Topic: cb750 - Left Cam Bank Not Getting Oil

[senyah750]

Hi Everyone,

My first post, but 3 year member! I need some work done to my '77 cb750f2. Pretty sure the top end needs rebuilt, I'm hoping not a total rebuild. Any help would greatly appreciated! Here is a little back ground on the bike...

I bought the bike almost 5 years ago and have ridden it for only a few weeks where I live in Ohio. I was in college and did not have the funds/tools/know how to fix the carbs myself, when one of the floats got stuck open, pissing gas everywhere. I took it to a friend of a friend who, for lack of a better word, royally F***** everything. He had experience working on these old bikes, showing me pictures of pretty good work done to others, so I trusted him when he said fixing the leaky head gasket along with the carbs wouldn't be a problem. I was young and stupid and thought $200 and a case of beer was the best deal I could imagine! He had the bike for about 12 months before he was offered a job in Michigan and had two weeks to relocate. He slapped my bike back together and delivered it to my parent’s house in the Cleveland area. During that process he dropped the bike in the back of his truck on transport and put a nice gouge in the tank. He also stepped on the original side cover, shattering it beyond recognition (without replacing). He then dropped the biggest bomb of all (you can call it ‘Fat Man’ or ‘Little Boy’, whichever you prefer) and told me he dropped a bolt in the motor and I would need a “bolt extractor” to get it out. He never did tell me the location of the bolt and I never heard from him again. A real life nightmare that I was conscious for. He only pulled off the jugs, so I don’t think the bolt can be very far.. 

Since then, I’ve had a Harley guy (my best friend’s dad) take a look, as he felt bad as to what the poor bike had just gone through. After a year with him he felt too uncomfortable splitting the cases so I passed along to a long-time vintage bike collector and metric bike mechanic. I grew up with his son and I remembered all the times we would go to the Mid Ohio Vintage Days and ride his old dirt bikes. This guy also has done some maintenance on my dad’s beautiful ’78 KZ1000 and has kept that thing running pristine over the past couple years. “Perfect”, I think. I’ll leave the bike with him over the winter and he can get to it when he gets to it. Two years after sitting in his garage, he still has not found the time to work on the bike, so I went to pick up this past weekend. He rebuilt the carbs and had the bike running very smooth and quiet, and then after about 2 minutes of idling he noticed a small rattle. The guy told me to let the next mechanic know that the left cam bank is not getting oil. He also said when he would shut the bike down a quick “squeak” would arise. He explained to me that it’s a possibility that the replacement head gasket was not dry and the gasket sealant could be part of the oil flow problem. He told me it probably needs the top end rebuilt, however, he rode the bike in its current condition..

I really appreciate anyone's input! I'm tired of it sitting for years and years when she wants to be ridden. Hoping to get her back on the road this riding season. Thanks everyone!

[flybox1]

Sorry for your troubles.
One of the best things you can do going forward, is to document and ask questions here on this site before you do anything.  Start a build thread on the project forum.  pictures and details will help us help you.  You're gonna need to tear into it.
The folks here will steer you in the right direction.
FIRST: HondaMan....a member here on the forum.  GET HIS BOOK!!!  today!  It has most everything you need to get started doing the rebuild of this bike.  I did. 
SECOND:  Come to the realization that this bike may not be on the road anytime this year.  Depends on the time and $$ you can devote.  If you want to ride now, find something more modern while YOU do the work on this.
THIRD: YES, you can do the majority of this work, and the work you cant do, a qualified machine shop can.  No more hack jobs for cash and beer, OK!? 

If in fact silicon gasket goo was used, there is a very good chance it has clogged the small oil jets under the cam towers. 
You'll know, and probably see evidence of it if you do an oil change and drop the oil pan.

[madmtnmotors]

Wow, that sucks. You don't have many options that I can see. The process to resolve what you describe (if I were going to be the one fixing it) would go something like this:

>STOP RIDING THE BIKE IMMEDIATELY. As long as there's a loose nut/bolt floating around in there the potential for catastrophic failure is real and imminent. With the "left cam bank not getting oil" you are also on the verge of roasting the cam and the left cam tower beyond repair (if it's not too late already).

>The engine will have to be removed from the frame. Once liberated from the frame they are easier to work on when mounted on an engine stand.

>Now to trace the oil path to the cam you would have to pull the valve cover, cam, and cam towers to get to the oil control orifices (oil jets). Inspect the cam and cam bearing surfaces for evidence of oil starvation. The oil jets under the cam towers are notorious for getting plugged, especially if silicone has been used on case gaskets.

>If the left oil jet is plugged, then clear the obstruction and hope that there's no more flotsam and jetsam circulating through the oiling system just waiting to plug it up again (again, silicone on case gaskets is notorious for sloughing off these offending bits). Since this was likely the oil feed problem now we can skip to "STAGE TWO". If the oil jets were clear then proceed to the next step.

>If there is evidence of oil starvation (i.e. are the cam bearing surfaces showing excessive wear?), and if the oil jets are clear, then you have to be prepared to go deeper by pulling the head and cylinders. The F2/F3 (77/78) CB750 require an understanding of the subtle differences in the oil return paths to get them reassembled without leaks. They are different than the K models.

>Once the cylinders are off, you are at the point of origin and only need to verify that the oil feed holes next to the cylinder studs adjacent to the rear of the cam tunnel are unobstructed. Might be a good idea to pull the oil galley plug next to the points cover and inspect the oil galley for debris.


STAGE TWO:

>Regardless of where the top end disassembly left off, now we have to find the loose bolt. DO NOT FLIP THE ENGINE OVER! There's a chance that the loose nut/bolt may have found it's way to the oil pan. Drop the oil pan and see if there's a loose bolt in there. If so, the remove it and put everything back together. You could actually do this before removing the engine from the frame.

>If the bolt is not in the oil pan, now you can proceed to flip the engine on the stand an determine whether you can hear or see the bolt moving around. If so, fish it out and reassemble.

>If the bolt has not been located, further disassembly would be required. You could just put it back together with the hope that the bolt bounced harmlessly to the side or else your mechanic only thought that it fell into the engine.

Yeah right, and de-Nile ain't just a River in Egypt....


You got a bad deal by at least what I hope were well meaning friends/mechanics. There's no "magic bullet" to fix what you have described.