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If you're cutting your valve seats to 46* and your valve faces to 45* does it make any sense to lap the valves in as only a very thin outside edge of the valve will contact the seat with the head on the bench. After running the engine the 45* valve face should seat into the 46* seat alittle, shouldn't it?

A thin brushing of Prussian Blue would verify that the valve contacts the seat all around if you just tap it straight in and out a couple of times without turning the valve, right?

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Lapping is nothing more than polishing the machine marking out of the parts.

I'm on the fast lap side here. A couple quick spins with Dupont #7 is all I do. I think I mentioned this once before to polish the guides before running. The seats/valve faces get done as an incidental process.

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I like to mark the valve and seat with a black felt pen and then just a light dab of fine compound. I then lightly hand lap them and then check to see how everything is seating. I retired my valve seat grinders and use Neway cutters now.
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Unless, of course, you are using modern hardened valve seats. They are not going to pound in like the soft originals.

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Originally Posted by DMadigan
Unless, of course, you are using modern hardened valve seats. They are not going to pound in like the soft originals.


I think the 45 and 46 degree combination has only become common in modern times, with modern seats.


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I can say this forum is the first time I have heard of allowing different angles to "seat" into each other.

I can understand the potential advantage, but I'm not sure that I would want a seat or a valve that is soft enough to deform into its mate.

I have a rule of thumb... For street use one angle cut, and for track use three angle cut. The only advantage of a three angle cut is the flatter mating surface allows the system to take the beating of a stiffer/higher pre-loaded spring assembly without drawing in the valve.
In either case, one flaw, and the angle doesn't matter.

The only way to find/correct any flaws? Fast lap.

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I take it that this just applies to inlet valves, I was under the impression that exhaust valves needed a decent seating area to allow heat transfer away from the valve heads.

Last edited by gavin eisler; 07/26/15 2:11 pm.

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Originally Posted by gavin eisler
I take it that this just applies to inlet valves, I was under the impression that exhaust valves needed a decent seating area to allow heat transfer away from the valve heads.


+1



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Originally Posted by Zombie
I can say this forum is the first time I have heard of allowing different angles to "seat" into each other.

I can understand the potential advantage, but I'm not sure that I would want a seat or a valve that is soft enough to deform into its mate.



Britbike.com didn't invent it.

Look up "valve interference angle."


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Ok, I'm ready to cry "Snake Oil".

Quote:
Valve seats are often ground to the same angle as the valve face, but they can differ. The difference is called an interference angle. An interference angle allows for a quick bedding-in of the valve face to the seat on new engines. It may also allow for slight changes in angle as a valve heats and expands.
http://www.cdxetextbook.com/engines/comp/vlves/cylheadvlvseat.html

My opinion here is that IF you cut the seats to the same angle as the valves, and properly lap the join, you have a bedded in valve before the engine is even run. I do agree with leaving the valve slightly proud of the seat, perhaps 0.004-0.008" to allow for wear in a street engine.

I think this method (45/46%) is a way to cover up for soft components in a specific engine. The proper FIX would be to change the components.

"Slight changes in angle"??? Not going to happen. Unless you use silly putty for a seat, and Playdough for valves.

No dis-respect to anyone that follows this procedure but I can find several other measurable ways to improve the valve train.

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well..... it's been the recommended procedure on aircraft valves & seats for at least 70 years. I have manuals from the '40s to prove it. I used to build aircraft engines about 35 years ago & did a lot of cylinder work. it's the way we used to do it to eliminate the need to lap. also, if you look at an old school valve grinding machine you will see that it is marked at 44 and 45, 29 and 30. that being because you can also grind the valve up to 1 degree of interference. we used to grind the seats straight up at the major angle, and use 1/2 degree less on the valve... it's easier to do. so 29 1/2 on intakes and 44 1/2 on exhausts. you may not want to grind the new style valves if they are coated. also be aware that different manufactures reference the seat angle from the seat axis as well as the stem axis.

I have a vintage Sioux grinder for valves, but switched to Neway seat cutters about 10 years ago... way better than the old stones. the Neway valve cutter isn't too hot though. I've had two. it's light and portable, but not as good a job as a real valve grinder, so if you are thinking of buying one... look for a deal on an old grinder. if you want a Neway.. PM me, I'll make you a deal on the new style (no collets required)


and, as far as making a good fit... thats where the 3 angle thing comes in. you clean up the major angle on the seat, then test the fit the valve (new or re-ground). yes, the Magic marker makes a better record than Prussian blue. the top of the seat is narrowed to adjust the contact line by using a 15 degree cutter on 30 degree major angle seats (intakes). a 30 degree cutter is used over 45 degree seats. then the width of the seat is reduced by using a 45 on a 30 degree seat, and a 75 on a 45 degree seat. or you can use a 75 on both. this cuts away the inside edge of the seat without changing the contact line. if you're not racing, don't bother. bear in mind that those angels can vary with modern manufacturers. if you want to go 5 angle seats.... its just one more cut each on top and bottom to help smooth the gas flow

