Author Topic: Rocker Shaft Trouble (Read 18650 times)

Groover · « **on:** March 01, 2012, 09:16:40 PM »

There is a reason Honda put 5mm bolts in the rocker pivot shafts and it is this:

When I started up my newly rebuilt motor it sounded like four cats simultaneously fornicating and fighting.
I shut it down and drained some oil only to find it impregnated with fine iron filings (and not-so-fine ones in the filter housing and the sump).
Engine out of the frame, stripped top and bottom revealed the 1 and 2 intake rocker shaft had been floating so much either side of the waist had been rubbing on the central hold down bolt, hence noise, hence metal filings, hence shiny bits in the picture,
Hondaman, have you actually run a motor without the 5mm bolts holding the rocker shaft, as per your recommendation in your book? Forgive me, but I am a little pissed off right now. Groover.

bikerbart · « **Reply #1 on:** March 01, 2012, 09:40:16 PM »

What?

mick7504 · « **Reply #2 on:** March 02, 2012, 05:07:04 AM »

Leaving the 5mm bolts out would not have caused that shaft to shear.
It looks like that shaft has bitten into the cam tower and then one of the rocker arms (or vice versa) and then twisted apart.
More than likely through lack of lubrication.
Are the oil jets in the head and the galleries under and through the cam towers clear?
I think that is where the problem is mate.
Extreme care in that department is mission critical when assembling the top end.

MRieck · « **Reply #3 on:** March 02, 2012, 05:42:06 AM »

That is interesting wear. I have seen the tower hold down bolts wear at the shaft groove (in the old engines) but not the shaft so much. If there was an oil problem the rocker arms, cam lobes/journals and cam tower bearing surfaces would be wasted.
Honda used the 5mm bolts to prevent shaft rotation which wears the cam tower shaft holes. They did the same thing basically to the later 550's as the holes can "egg" out. I have personally seen this occur more than 3 times on the 500/550's.

markb · « **Reply #4 on:** March 02, 2012, 05:51:40 AM »

I'm confused, what engine in the original post?

mick7504 · « **Reply #5 on:** March 02, 2012, 05:59:12 AM »

Strange thing is that it looks like a clean break.
I can't say that I've witnessed that before without some other collateral damage as has Mike suggested.
Those shafts should rotate freely after assembly, unloaded and without the 5mm bolts installed.
Are there any signs siezure on any of the mating surfaces?

MRieck · « **Reply #6 on:** March 02, 2012, 06:10:56 AM »

It certainly is odd Mick

MCRider · « **Reply #7 on:** March 02, 2012, 06:14:07 AM »

I don't think the hold down bolts appeared until K3 or so. Prior engines did not have them and ran fine. They were added to subdue some noise, but in locking them in place they cause an egg shape wear as mentioned by others. Leaving them (bolts) out should not hurt anything and should free up some friction causing elements.

ekpent · « **Reply #8 on:** March 02, 2012, 06:15:09 AM »

Is it actually broke yet or just been ground down in that one specific area. Does it look like it rotated at all as in other spots around the shaft.What year did they start those bolts,think it was around 1973 / K3. Also you mentioned that this happened on 'start up' so what you are saying then that this happened basically with 0 miles on rebuilt engine.? If so what on reassembly could cause that.

mick7504 · « **Reply #9 on:** March 02, 2012, 06:39:25 AM »

It has been indicated that leaving the 5mm bolts out does free up HP.
I guess that it has it's pros and cons, and at the end of the day I think that it comes down to an individual choice.

I am curious as to why this shaft has sheared apart.
There is a reason for that to happen and it isn't normal.

If there are no signs of partial siezure on the contacting surfaces, it would suggest to me that the shaft has been been subjected to some form of stress before the engine was fired.

markb · « **Reply #10 on:** March 02, 2012, 06:55:38 AM »

I must be the only one not confused. I'm assuming this is a 750 engine, not a 500. What year?

mick7504 · « **Reply #11 on:** March 02, 2012, 07:17:18 AM »

Quote from: markb on March 02, 2012, 06:55:38 AM

I must be the only one not confused. I'm assuming this is a 750 engine, not a 500. What year?

It's a 750 Mark.
Don't know what year Groovers engine is.
The early 750's ran without these 5mm bolts in the cam holders (factory) and then they were installed around about K3 or there abouts.
It's a take it or leave it situation whether to fit them or not.

MCRider · « **Reply #12 on:** March 02, 2012, 07:32:44 AM »

Groover, my point being that OEM CB750s in the tens of thousands were manufactured and lived long and happy lives without those hold down bolts. AS HondaMan and those of us who worked in shops at the time confirm, Honda made many changes which were designed to make the engine more customer friendly. The hold down bolts were to reduce the "sewing machine" noise in the top end, perfectly natural noise, as more fairings were being fitted and the noise was funneled up to the drivers ears.

By restricting the rotation of those shafts, they wore in one place. But Honda opted to accept the wear for the noise reduction. Even at that the wear would be minimal over the life of an engine. I love the sewing machine sound and i would take those 5mm holddown bolts and throw them in the bin without hesitation.

