Re-angled big valves

jseng1 · Jan 20, 2018

New photos re-angled big valves showing the alignment of the valve tip with the rocker. These now photos have been added to the end of the (edited and reloaded) video below. Rocker tip alignment doesn’t always come out well when using a mill – sometimes great and sometimes so bad that you need mushroom adjusters and lash caps. The new technique shown in the vid came out right where I wanted it with only one .015” rocker shim.

Witness mark

The new edited video

lcrken · Jan 20, 2018

Very nice, Jim. You're dead on about some of the big valve heads not having the stems line up properly. The one I'm using now for my 79.5x75 mm 750 cc short stroke has the exhausts pretty close, but both the intakes have the rocker arm adjuster hitting way off center, almost at the edge on one of them. I'm going to have to use a wear cap on the end of the valves just to get a decent wear surface.

I'm sure you could also do it properly with a mill, as long as you had good tooling that located off the rocker arm pivot. I'm actually surprised that it comes out so bad sometimes. The other similar head that I used on my 1007 street bike build was much better.

However, I also have three that started out as factory short stroke big valve heads, and were opened up for even larger valves, and they are spot on, so it certainly is possible to get it right.

Ken

oldmikew · Jan 20, 2018

lcrken said:
Very nice, Jim. You're dead on about some of the big valve heads not having the stems line up properly. The one I'm using now for my 79.5x75 mm 750 cc short stroke has the exhausts pretty close, but both the intakes have the rocker arm adjuster hitting way off center, almost at the edge on one of them. I'm going to have to use a wear cap on the end of the valves just to get a decent wear surface.

I'm sure you could also do it properly with a mill, as long as you had good tooling that located off the rocker arm pivot. I'm actually surprised that it comes out so bad sometimes. The other similar head that I used on my 1007 street bike build was much better.

However, I also have three that started out as factory short stroke big valve heads, and were opened up for even larger valves, and they are spot on, so it certainly is possible to get it right.

Ken

oldmikew · Jan 20, 2018

Its not just big valve heads on which this is a problem... some reputable source used to recommend judicioius bending
of the rocker arm with a pinch bar to achieve aligned status!It was said that the quickest 750s were not the combat engined bikes of 72 but those of 73 with the 32 mm inlets. Poor rocker geometry will adversely effect cam lift especially when the valve is beginning to open. Perhaps the factory improved matters on the later heads but mine was way out. Jim that is a very serious engineered solution.

jseng1 · Jan 20, 2018

Sideways misalignment can usually be fixed with shims on the rocker spindle. But front to back misalignment is a real problem. An alignment setup with a mill while the rocker is installed could be worked out (with some ingenuity) and the factory could nail it with a permanent jig/mill that was dedicated and adjusted to perfection through repetition.

But after thinking about the time it would take to align both the valve seat and the rocker arm on a mill (with each setup) I decided to just use the alignment tool doubled as the cutting tool. Most experiments don't always work out well (most fail) but this one came through with flying colors.

oldmikew · Jan 22, 2018

Jim
Yes shims is what I had to do to correct the sideways misalignment , front to back I had to leave not having the kit or engineering expertise to do anything about it. Shame . Its the original head on a bike I bought brand new . I used to live in South east London and was told that the operator responsible for installing the bearings in the cases used to press them in cold and actually make the cases flex under the press.. These no doubt were the ball roller configurations that used to come loose in the cases at low mileages... around 25,000 to 30,000. At least mine was assembled in Andover not Plumstead. And the bearings are still fine..

acotrel · Jan 23, 2018

I was under the impression that you guys were re-angling the valves when you fit bigger ones. Perhaps that is when you would machine so that the valve tip aligns with the tappet in the fore and aft direction and shim for the sideways ? Or are you simply talking about fitting larger valves without re-angling ? If you don't re-angle, are the cutaways in the pistons correct ? Fitting larger valves is not something I would do myself. If you machine the cutaways in the pistons, every time you replace one you need to set up and do that operation. And unless you use titanium valves, their mass must be greater - that affects the upper rev limit. That might not matter if your objective is to increase grunt without revving the motor so high.

lcrken · Jan 23, 2018

acotrel said:
I was under the impression that you guys were re-angling the valves when you fit bigger ones. Perhaps that is when you would machine so that the valve tip aligns with the tappet in the fore and aft direction and shim for the sideways ? Or are you simply talking about fitting larger valves without re-angling ? If you don't re-angle, are the cutaways in the pistons correct ? Fitting larger valves is not something I would do myself. If you machine the cutaways in the pistons, every time you replace one you need to set up and do that operation. And unless you use titanium valves, their mass must be greater - that affects the upper rev limit. That might not matter if your objective is to increase grunt without revving the motor so high.

You can go about 1/16" larger on the intake without re-angling the guide and fitting larger valve seats, and still be OK with most of the high performance cams. For some of the more radical ones, you might have issues with valve-to-valve clearance. Anything larger than that requires re-angling the guides. If you just re-angle the intake, and go with the usual 1.625"/40 mm valve, it will still be OK with most performance cams. Going to the larger intakes, or to both larger intakes and exhausts, can cause valve clash issues. The usual solution is to sink the valves a bit, and maybe radius the lifters, or just settle for a milder cam.

Ken

acotrel · Jan 23, 2018

I noticed that when I had the seats in my Triumph head cut with the three cutters, the motor picked up a bit of performance. Do the bigger valves give much further increase in power ? Where is the improvement - mid-range or top-end or both ? I noticed in one of Jim's videos, he did a wheel-stand with a featherbed Norton. I've wondered if that was dues to performance and gearing or the position of the motor in the frame. Regardless, it was pretty impressive.

Re-angled big valves

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