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Discussion Starter #1
Anybody have any info or links to reconditioning/cutting the valve seats on a T140V head? I think I need to do more than simply lap the valves on to the seats. Looks like I can buy for around $10 a 45 degree grinding stone (if that is the proper angle) and go at it myself. Anybody here done that themselves? I'm hoping I don't have to replace the seat itself on one particularly seat.
 

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The O.D. on the 45 should be 0.020"-0.030" smaller than the head size of the valve.
After you cut the 45,use a top cutter approx 30 degrees to get the outer seat diameter.

Cut the throat with a 60 or 70 degree included angle to get seat width to 3/32".

The seat should ideally be concentric with the guide,within 0.001".When new,they would have had 0.005" T.I.R. if you were lucky.Runout causes guide and stem wear,until the valve doesn't have to bend each time it seats.
You will have to push the cutter slightly toward the high spot,to eliminate runout.Hoping that the pilot stem won't flex,is just wishful thinking.
Just because a valve will lap in when it's cold and has plenty of guide clearance,doesn't mean the seat is concentric with the guide.

Cutters work better than stones,but you could do it with a stone.
 

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Discussion Starter #3
I've been unable to get to a PC for a few days and was very happy to finally see a reply. Thank you very much for those details. Its the details that count.
 

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I am a DIY person for sure, but when it comes to valve seats, the accuracy I can get even with my Neway cutters is far less than a motorcycle engine machinist. In my opinion, if your going to put real miles on it, let a pro do it! Call me lazy or scared but crank balancing and head work are the only 2 things I make sure to give to a pro.
 

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Discussion Starter #5
Re-reading Mr. Pete's posting above, it sounds like most T140V Bonneville heads didn't get manufactured to the tolerance they deserved. That would mean most T140V, even if running well now, would be better off with some valve reworking.
 

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Discussion Starter #6
Well, Dickie Doyle, you are touching upon a nerve with me on this topic. I'm trying to balance the DIY with the Do-it-pro (DIP ;-) ) approach and it a hard decision for me. On the one hand one has to consider one's capabilities (or at least one's interest and patience with learning something new) and on the other hand one has to consider the economics of buying specialist tools versus farming the work out. Pros have been known to do butcher jobs also, given that references are sometimes not accurate. So. I really don't know the answer, but I think I gain more in the long run if I DIY and get even some marginal success. I just wish there was more details out there on how to do this specifically on Bonneville heads.
 

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I understand the delema Aircool, I really do, and I'm sorry for hitting that nerve. My passion is vintage bikes but my profession is modern race bikes, so that nerve is hit every time I send a head out, seeing as I make much less profit subletting work out to someone else. I use a guy in Northern California who I trust completely, he has done fantastic work on anything from a 1930 model 18 Norton to brand new heads we are modifying for the Dakar Rally. You can PM me for his info if you'd like. They cut seats with a Serdi machine and are more accurate than anything I've ever seen.
With that said, there is something really special about the guy with so much patience and attention to detail that they dive into this themselves. Good luck!
 

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T140 Head

Having limited machining knowledge (and no specialist tools) I sent the head off too a local precision machinest along with new Black Diamond valves,springs and guides. In turn He advised I take the camshafts and followers to another specialist who only does camshaft work.

Head looks good-
 

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Having limited machining knowledge (and no specialist tools) I sent the head off too a local precision machinest along with new Black Diamond valves,springs and guides. In turn He advised I take the camshafts and followers to another specialist who only does camshaft work.

Head looks good-
Who would that be????as in nelson and about to do same...
cheers in advance
 

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Pros have been known to do butcher jobs also, given that references are sometimes not accurate.

just wish there was more details out there on how to do this specifically on Bonneville heads.
You can get it as accurate as anybody,provided you can measure the seat runout.You will have to push the cutter/stone toward the high spot,to avoid cutting more off the low spot.

Try this:
*Put a paint mark near the outer edge of the valve
*put a cigarette paper shim (0.0015" thick),or a piece of plastic film wrap from a cigarette-pack (0.0008" approx) between the valve and seat near the paint mark.
*Put enough shim (cig papers) on the other side (180 opposite),between the valve and seat,so that when you press down lightly on the valve-head you can just slide out the shim on the side where the mark is. It might be tight with 0.004" and loose with 0.005".
* Turn the valve 180 on the seat and check again.There might be 0.003" difference in the shim required,indicating some runout.
*Turn the valve 90 degrees either way,and check again in the 90 degree axis.

