Topic: Oil starvation to part of camshaft. Blocked oil supply passage?

[Mr. Clutch]

Hello everyone. I've been reading the content of this forum regularly for tips and advice since I got my CB750 a year ago and finally decided to post a question, mostly because I'm stumped. I'm fairly new to motorcycle maintenance but I got an old bike to learn and, well, here we are.

Anyhow, I have a 1976 CB750F that I have been gradually upgrading. While riding at the end of last season, I started hearing a loud ticking noise from the top end. I immediately rode home and thinking it was the cam chain, reset the tensioner. I also double checked the valve lash adjusters for good measure. To my surprise the ticking was still there and to my horror transformed into a chirp as I listened to it idle. It sounded metal on metal. Riding season was over.

Fast forward to the present. It has been unusually warm in Detroit lately so I just pulled the engine today to see what's what. With the valve cover off, it was immediately apparent that there was an uneven distribution of oil in the top end. Despite not having been turned over for some time, the camshaft, rockers, and valves for cylinders 1 and 2 were still swimming in oil. Over on cylinder 3 there was less oil but still a considerable amount.

Everything beyond that (camshaft, lobes, journal bearing, rockers, valves) was bone dry. Sure enough, when turning the engine over by hand the chirp corresponded directly with the cylinder 4 intake cam lobe lifting the rocker. A drop of oil on the lobe cured the chirp. Also, sludge (or metal shavings from the lobe/rocker?) had completely plugged the oiling hole on the cam carrier at the far end of the shaft. Another interesting discovery was that one of the nuts on that same cam carrier was loose allowing that carrier some freedom of movement. Perhaps this is the source of the ticking I heard.

It seems clear to me that there is some serious oil starvation issue with the right side of the top end. I'm not very familiar with the oiling system but I think a passage to that part of the top end may be blocked. Judging by the oiling diagram there are two high pressure oil supply passages, one on either side of the cam chain.

What would be the best way to verify a blockage and following that how could it be cleared?

Thanks in advance for the help.

[05c50]

That's a somewhat common occurrence if the engine was previously assembled using silicone rtv sealer. There are a couple very small oil jets in the head that are easily plugged/restricted with little pieces of silicone. Debris and pieces of old gaskets can also cause the problem. You'll need to remove the cylinder head and block to inspect the oil passages. There may also be other internal damage caused by the lack of lubrication.

.....Paul

     

[seanbarney41]

05c50 is correct.  However, you may not have to remove the cylinder head to clear the blockage.  You will have to remove the cam towers.  The towers, camshaft, and rockers will need to be replaced anyway.  Under the cam tower should be 4 very small o-rings, 2 on the inside end of the towers and 2 on the outside end.  Underneath the 2 inside o-rings is the oil jets.  They can be pulled out gently with some needle nose pliers.  Make sure and clean these jets.  Whatever cam towers you end up using, make sure to flush all oil passages with carb or brake cleaner.  Remove the oil gallery plug on the rh side of the crankcase just above and to the rear of the points cover.  Flush the oil passages through the head and look into the oil gallery to see that cleaner is flowing freely.  Replace the 6 "puck" seals that go underneath the cam towers after re-torqueing your cylinder head.  Replace the 4 small o-rings.

When you get the engine fired back up, remove the 2 outside end  exhaust valve tappet inspection covers with the engine running to confirm that there is oil splashing out.

[Mr. Clutch]

Thanks for advice. This is turning out to be somewhat of undertaking.

Do they still make new cam towers and camshafts or should I try to source used ones?

[seanbarney41]

you can get new camshaft but you will have to source towers and probably rockers used.  Member Chewbaca5000 has good deals on these parts going on right now in the for sale section

[Mr. Clutch]

Thanks! I'll see what he has to offer.

[Kevin D]

https://detroit.craigslist.org/okl/mpo/5991621552.html

Hey there mr. clutch, I saw this Craigslist post in another recent thread. The seller is in Troy and has beaucoup parts.

[Rocky2010]

As I am doing a full rebuild on a CB750 and noticing all the oil galleries in the engine top end also the bottom end and everything in between if I were you I would be doing a full disassembly of the whole engine to make sure everything is clean as it can possibly be or you may end up having the same issue again.

[PeWe]

I have been thinking about oil starvation. Especially after reading all reports here and I have just finalized my build.

BUT, according to the oil flow picture shown in the shop manual, the oil to the head goes from oil tank direct to oil pump, oil channel in case via the oil filter, upper case (here o-ring 183), 2 holes with o-rings around the inner cyl studs, up thru cylinder, o-rings again, head via the small tiny oil orifices with o-rings and finally cam towers with its small  holes feeding cam bearings and holes for squirting oil on rockers. The final hole against head is a must to keep up the oil pressure by the 3:rd and 4:th O-rings for the blind hole.

Where can particles and sealer enter the oil flow?
- Hardly from oil pump that will work as a mill, but small things might pass. ( I want an oil cap with lock just for sure to avoid sabotage)
- Between cases where the 183 o-ring seal. I did not put sealer around this last time, sealer on the outer case side only.
- Maybe if cyl stud is locked with loctite or o-rings here fixed with sealer to make assembly easier or used sealer instead of base gasket.
- O-rings between cyl block and head, some use sealer just for sure despite most head gaskets must be installed dry.
- Oil channels in head, oil orifices maybe blocked when handling the head when working with it during the restore?
- Plugged oil channels in cam towers, also when working with them or way too much sealer around the rubber pucks that will flow to the oil feed.

I guess it is easy to get dirt in the oil channels when doing the rebuild.
Sealer elsewhere will not end up in the cam tower oil feed as I have understood it.

