HD Panhead Valve Stem Height

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
dhidaka
Member
Member
Posts: 118
Joined: Sun Jul 25, 2010 10:19 pm
Location:

HD Panhead Valve Stem Height

Post by dhidaka »

I am restoring a set of heads for a 1955 Harley Panhead
All new seats.
New guides.
New valves.
All seat work is being done on a Rottler seat/guide machine.

I am sure there is a specified valve stem height when the seats are cut.
Can anyone help me with that spec?
hoodeng
HotPass
HotPass
Posts: 1092
Joined: Sat Mar 04, 2017 6:53 pm
Location: South Australia

Re: HD Panhead Valve Stem Height

Post by hoodeng »

OEM stem protrusion from the top of the guide shoulder is 1·500," service is 1·500"-1·540". Be aware if using an aftermarket camshaft that the TDC lifts can necessitate running more than the minimum stem protrusion from the outset to accommodate V To V @ TDC overlap. Minimum V to V ·060"-·080".

The 55 74"uses the same head ø valves in and ex 1·750", the lengths are in 3·800" ex 3·820" a number of stem ø have been used by different manufactures ranging from ex ·374" to ·376", in ·375" to ·377" you can use later Shovel guide clearances with these heads. These heads can be changed to the later 1·950" head ø inlet valve, be aware this valve is typically 3·885" long and will need this length factored in if you go this way with stem protrusions.

Spring test all springs to meet requirements, do not expect new springs out of a packet to be used unchecked, some after market springs need shimming from the outset. In a Pan you can run into top retainer fouling the inner rocker cover if you use high lift upper retainers, this can be rectified by using the OEM top retainer [or similar in set down] and making custom lower retainers without the inner spring raised shoulder, this will give an overall lower spring installed height setting, if this method is used be aware that a light fly cut and i mean light, just touch the casting to provide a seat for the lower retainer of about 75% any deeper and you will break into the inlet port.

Cheers.
MotionMachine
Guru
Guru
Posts: 1564
Joined: Thu Sep 16, 2010 10:01 am
Location: Virginia
Contact:

Re: HD Panhead Valve Stem Height

Post by MotionMachine »

I can't add much to that detailed response from Hoodeng, except that I rarely machine all of the original bronze seat out of the head, there is always a sliver of seat left on one side. I just ignore it and press new ones in, never had one fail. I'd rather do that then go to a larger o.d. seat. The OE cast-in seats are keystone shaped so you'll still see a band of bronze around the entire bottom of your seat pocket. I use .004" press fit and cool the new seats with nitrogen.

It's much easier to hit the the correct tip height while cutting the seats in the machine if you make a round sleeve 1.500" tall that sits on the guide. With a notch cut out on one side at the top of it you can see the valve tip and check you progress without having to roll the head over to measure it.
HDBD
Expert
Expert
Posts: 864
Joined: Sun Jun 01, 2008 4:32 pm
Location: Northwest

Re: HD Panhead Valve Stem Height

Post by HDBD »

Sometimes I use oversized valves if the seats are sunk close to limit to restore stock protrusion. On the intake it allows a better throat ratio and the SSR can be fixed to flow better. I always use the lower spring seats with reliefs to seat on the head casting not the guide boss. Kibblewhite seems to have done a pretty good job as one stop shopping with less fussing around.
User avatar
panic
Guru
Guru
Posts: 2295
Joined: Sat Dec 11, 2004 12:04 pm
Location: Ecbatana
Contact:

Re: HD Panhead Valve Stem Height

Post by panic »

The intake and exhaust valves are the same length and OD, but the material and shape are different. An exhaust is safe to use as an intake (try to match the shape by removing material from the stem-to-head radius), but not the other way.
Post Reply