1938 rocker shaft head seals

[slamiste]

I hope this makes sense because this is my 1st knucklehead assembly and I'm totally in uncharted territory for me!

I'm back to working on the 38 knucklehead. My next step is to assemble the heads. According to the service manual the rear exhaust rocker seal assembly includes (from the ball stud end):
Oil seal 120-30B (no fabric on either side)
Oil seal retaining washer 123-36
Oil seal 120-38A (referred to as the small oil seal)
Oil seal retaining washer 178-38 (small)

The assembly for all other rockers is:
Oil seal 120-38 (fabric side facing ball end stud)
Oil seal retaining washer 123-36

I have a seal kit from James that is said to be for 1938 - 1947 models. This seal kit includes 5 seals, all the same size, without a fabric side and have a I.D. bevel on one side. I tried to attach a picture of the seal but was unable to. My 1st addition Palmer notes that current replacement seals do not have a fabric side so I assume I have 5 seals that take the place of part number 120-38. I don't have small seal 120-38A or seal 120-30B for the rear exhaust position.

So, am I supposed to use 2 of the 5 seals in my kit to replace the 2 seals called out in the service manual for the rear exhaust position? If so in which direction does the seal bevel face?

If the seals I have won't work where can I I source small seal 120-38A and small seal retaining washer 178-38?

[bobphd]

The seal bevel faces the ball stud end of the rocker shaft so that the flat side is against the tin valve covers for proper sealing. The large James seals are very good but no they won’t work on the small end of the rear exhaust rocker. I am not sure who would have them but someone probably does. I scored a few originals years ago and that’s what I have been using.
Bob

[slamiste]

Thanks Bob.
Since the original instructions imply the "big" seals are the same except for the fiber issue and since the same big seal retaining washer is used in all 4 positions am I correct that 1 of the large James seals I have is OK to use in the rear exhaust position and I only need to source the "small oil seal and small oil seal retainer"?

[bobphd]

Yep that’s what I do. I believe the part no. For the rear exhaust smaller seal is 120-38a . A quick internet search doesn’t turn up much but surely someone knows or uses something else. Maybe ne of the larger James seals could be made a little smaller @nd made to work. Bob 810B3097-3229-45B1-BAB9-F3CA0C06D19C.png

[Rubone]

I used to have a few of those seals. If I think about it when I'm out in the shop I'll look. They would be old OEM if so.

[slamiste]

Bob and Rubone,
Thanks for the help and advice. If either of you have one you can spare that would be great.

Steve Slaminko

[bobphd]

I only have 2 of the oem small seals left so I don’t want to part with one but I took one of the new james larger seals and slipped it over a 19 mm socket and spun it with my drill press while using a flat bastard file and turned the od down to the smaller size. It took a bit but worked. I am doing the heads on my 40 and am going to use it on it instead of a 75 plus year old original rubber part. The smaller steel back up washer could also be made from a larger one as used in the other 3 rocker arms.
Bob

[T. Cotten]

What are the dimensions you need, Folks?

RKRSELS.jpg

....Cotten

[slamiste]

Good idea Bob,
Could you please supply the O.D. and thickness of the original small seal 120-38A.?
Thanks, Steve Slaminko

[bobphd]

According to my 41 parts book 120-38a is 1-15/32 “ and 1 is used. Also 120-38 is 1-1/2” and 3 are used. It also lists 120-38b at 1-33/64 and 1 is used. I assume that 120-38b was used as the outer seal in the steel adapter sleeve of the rear exhaust. The original 120-38a that I have measure 1-15/32, 1.469 od and .304 thick. All you have to do is get the outside diameter sized to fit snug into the inner inside diameter of the rear exhaust steel adapter sleeve. The width is not real important as long as the valve spring covers compress and seal into the outer seal in the adapter sleeve. I tryed to post some pictures but get error messages from both my iPad and iPhone. I get these even with pictures previously posted so there may be a problem with the message boards computers but who knows?
Bob

[slamiste]

Bob,
I really appreciate the time you've taken to assist, educate, measure and respond to my questions. I'm still a few months from assembling the heads so for now I won't take up any more of your time. Thanks again!

Steve Slaminko

[T. Cotten]

Mine are all ~1.460", Folks,..

Which makes me think they would be loose.

Might be why they survived!

....Cottn

[slamiste]

Thanks for looking into your stock for me Cotten

Steve Slaminko

[bobphd]

I was just looking at some eBay junk and I see that Taiwan Ted vtwin has both seals and backing washers with the adapter sleeve available as a kit. It is part no. 14-0455 and is about $80.00. A lot of his stuff is junk but some is not too bad. I would post a picture but that function is still not working for me.
Bob

[slamiste]

Hey Bob,
I saw that set was available from another supplier that has a less than excellent customer service reputation. I didn't want to order it from that source so I looked in my V-Twin catalog and couldn't find it. However, with the part number you gave me I was able to find it in the V-Twin on line catalog. I don't know if I'll order it or not but it's good to have the option.

Steve Slaminko