quick to put a thread link here
 

Cyborg

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VOC Member
I Used durabond 7 series now.

see other thread, i cant find it that quick to put a thread link here
Durabond? Over here that’s cement board.

These folks sell valve seats as well, along with HD decompressors. Just don’t look at any of the tools, you may end up spending your children’s inheritance.

 

MartynG

Well Known and Active Website User
VOC Member
Durabond? Over here that’s cement board.

These folks sell valve seats as well, along with HD decompressors. Just don’t look at any of the tools, you may end up spending your children’s inheritance.

 

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