** If it looks equal at all 4 points,it's pretty good.

After a while you get the feel of any eccentricity,just by tipping the valve toward the mark and sliding it down onto the seat.You feel the valve jump slightly as it hits the seat.You can feel tenths of a thou with your fingers.

I've had jobs done by the high-tech experts who wouldn't recognise seat runout if it hit them.Point out the high spots,and they'll just turn them into low spots with the same runout.

If you cut the seat to the sizes I mentioned earlier,the seat will be good.If you want to narrow the contact width of the intake valve to 1/16",back-grind the valve at 35 degrees to get that.Leave the 45 degree seat in the head at 3/32" wide.


It's a good idea to re-face the valve at 45,and grind the valve-tip flat and square.


After this,be sure to check valve-spring seated loads.I'm happy at 65 lbs intake and 75 lbs exhauust after shimming.5 or 10 lbs less would satisy most people who never see 7000 rpm.
 

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Valve spring seated loads

I noticed mine were 60 & 70. Written on the box containing the cams and followers that went to the cam expert.
 

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Engine & Cam

Who would that be????as in nelson and about to do same...
cheers in advance
Engine machining done by Dirk Stobbe, Precision Engineer 26B Newnham Street, Southbrook, Rangiora-Ph 03 313 2125

Cams being done by Kennelly Cams, 32 Duke Street, Christchurch, Ph 03 366 3378.
 

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I noticed mine were 60 & 70. Written on the box
"Written on the box" is not necessarily what you get when you install valve springs.There are too many variables.

Valve/collet/retainer heights will usually only account for a difference about 0.015" in the height of the top spring collar (about 3 lbs valve spring seated load).
The height of valve seats,and how much they've recessed,can account for a lot more.1/16" seat recession is hardly noticable after a valve job,but will reduce spring load more than 12 lbs.
 

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Valve Springs

"Written on the box" is not necessarily what you get when you install valve springs.There are too many variables.

Valve/collet/retainer heights will usually only account for a difference about 0.015" in the height of the top spring collar (about 3 lbs valve spring seated load).
The height of valve seats,and how much they've recessed,can account for a lot more.1/16" seat recession is hardly noticable after a valve job,but will reduce spring load more than 12 lbs.
Sorry, those figures quoted were with the valves and springs installed in the head. The information was for the Guy working on the cams and followers. I guess those figures mean something to Him and may have a bearing on how He sets up the cam profiles and deals to the followers.
 

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Thanks for the info on the shim technique.
This is something I have always had problems with using my Neway cutters and one of the reasons I have switched to a machine shop in recent years.
I am going to dust off the cutters and give them a go on my 66 Bonney rebuild.
 

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Discussion Starter #17
I've been trying to understand what this shimming technique is actually measuring. I have some unresolved questions. The important task is to measure how concentric the valve seat opening is with respect to the valve guide, am I correct? And you want the practical maximum deviation to be .001 or less, correct?
Yet, as I interpret this technique, and by rotating the valve itself, it seems to me that one might be measuring how perpendicular the plane of the valve seat is to the long axis of the stem guide OR perhaps how concentric the valve itself is with the seat.
What role does the in-tolerance "slop" between valve guide and valve stem play in affecting this shimming/checking technique?

....
Try this:
*Put a paint mark near the outer edge of the valve
*put a cigarette paper shim (0.0015" thick),or a piece of plastic film wrap from a cigarette-pack (0.0008" approx) between the valve and seat near the paint mark.
*Put enough shim (cig papers) on the other side (180 opposite),between the valve and seat,so that when you press down lightly on the valve-head you can just slide out the shim on the side where the mark is. It might be tight with 0.004" and loose with 0.005".
* Turn the valve 180 on the seat and check again.There might be 0.003" difference in the shim required,indicating some runout.
*Turn the valve 90 degrees either way,and check again in the 90 degree axis.

** If it looks equal at all 4 points,it's pretty good.
 

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The valve-stem clearance in the guide has no effect on the runout you measure with this procedure.You will get some valve movement,when the valve and guide are cold.The seat will still be in the centre of that valve movement.You don't want it off-centre.

The valve stem will tighten in the guide,when they both heat up.There will be less movement then.
 
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