Your problem is a fitment/ oiliing issue, completely independent of the hold down bolts. I think i can see a wear groove in your picture just in from the left side. Looks like the pin seized or the rocker seized on the pin.

markb · « **Reply #13 on:** March 02, 2012, 08:03:21 AM »

Quote from: mick7504 on March 02, 2012, 07:17:18 AM

It's a 750 Mark.
Don't know what year Groovers engine is.
The early 750's ran without these 5mm bolts in the cam holders (factory) and then they were installed around about K3 or there abouts.
It's a take it or leave it situation whether to fit them or not.

Thanks, I've never worked on anything later than K2 so that was part of my confusion.

mrrch · « **Reply #14 on:** March 02, 2012, 08:33:50 AM »

I left mine out, no problems. Just have to remember when tightening down the stud that the rocker shaft will still turn (when overtorqued it will bind)

mick7504 · « **Reply #15 on:** March 02, 2012, 08:42:41 AM »

Here are the 2 different types from the Honda microfische.
The first one doesn't have the drilling for the 5 mm shaft bolts, and the second one has the shaft bolt holes drilled.

Early Type

Later Type

jaguar · « **Reply #16 on:** March 02, 2012, 08:59:00 AM »

im missing something here...

MCRider · « **Reply #17 on:** March 02, 2012, 09:20:26 AM »

Quote from: jaguar on March 02, 2012, 08:59:00 AM

im missing something here...

Parts #6 in the second diagram are 4 5mm bolts which thread into holes in the rocker stands and pin the rocker shaft in place so it can't rotate or slide side to side. The sliding was what was causing the excess "sewing machine" sound.

The first drawing early model engine does not have them.

excellrec · « **Reply #18 on:** March 02, 2012, 09:42:39 AM »

So are you still convinced it's from leaving the bolts out? I could see if this happened after a long period of time, but that sort of spontaneous wear based upon leaving out bolts that have been shown to have been omitted for years is clearly lacking in logic. This may be a case where the events are correlated but not likely causal unless you've got additional evidence to support this conclusion? I would probably be a bit more apprehensive before publicly denouncing hondaman

ekpent · « **Reply #19 on:** March 02, 2012, 09:58:08 AM »

I am going to be the first to float a theory and its something the OP can check.
The rocker towers have dowels in them in the ends on the underside and they also cover the infamous rubber pucks. If possibly one of the dowel pins did not completely seat,or jammed, or lets say a rubber puck came out of position and got lodged under the tower end that could possible alter the angle of the whole assembly and possibly induce some extra stress on the rocker to shaft to valve causing it to bind up and rotate very quickly together against the bolt.Sounds like it may not have ran long,but would not take long to do that. Also would do no favors on the lubrication front either.
Next--------

heffay · « **Reply #20 on:** March 02, 2012, 10:48:11 AM »

Who the heck is 7 post count groover??

fmctm1sw · « **Reply #21 on:** March 02, 2012, 11:04:35 AM »

Wow, looks like a beaver chewed that thing. It's time for some forensics.

MCRider · « **Reply #22 on:** March 02, 2012, 11:27:27 AM »

Quote from: fmctm1sw on March 02, 2012, 11:04:35 AM

Wow, looks like a beaver chewed that thing. It's time for some forensics.

I suspect we don't have the full story. Look at the shaft from left to right. Soon after entering the picture from the left you see a rounded indent in the shaft, top and bottom, indicating to me it travels around the diameter of the shaft. Ain't supposed to be like that.

The "wasp waist" where the action was, is there to let the main 6mm holdown bolt pass by. Should not be a touchy interference fit. Should pass by easily.

Without the 5mm holdown bolts, all that will happen to that rocker pin is a very benign tippy tappy action between the wasp waist and the main bolt.

"4 cats simultaneously fornicating and fighting" is likely an oiling problem IMO.

heffay · « **Reply #23 on:** March 02, 2012, 11:37:03 AM »

did it sound like this?

Senile Talking Cat! (The Original)

MikeKato · « **Reply #24 on:** March 02, 2012, 11:39:40 AM »

A search of his other posts showed that the PO had broken the camshaft. Looks like he made a lot of modifications to that motor so blaming it on that bolt sounds like a bit of a stretch.

"Full story"
http://forums.sohc4.net/index.php?action=profile;area=showposts;u=20557

Quote from: MCRider on March 02, 2012, 11:27:27 AM

Quote from: fmctm1sw on March 02, 2012, 11:04:35 AM
Wow, looks like a beaver chewed that thing. It's time for some forensics.
I suspect we don't have the full story. Look at the shaft from left to right. Soon after entering the picture from the left you see a rounded indent in the shaft, top and bottom, indicating to me it travels around the diameter of the shaft. Ain't supposed to be like that.

The "wasp waist" where the action was, is there to let the main 6mm holdown bolt pass by. Should not be a touchy interference fit. Should pass by easily.

Without the 5mm holdown bolts, all that will happen to that rocker pin is a very benign tippy tappy action between the wasp waist and the main bolt.

"4 cats simultaneously fornicating and fighting" is likely an oiling problem IMO.

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Author Topic: Rocker Shaft Trouble (Read 18650 times)