Knucklehead Scavenging

[billpedalino]

I just removed the heads from my 1947 FL because of leaks between the valve cups and the heads. Also, I had just finished the motor (it sat for a while) and it was burning oil with less than 20 minutes running time. Obviously, someting is very wrong.

After removing heads, I noticed oil in the intake track and also perched on top of the intale valves; also wet oil on the pistons. After removing the upper valve tins, I noticed that a couple of the valve cavities were filled to the brim with oil. Furthermore, all four push rod tubes were oil-filled to the top. Obviously, the top end is not scavenging.

1. I removed the rocker box/rocker arm assemblies and blew through the return lines and (infortunatley) all were clear.
2. I have not removed the cam cover yet, but I would be shocked if I installed the breather gear out of time - I've done many,many motors and always doube-check this. But.... I'll re-check.
3. The push rod tubes are new, each with three new corks and showed no leaks. I assume that the vacuum circuit is sealed.
4. There was absolutely no leaking from the seals in the rocker boxes or the upper/lower valve tin gaskets.

The overhead oil line is full-open and I plan to throttle it down by reducing the orifice to .060". But my gut is that the poblem lies elsewhere, as there is still too much up there for that to be the sole problem, especially given the oil-filled pushrod tubes. If I remove the cam cover andf it's full of oil, there might be a sheared return key in the oil pump, but there is no oil comming from the primary oil snout, so the lower end is probably not filling up, so that's probably a long shot.

I will continue my analysis but was wondering of anyone else has had a similar experience?

[Rubone]

Bill,
What tappet guide gaskets are on there? The scavenge holes in the tappet blocks must be clear. Is the Breather gear a correct Knucklehead type with the scavenge hole in it? Is the case passage clear to the tappet guide bases? Are the tappets the solid original type and not the drilled ones as supplied by Eastern? Pushrod tubes should be empty when running. I have never used an oil line restrictor on any of my Knuckleheads and never had an oiling problem.

[billpedalino]

I've never had to reduce the feed either Robbie. But this is an odd problem, at least to me - I've done my fair share of knuckle motors over the years but never encountered this situation before.

1. I pulled the tappet blocks, and the gaskets are properly agligned with the drains fully unobstructed.
2. I ran a pipe cleaner through the tappet drain channels to the breather gear and also blew air through them - totally clear.
3. Yes, there is the knuchlehead breather gear with the hole in the circumference. After turning the motor a few times, I noted that all timing marks were lined up correctly.
4. I'm using replacement lifters, and they are from Eastern (from when I worked there many yeras ago) but are solid - not the drilled ones. However, I forgot to check that the scavange holes in the lifter blocks remain unobstructed by the lifters at the cam lobe's high point.
5. I am using aftermarket replacement valve cups and the intakes did NOT have the drilled vacuum-break holes, which I must install. This may account for the full intake cups and leakage past the guides into the combustion chamber. But then again, the intake pushrod tubes were full not long after shutdown so it appears that the vacuum scavenging from these cups was working.

One thing comes to mind is that I didn't think to check how dry the pushrod tubes were when the motor was actually running. I noticed that the pushrod tubes were filled after the motor was shut down for about an hour. Maybe (and this is a long shot), if the breather gear was at a position where the vacuum hole was not aligned with the drain channel hole when the motor stoped (pistons heading down), then the oil in the pushrod tubes would sit there and slowly drain out past the breather gear. Does this seem feasible?

I'm not sure exactly what's going on here - everything is clear and unobstructed. This is an interesting one. I'm excited about finding the cause!

[rousseau]

Bill
I think you hit on your problem with #5. I was going to suggest to check the "bleed holes" in you tins. Do NOT restrict the oil to the top end.

[billpedalino]

I'm ready to reasemble the valve guides and cups and I was wondering about the rocker shaft penetration holes. I didn't see any evidence of leakage beneath the valve cups. It was very hard to know for sure, but the lower cup gaskets looked dry. I do know for certain that the upper gaskets and rocker box seals absoultely did not leak. I really don't think that my original job of sealing the cups was defective in any way, as I've done a lot of these and never had a leak. Buttt.... I don't do this for a living anymore and, most certainly, there's always a first time.

I'm now thinking that because the oil level was so high in the cups and because of the oil-filled pushrod tubes, that the oil may have leaked out at the rocker shaft holes. Therefore, I'm now thinking about how I would seal this area without introducing sealant in the wear area between the left end of the rocker arm and the valve cup.

Has anyone seen this occur (I've never seen this) and if so, how did you correct it?

I'm embarrassed to say it, but so much of this 'evidence' seems more and more to suggest the possibility that there was too much oil in the lower end/oil tank. If so, how it got there is another story altogether.

And the saga contimues....

[billpedalino]

I notiecd that S&S, and possibly Jims makes a gearcase breather valve with an elongated top end vacuum orifice - its a slot rather than a hole. As my motor is still in a 'search and discover' level of disasssembly (again) while still trying to pinpoint the casue of the above discsussed scavenging problem, I'm trying to exhaust possblilities.

Supposedly this breather allows more vacuum time during the piston's up-stroke. I could not find this part on S&S's online catalogue (a user-hostile site for restoration guys, in my humble opionion) and I could only find it from a 3rd-party online source, who hasn;t answered my email inquiry. Does anyone know if this part is stiull made by S&S and where it might be acquired.

In the meantime, I need a break from the frustration so it's back to the Sportster today for some frame painting....


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[painterdale]

Guess I was hoping you would show us some pictures of your frame painting, Bill! Dale

[rousseau]

(5. I am using aftermarket replacement valve cups and the intakes did NOT have the drilled vacuum-break holes, which I must install. This may account for the full intake cups and leakage past the guides into the combustion chamber. But then again, the intake pushrod tubes were full not long after shutdown so it appears that the vacuum scavenging from these cups was working.)

Bill
The tins (valvecups) must be vented to atmoshphere. You do not want to (pull a vacuum) inside the rocker boxes. As the oil pools in the cups it is scavenged by the vacuum in the push rod tubes. If the tins are not vented you create a vacum inside the rocker boxes and your push rods act like straws pulling oil into them when the engine is stopped. Also if oil leaks or weeps from the vent holes, it's usually becauce the push rod tube seals are failing or installed wrong. This was my experience.

[larry]

I modified a stock breather gear to resemble the S&S gear. It did in fact increase the scavenging rate with no apparent negative effects.

[billpedalino]

Dale,

I painted the Sportster frame yesterday and for an amature painter like myselfe, it came outstanding! I will post photos this week.

Rousseau,

Thanks for the suggestions. I changed my original valve cups to new (aftermarket) as well and I did have to drill the vent holes. The pushrod corks (not the rubber seals) are new as well. Also, I noticed that the exhaust pushrod tubes are filling up with oil - not the intake. I'm going to plug up the cam cover end of the drilled return hole this week and see what happens - the gasket area did not line up well with the hole. I just don't want to go through all of the work involved in checking the heads (again) when I know that they are correct.