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That's all valuable info. Especially the aviation aspects. Those fellas research everything...
On another forum I am attempting to create a mathematical model of the creation of a black hole.
Mr. NickL, I believe you have provided the key I have been looking for... = 4/5 x Square-root Of Bugger-All.
This may stand right next to E=mc2 as one of the most profound realizations of all time. Of course I will credit the author, and share the Nobel Prize monies.

I can easily understand the premise behind the idea of mismatching the cuts, and I'm sure there are applications where this 45/46% method would apply but unless specifically instructed to do so in a particular application, I can't see trying it out.
I have had very few valve problems over the years, and none were ever caused by cutting or grinding issues. They always result from fuel mixture (heat), physical interference with the piston (broken springs/dropped retainers), or tulip-ing from excessive spring pressure.

The whole concept sounds interesting, no doubt there but I will have to give this tip a pass.
It just seems a "short cut" idea to me. Letting parts beat each other into fitting just sounds wrong.

Side note... I am a big fan of magic markers. I have bought one can of machinists blue in my life, and I wound up wearing 90% of that. I also find that Zinc Chromate spray primer makes a good register on aluminium.

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Quote
I think the 45 and 46 degree combination has only become common in modern times, with modern seats...

... I can say this forum is the first time I have heard of allowing different angles to "seat" into each other.

With respect for you fellows knowledge and experience, but - as Mitch says - it's not new.
First time I heard about it was in marine engineers school in 1967. Also 30 / 31 is used.
On ships where we had an on board machine shop, the angle diffence was applied during overhauls of propulsion and generator engines.
Valves are large and expensive so re-used after treatment in the lathe.

Seats were milled in situ, head on the work bench.
Lapping valve on seat with paste was limited to a minimum, and checked with pencil stripes.
Possibly it's a marine diesel engine or industrial diesel engine technique / aeroplane engine technique, that entered into automotive engines later.

The theory behind it is that the combustion pressure deforms the valve, so the 1-degree V-shape between the valve and the seat is reduced to zero.
This gives the exhaust valve the complete contact necessary to cool heat away into the seat.
If the angles are equal, the deformation will create a v-shaped opening which can be opened even further and allow burning gas to pass. The beginning of a failure.

I do not know about the aircraft engines Mitch mentioned, but an average marine engine runs 4000 hour per year.
MTBO (mean time between overhauls) of valves was in my days 1500 hours. Now - with better materials and seat cooling water systems - 6000.


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Originally Posted by me
I think the 45 and 46 degree combination has only become common in modern times, with modern seats.




Originally Posted by Mitch
well..... it's been the recommended procedure on aircraft valves & seats for at least 70 years.


Ok that's not very recent.

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Originally Posted by Zombie
Ok, I'm ready to cry "Snake Oil"........



.....I think this method (45/46%) is a way to cover up for soft components in a specific engine. The proper FIX would be to change the components.

"Slight changes in angle"??? Not going to happen. Unless you use silly putty for a seat, and Playdough for valves.


No material is totally rigid. Wouldn't surprise me if valve heads are measurably deformed by spring pressure and combustion pressure.

In fact they must be, or the labs and workshops wouldn't have come up with the interference angle!


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Quote
No material is totally rigid. Wouldn't surprise me if valve heads are measurably deformed

Completely true. And it's no snake oil, but basic engineering, applied physics and science.
All metal structures deform under load. The combustion pressure on valve seats is the largest force in that area.

In the UK the Ricardo Institute for Internal Combustion Engines did and does a lot of research on their own test engines
and do research and tests for their clients; engine builders who have a newly developped piece of an engine tested by Ricardo.
Clients vary from F-1 racing to long stroke slow speed marine propulsion.

Development engineers use 3-D computer models to watch the deformation and the gaps that occor and close in a method called finite elements.
Do a google search who is interested. The mathematics go too deep for me to hick up.

At my clients I've seen finite elements 3-D simulation in motion of a ships hull under stormy conditions. Largely exagurated but very illustrative and extremely frightening.
Do I have to sail the ocean on that elastic thing?
Bridge builders and tall building architects use the same techniques.

And less black box: Every marine engineer who sailed with large slow speed two stroke engines has seen the dancing ladies; cylinder heads of the main engine moving relativaly to eachother.
Not inches, but if one head rises 5 mm and it's neigbour drops 5 mm the 1 centimeter is very much visible.


