Valve seat, top collar, fitted length

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Excalibur
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Valve seat, top collar, fitted length

#1

Post by Excalibur »

More dramas from this beaten up Shovelhead..

Found: top collars aren't a matching set...
cm1.jpg
There are 3 like the one to the right. My hunch is the one on left is Evo or early Shovel? They are same except for about .060" extra height. My thought is to turn it down so it matches the other 3. Simple job. Then there's enough valve travel clearance for a seal. Sound reasonable?

Found: Marks on inner rockerbox as pictured. Measured stem protrusion and yes, it's about .080"/2mm over max spec. Studying it closely, it's the spring that's made the marks. Spring protrudes the collar OD.
cm2.jpg
This is the rear exhaust and is the one that had the manky guide hole. Been studying this issue for some time. One way to solve it is to fit a new seat. Reading stories of seats coming out. Various seat materials, methods of fitting and clearances. Seems like some risk at least.
By the way, is 18010-79 the right seat? I could get this local but who to trust with the work is the big question.... and what is the interference fit spec?

Feeling confused and frustrated. Please post thoughts, tips etc that might help. Thanks.
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RooDog
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Re: Valve seat, top collar, fitted length

#2

Post by RooDog »

$&$ addresses the inside of the rocker box in their Shovel head instructions. No big deal, just relieve the inside of the box....

https://assetcloud.roccommerce.net/file ... 130218.pdf

I feel it is best not to replace valve seats and would rather replace the head with one having good OEM seating rather than risking damaging the rest of the motor should an installed seat fail.

Trimming the bottom of that upper collar would seem OK to me.
....RooDog....
PanPal
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Re: Valve seat, top collar, fitted length

#3

Post by PanPal »

Wouldn’t a oversized valve, new guide and new grind on your current seat not help.
Mongrel505558
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Re: Valve seat, top collar, fitted length

#4

Post by Mongrel505558 »

RooDog wrote: Sun May 08, 2022 2:46 pm $&$ addresses the inside of the rocker box in their Shovel head instructions. No big deal, just relieve the inside of the box....

https://assetcloud.roccommerce.net/file ... 130218.pdf

I feel it is best not to replace valve seats and would rather replace the head with one having good OEM seating rather than risking damaging the rest of the motor should an installed seat fail.

Trimming the bottom of that upper collar would seem OK to me.
....RooDog....
I had a replacement seat drop once. No fun. Luckily not all the way out, but it wouldn't allow the valve to close all the way and the piston whacked the valve on the next trip up. Result was a bent valve and a dinged piston, plus it happened at the top of a bridge about 30 miles from home. Had to call a friend with a pickup truck and luckily someone saw the two of us struggling to lift the bike into the back of the truck and stopped to help. I haven't had a seat replaced since. I like PanPal's suggestion of an oversize valve. Then you can start fresh and cut the existing seat to give you the valve height you need.
Andygears
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Re: Valve seat, top collar, fitted length

#5

Post by Andygears »

I have recently been made aware that shorter stem valves are readily available, with the keeper groove 1/8” further down the stem toward the valve head. This can solve the protrusion problem, but the sunken valve head can hurt performance.

Andygears
Excalibur
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Re: Valve seat, top collar, fitted length

#6

Post by Excalibur »

I think it can go together this time with a bit of relieving of the rockerbox. It's 5mm/0.2" thick.

Andygears, can you post a link to those shorter valves please?

Springs: My heads are late 82. I note there was a change of spring during '82 to a shorter free length of 1, 3/4" whereas early was almost 2".
Both fit to 1, 3/8" fitted length. What's known about this change of spec? Will either springs actually work in either heads??
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