Topic: It desn't take long to destroy a cam...

[KB02]

The oil jet in the head looked good and the passages were clear in the cam tower, but it looks like somewhere below that jet, I had a blockage on the right side of my engine's oil passages. Less that 400 miles on the bike since rebuild.






I had an oil leak, I suspect this puck was the problem. Don't know if it was even related or not to the death of the top end.

[sangyo soichiro]

Man... I'm sorry to hear that.   

[andy750]

Oh man...sorry to hear that.

I also have an oil leak on the right upper corner of my freshly built 810cc engine....unknown location of where its leaking from  - looks to be very near #4 exhaust at the nut just in front of the spark plug.....20 miles on the engine...teardown time here as well  










Was yours leaking from the same location??

thanks
Andy

[sangyo soichiro]

Dang Andy... sorry to hear about that too.  Hopefully it's an easy fix.

[rickmoore24]

Sh!t, F@kc, Damn!! That really blows, sorry to hear that.

[MCRider]

If I may, having had experience with both problems. The puking cam comes from a blockage in the high pressure oil orifice as KB alluded to. Many of us have suffered this, usually with the cam seizing in the holder and breaking in half with an audible "ping!" It is completely unrelated to an oil leak. The entire problem can occur in an engine which otherwise has no external symptoms. The fact that there are external oil leaks is a coincidence in my mind.

I've had the mysterious oil leaks as well. AS Andy points to, the oil drips out of the MIDDLE fins of the head. It comes from the forward, outboard, hold down stud of the cam bearing. That hole is open to the atmosphere, if you look in the fins as Andy was doing with his pictures, you can see the threaded opening of the hole.

We've talked on the forum about this leak before. Some builders remove that stud and reinstall it with thread sealer. That seems to work.  I was never able to get mine to stop leaking once it started, but i had other problems like the threads were stripped and helicoils and invited the oil to wick its way down and out that hole.

That's what i think.

I have replaced that head with a fresh head for my current build. I am also going to use a reinforced rocker box. Partly for my theory that if one removes the pressure from that stud of the big bump cam and springs, transferring it to the rocker box, it may not leak. The reinforced rocker box will also push down on the cam bearings helping to seal those rubber biscuits as well.

[KB02]

The only reason I suspect the leak to be a part of the problem was the proximity of the bad puck to the oil jet. The other side (with good pucks) looks fine. My leak was coming from right in between the center cylinders. I couldn't tell just where, but somewhere between the two. That puck is just to the inside of #3.

I just sat down and made out a spread sheet of the costs I have incurred on this project so far. Parts (and some shipping) alone has come to over $5100. Now I am looking at another $4-500 to get it going again. My Wife's and my first child is coming next next month. Money will be a bit tight for a while. I have no idea when I'll get this bike going again. Almost makes me just want to sell the thing and be done with it.


Does anyone know if the rocker arms from all year 750's will swap out? I saw a set from a 72 on ebay. Mine's a 78.

[MCRider]

KB, your leak may be coming from the inboard, forward hold down stud. Was your puck actually not seated in its hole after assembly? I can't tell from the picture what you think was wrong with the puck. I'd be surprised you could bolt the cam bearings down if the pucks weren't seated. If the puck weren't seated, and the bearing didn't seat, oil pressure could have escaped and resulted in your failure.

These holes (all 4 in total) dump out on top of their respective spark plugs, at about the 3rd fin down level. I'm going to get a picture now to illustrate.


You can see the ice pick inserted in the hole where the hold down stud goes. The pick emerges directly above the respective sparkplugs.

With wind currents from riding, the oil is blown sideways, though some will pool in the plug cavity, and it emerges from the fins in the front, in the case of the inboard holes and on the sides in the case of the outboard holes.

When this first happened to me, I like to play heck figuring it out. Finally one day I had it all cleaned up. Then i looked in with a flashlight, where Andy was taking his pictures, while it was running, and could see the oil drip, drp, drip, pretty fast out of those holes.

It could be the pucks, but my experience points to these holes.

[MCRider]

A little more explanation, if those studs have been removed and the threads disturbed, you start down the road of a leak. When reinstalling the studs, thread sealer is needed. Even if the threads weren't disturbed, a big bump cam and springs will exert a lot of lifting force on those threads and they distort allowing the oil to wick its way down.

Same thing happens with the pucks, but i visibly saw the oil coming out of the holes.

Obviously not all built engines leak like this, mine had had the studs in and out several times, ultimatley with helicoils.  I do think the reinforced rocker box will help.

[KB02]

Thanks for the explanation. For the life of me I couldn't figure out what you were talking about. It has literally been over a week since I have run the bike and it has taken about 200 miles on the back of a trailer to get it home (broken down on vacation at a motorcycle rally...). I can put my finger under the bottom of the hold down bolts where they come through and they seem to be dry. Still a possibility though, I suppose.

To try and show what I mean about the pucks, I took a few more pictures.

Top View:


Side view:


Bottom view:

(The missing chips are my fault - it fell apart as I was taking it off.)

They all appeared to be perfectly seated and came off the head when I took off the cam holder.

[MCRider]

KB, in your case the blown out puck is more likely your oil leak granted. Never seen a puck like that before.

So that can be solved. I think some non-hardening gasket goop on the pucks is de rigueur as well.

Don't think it had anything to do with the cam burning up. Debris in that oil hole, especially after a rebuild is most likely.

In my case I had rebuilt my engiine, 888 kit etc.. After a few miles took off from Indy for the West Coast. Toasted the cam in Tucson, just 20 miles from a buddies house. Rebuilt the top end (I had the APE frame rail kit) in a buddies car port with parts from local salvage yard. Finished the trip. Real adventure.

After the re-rebuild about 30K of uneventful miles. Till the weird oil leaks developed.

[mrrch]

Good info about those studs. i have the head off my 77K and one of the other studs is loose, will have to add some sealer upon reassembly. Possible oil leak caught in time.