EDIT: Be careful when changing oil filter, dirt, sand etc can fall in here and enter the oil feed direct to the top and blocking the oil orifices?
Important to clean around here befpre removing the oil filter, remove oil filter cover, clean oil filter cover with degreaser and wipe bone dry. Oil filter bolt is hoow and can hide dirt too.

This is a very interesting subject to shed light on.

[Mr. Clutch]

https://detroit.craigslist.org/okl/mpo/5991621552.html

Hey there mr. clutch, I saw this Craigslist post in another recent thread. The seller is in Troy and has beaucoup parts.

Thanks, Kevin D. That's certainly worth a look.

[Mr. Clutch]

A little more information on what happened leading up to the blockage.

I only had the bike for the summer and changed the oil and oil filter once since I bought it in December to get it ready for riding season. I assumed all of the parts were in the oil filter housing but the next time I changed the oil months later I had just read through the shop manual and realized the little washer that acts as a seat for the spring on the filter was missing.

I kept the old filter (because for some reason I store and catalogue every part I change) and the washer wasn't stuck to it so I guess one of the previous owners had lost it. So I ordered a new one which took 5 days. There was no oil in the bike at that time.

The following weekend I installed the oil filter, filled it with oil, and hit the road. 50 miles later the oil starvation hit. It was pretty sudden, too. At one stoplight it was sewing machine smooth. At the next, tin man choking on wood screws.

[PeWe]

Good to know the background of this case.
I have also lost the washer and even the spring in the beginning, no problems. When removing the filter all black warm oil flows and easy to miss those parts when not aware of them.

I might been lucky and no dirt in that area. The oil sump however another story full with debris! This is blocked by the oil pump strainer and can only block it enough to reduce oil flow to transmission and back to oil tank. But if oil tank will get lack of oil, less pressure to crank and head.... This based on the oil flow page in manual.

[seanbarney41]

Plus one pewe...I have ran without the washer for many thousand miles and never had a problem

[Mr. Clutch]

Plus one pewe...I have ran without the washer for many thousand miles and never had a problem

I thought it was a minor component to worry about but I wanted to make sure everything was squared away as best I could. Now I'm thinking that letting it sit for 5 days without oil loosened something up like a wad of sludge or some gasket material that had an opportunity to dry out. Stuff like that can be a time bomb just waiting for the right circumstances to wreak havoc.

In hindsight I should have just let that washer go until the next oil change. But now I know for the future! Also, I now have an excuse to get acquainted with the engine's inner workings, as terrifying as that prospect is.

[ekpent]

 I don't think letting it sit for 5 days without oil had anything to do with it, not much 'drying out' would take place inside the engine. One of your task will be dropping the oil pan, might be some clues in there.

[754]

The holes are very tiny, mine finally failed on the road it had been warning me..it wore over a few months.
 I got the jets out, expected the one to be plugged but not that i could really see. I ran Qtips down the hole as far as I could no big blobs of anything.
My cases were replaced, and there is silicone squeezed out of the seam, but I did not find any.
I cut the frame and did it with head in frame.
 The warning sign I somewhat ignored was the valve setting getting looser on that side..a few times and increasing noise.
 I also recall one time it did not seem to want to kick over, so I used estart, and it fired up..I know suspect that at that point, the cam end was seized.

[PeWe]

Anyone that has inspected the oil flow at idle by open the tappet covers? Cam bearings and oil squirting on the rockers.

[ekpent]

  You did mention in an earlier post that the nut on the cam tower bearing stud was loose. If indeed that bearing shell was loose fitting on the cam it could create an oil film failure resulting in a burn out.

[PeWe]

Stud that is coming up?
Over tightened.... bad threads that need a thread insert plus teflon thread sealer for stud?

[Mr. Clutch]

  You did mention in an earlier post that the nut on the cam tower bearing stud was loose. If indeed that bearing shell was loose fitting on the cam it could create an oil film failure resulting in a burn out.

Hmm, that's right, there was a nut on one of the cam towers that was completely loose. I could see a breakdown in the oil film of this journal causing the debris I found in the oiling hole of that cam shell, but do you think it could explain the lack of oil to that end of the camshaft?

Here's a few pictures. The oil on the cylinder 4 cam lobes and rockers are from me adding a few drops to confirm that was the contact area causing the chirp. When I first opened it up it was completely dry beyond the lobes of cylinder 3.

[disco]

If one of your cam tower nuts backed itself off, I would say that you did lose some oil pressure in that cam tower. If the oil pressure dropped significantly, it may be possible the oil was only dribbling out of that cam tower & it was no longer squirting the oil onto the lobe of No 4?

[ekpent]

 This is the cam out of the bike engine I am working on now    Bought it as a basket case several years ago. One of the oil jets under the cam tower was plugged and the tower went dry. Ate both bearing surfaces on that side. Hope he made it home   

[Mr. Clutch]

If one of your cam tower nuts backed itself off, I would say that you did lose some oil pressure in that cam tower. If the oil pressure dropped significantly, it may be possible the oil was only dribbling out of that cam tower & it was no longer squirting the oil onto the lobe of No 4?

I'd believe that, disco. When I get to taking it apart I'll post some pics of the damage.

This is the cam out of the bike engine I am working on now    Bought it as a basket case several years ago. One of the oil jets under the cam tower was plugged and the tower went dry. Ate both bearing surfaces on that side. Hope he made it home   

I wouldn't expect my cam wear to be anywhere as catastrophic as yours, ekpent. I'm amazed that engine ran at all!

[ekpent]

  It sounds like you caught yours early enough and did not keep pushing it.

[seanbarney41]

They will fail fast... 15 minutes run time and a couple miles riding was all it took for one of mine to end up like Ekpent s