Board index Flathead Power-Technical Questions, Answers, and Suggestions Shovels pushrod tube seal leak

pushrod tube seal leak

Post Sat Jun 04, 2016 10:20 am

Posts: 219
Location: Georgia
All,
Being Flatheadless and Knuckleheadless now a days, I am working a Shovelhead with a problem. It appears I have found the cause of the leak at the front exhaust push rod tube upper seal. Leak has been there a while. I have changed from Oring type tubes to the larger type seal tubes. Leak on this 1 seal persists.

I have the push rods out and was looking closely at the way the tubes seal against the rocker box. I have stumbled across a problem. The front exhaust tube seat in the rocker box itself is machined at the wrong angle. This causes the tube to not seal against the rocker box all the way around it. If you hold the tube in the rocker box without a seal to where the tube is seated against the box, it doesn't point toward the tappet block. Pointing the tube toward the tappet block causes the upper seat to not sit against the rocker box all the way around. It is offset by at least 3/4 of the tube itself. The rest of them seem fine and are fairly closely aligned, pointed toward the tappet block seats. Doing the same thing from the tappet block side seems fairly accurate on all 4 tubes.

Has anyone ever ran into this before? If so are there any suggestions to machine the seat straight? It looks like it would need an end cutter measuring 15/16"

I know some of you guys come up with some pretty imaginative machining techniques ant this may take that.

Rocker boxes are 1979.
F

Post Mon Jun 06, 2016 4:13 pm

Posts: 152
Location: Carver, MN

It would seem that it would have to be one mis-machined rocker box from the factory, or else we would have seen nearly every Shovel out there with similar symptoms. If that's the case, I would think that using a known good rocker box to build a fixture might be the easiest way to proceed. Of course that would mean you need another box to work from, but that would give the advantage of allowing you to compare the angle on the good one to the offending box.

Post Sun Jun 12, 2016 6:50 pm

Posts: 219
Location: Georgia
All,
I will attempt to post pictures of the rig I made to grind down straight the push rod cover seat in the front rocker box, exhaust side. I used a piece of 1/4" threaded rod, a thick 1/4" ID by 11/16" OD washer and a 1/4" ID by 15/16" OD fender washer. I sandwiched a small grinding disc between the washers. Then I surfaced the grinding disc to the same size as the fender washer. The smaller washer was used as a guide. It’s the same diameter as the inside of the rocker box pushrod opening. It centered the rig and prevented it from chattering. The picture of the seat is about ½ way through the grinding and shows the incorrect angle. While I had the tappet blocks out I opened the drains to 1/8”. I will be going back with the thick blue seals. They seem a little softer than the black ones. I did have to take a good bit of material off to get it straight. That left 1 side of the seat pretty thin. I don’t think it will fail but the only other alternative is a replacement rocker box. I’ll try this and report back after I have run the engine a little while.
F
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Post Thu Jun 23, 2016 11:50 am

Posts: 219
Location: Georgia
All,
Bike has over 50 miles after the above fix. Push rods are dry and all seems fine. While I was in there I opened up the small drains in the tappet blocks to 1/8" and installed the blue (softer, squishier) push rod tube seals.
F


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