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Not only does the seat area of the valve deform, but before this happens the head of the valve rolls around (wobbles) like a penny just before it come hard up against the seat.

If you are looking for a 50% increase, or approximately 60+ hp you will find most of it in the head. Some will be easy to find, but it will require a lot of work done by someone who knows these heads intimately. \Because of the REAL hemi-head design, the inlet, and exhaust port, being at such a low angle blocked from being raised by the vale spring pockets, one needs to be pretty clever to find USEABLE street hp/torque.

If the only thing on the table was taking a British 650 and getting a 50% increase in hp I would not start with a Triumph. It would be a lot easier with either a BSA and Norton. But each of these have their own issues that must be dealt with.


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rolls around (wobbles) like a penny

Would that be the result, John, of valve rotation?
We let exhaust valves of diesel engines rotate with a special rotating valve spring retainer, the "rotocap".
But I was told by people who know their trade that also without these rotocaps the valves slowly and intermitently rotate.


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My A65 valves show a definite fore and aft wear pattern on the valve stems, no rotation.


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Originally Posted by Ger B
Quote
rolls around (wobbles) like a penny

Would that be the result, John, of valve rotation?
We let exhaust valves of diesel engines rotate with a special rotating valve spring retainer, the "rotocap".
But I was told by people who know their trade that also without these rotocaps the valves slowly and intermitently rotate.



I'm happy to see you all giving such good input on this. It's easier for a fella like me to accept an idea if it is explained in details that follow a path of logic.

Now I do know that valves will rotate due mainly to seat deformations. The roiling penny analogy is a good one to visualize this.
Given enough time the seats, and valves will find a semi permanent position. Meaning the seats deformation becomes predictable/repeatable, and the valve will reshape to fall in line.

This still does not explain the differing angles or at least as well as Mr. GerB did. I have had tulip-ed valves, and I understand how they come to be. Even using the differing angles the life span may indeed be no better. Once the mating angles are gone... they're gone.
I see this as perhaps similar to my method of leaving the valve proud or raised slightly out of the seat. As time/wear progress my valve will settle into the correct installed height.
Perhaps there is a "Vee" on closing/compression.I am still ahead of the curve here.
The differing angle approach will seat the valve better in the beginning (theoretically) but will still lead to a sunken valve eventually.

This is one I would like to see side by side studies that show what actually happens with time.

My curiosity here is, IF this effect is real in all engines (or many engines) then why is this the first time I have heard of this technique? Why is this not common practice or at least why not a set of guidelines such as valve size/compression ratio/spring rates???

It's an interesting topic.

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Originally Posted by Zombie
why is this the first time I have heard of this technique?


I don't know.



Quote
Why is this not common practice [?]


Looks like it is.


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Originally Posted by triton thrasher
Originally Posted by Zombie
why is this the first time I have heard of this technique?


I don't know.






LOL... I knew that was coming.


Originally Posted by triton thrasher



Quote
Why is this not common practice [?]


Looks like it is.



I've asked a couple buddies that actively race (weekend drags), and neither of them have heard of this, and I just got back from a shop that does all the marine machining for this area, and he has heard this but recommends not using the method.

Without influencing him, his opinion was the same as mine. Why use a hammer to seat the valves when you can seat them properly with machine work.

I mean, I get it. I can understand the pro arguments. Maybe I can find something to try it on to see first hand. I have a bunch of QMB 139 engines that need work.

Are there guide lines that apply? Seat material/vale material? I have a piece of titanium bar stock that I can cut some seats from, and a pair of hardened steel valves for a 50cc 4 stroke.

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Never heard of Ti valve seats, but valves yes, Suzi gixxers and others use them, lightness is next to godliness.
i like the idea of the 45/46 and chamfered angles, why not , but not for exhausts, maybe new valve materials can take the heat, some one will know.


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I have the stock so I may as well use it.

The valves are hardened steel so the heat on the exhaust side shouldn't be an issue (for these small engines).

I don't know that the valve train is under enough load for the idea to be fair to attempt here but there is nothing to lose. I have 4-5 of these heads, and a couple of OEM, and aftermarket cams.
These are chain driven, overhead cam engines. 47mm/49cc They normally run 7-8k rpm max, and 3-5 Hp stock.
I run them with 50mm/90cc cylinders, shaved heads, and aftermarket cams to 10k rpm, and 8-9 Hp.

It'll be fun to try the interference fit valves to see what happens.

Here's the bike it's going in... 62mph 4t. (10 inch wheels...)

[Linked Image]


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excellent test machine. tell us how it goes with the new angles


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