Topic: Worn rocker shaft holes in CB 750

[754]

 Anyone ever see this happen? I have not.
 I have yet another top end noise, clearly something wrong. I suspect a piston. I suppose if a rocker shaft were loose it may clatter.  It is the only other thing I can think of that could  make the noise. I  have had a lot of valves needing adjustment often, but valves seem to be wet and oily so I don't suspect blocked oiling.
 also in the past I have had a knocking rod,  and I dont think it is that.
 I am asking because I have never seen them wear, but if it was it could get noisy.. be way easier to fix than a piston.
 I should pop valve cover and have a look. soon.

[PeWe]

Threads for cam towers/holders in head OK? If not, cam towers might come loose.

[bryanj]

The 500's wear because the shafts can rotate but all the 750' lock in some way as i remember so there should not be wear there. Have seen vavle tips and adjuster screews badly worn

[MRieck]

 Have seen 500/550 shaft holes egg out but not on the 750. Maybe the early 750 with the non pinned shafts could wear out the holes but I haven't seen that happen on those towers either.

[rotortiller]

From reading your posts I'd say you know what you are doing. I would pop the valve cover and cam chain tensioner and work down. Maybe pull the pan for a snoop too. You don't seem the type to over look a loose tappet or exhaust leak

[jgger]

Hey Frank, if you contact member Scottly he can probably set you up with a frame kit. That would make it easy to pull thr rocker cover.😁🙊🙉🙈

[754]

 Actually I am  embarrassed  to admit this. .
 I cut my frame about 3 yrs back , to do my yearly top end fix.. or motor change.
 And so where along the way I sold my kit, probably have most of one here..
 
 Current motor, went in last summer, sold to me as rebuilt..78F.
was spectacularly quiet at first, but with in about 800 miles mostly highway had tappet noise.. . which continued. Adjust every 700 miles or less, I suspected soft valve ends from being ground. Until August, I switched to Rotella to get a higher zinc content. that seemed to quiet the valve clatter down, but I suspect it was masking the other noise,  which  is there once it warms up., a distinct rattle from right side..

 

[seanbarney41]

What are those soft valve ends and tappets looking like?  Are they pitted and worn concave?  On my 78f they were by 20,000 miles.  I kept replacing tappets, but could do nothing about the valves.  So it made a lot of extra noise that could not be cured by valve clearance adjustment.  I just lived with it as it ran good otherwise.

Until by 28,000 miles, it was using a quart of oil with every tank of gas and smoke screening those behind me(which was most everyone cuz it was still making that great 78f power!).  I assume this was the guides going bad but I have not torn it down yet.  That bike is gonna get a full restoration here sometime.

[my name is nobody]

Dunno if this is true, but
I read somewhere that rocker shafts can wear on later models that have bolted (pinned)
style rocker shafts, and since they don't spin, they wear. The shaft can be rolled over 180deg. so
the non wear area on the other side can be used, till it wears out. I'd check the shafts and rockers as well
in the pivot areas for scarring. Just a theory tho. iirc the factory tried to quiet the valvetrain by pinning'the rocker shafts, but made it worse.

[goodtryer]

It's in Mark's 750 book, the inspection chapter I believe.

[PeWe]

Cover off and reveal the root cause?

[Dunk]

I was wondering about this with regard to my K1 recently. It has a slight intermittent tapping, well more of a quiet ticking. I notice this come and go at idle sometimes. I wonder if it could be the cam towers wearing from the rocker shafts spinning. When I went through the top end I followed Hondaman's advise to allow the rocker shafts to rotate and drill the cam towers, chamferring the holes, to allow splash oil to lubricate the rocker shaft to cam tower area. 6000 miles since restoration. I kind of doubt this as I know he has done this and put far more miles with this modification, and the early models allowed the rocker shafts to rotate without the added oil holes drilled. For what it's worth all exhaust valves and all 8 guides were replaced 6000 miles ago. Valve and cam chain adjustment maybe 500 miles ago. I do need to sync carbs again though, so there's that. I'm not particularly worried at the moment.

[maxheadflow]

If the noise changes under load, you got a scuffed piston or something else wrong with the piston/pin /crank.  If it make more noise hot than cold, it could be valve train.

[754]

I have not opened it yet,  its my only wheels.
 I am thinking to have a least a full side of rocker cradle, rockers and cam ready when I do.. just in case. it seem to be right side
Monday I tried to have an engine builder buddy listen to it, but it was very cold out, had cooled off fast and was quieter  as it had sat 1/2 or more...... so much quieter with cold oil
 He did mention, that piston problems tend to be louder than most engine noise and I should try the screwdriver listen to try to narrow it down.  Will open it up maybe Sunday.

[scottly]

What are those soft valve ends and tappets looking like?  Are they pitted and worn concave?  On my 78f they were by 20,000 miles.  I kept replacing tappets, but could do nothing about the valves.  So it made a lot of extra noise that could not be cured by valve clearance adjustment.  I just lived with it as it ran good otherwise.

Good point, Sean. Isn't the crutch for the soft valve stems lash caps? Mike??

[bryanj]

With your knowledge on these and you not being certain i am interesred in the end fondings!

[754]

Well I give it a listen with a metal rod, definitely #3 clattering. Last time I checked them 3 intake was at 5 or 6 thou, about 2 or 3 weeks running time.. did not sound like pistons. . so I picked up my One Night Cam kit. to get ready. better inspect those parts.
 if it's rocker cradles or above , it should only take like 3 hrs.. unless , unless itx a really bad guide. that would suck.
 I am thinking one rocker cradle maybe, shafts and a few rockers.
  I will have to wait a few more days.

[BPellerine]

Well I give it a listen with a metal rod, definitely #3 clattering. Last time I checked them 3 intake was at 5 or 6 thou, about 2 or 3 weeks running time.. did not sound like pistons. . so I picked up my One Night Cam kit. to get ready. better inspect those parts.
 if it's rocker cradles or above , it should only take like 3 hrs.. unless , unless itx a really bad guide. that would suck.
 I am thinking one rocker cradle maybe, shafts and a few rockers.
  I will have to wait a few more days.
[/quote
I was going to suggest the screw driver listen,hope it is not too serious frank,bill

[RAFster122s]

Sorry to hear the 750 is not healthy. Hope the damage is not extensive. Good luck with the work, hope things go smoothly.
David

[754]

 Well I got it apart,  as in take valve cover off..
 a few surprises..  before I pulled rocker shafts out, I could feel a worn guide on #3 exh... then I pulled rear rocker shaft. the rocker was really bad worn in 2 different flats or sections  and shaft is dark and shows wear.  surprisingly cam lobe was not bad.  so I pulled all the rockers for 3 and 4 and  most had flaking and were marginal. so I pulled the other 4. most of the rockers had flaking or visible wear, 1 of 8 maybe I would call good.   and some wear on the shafts you can feel it. and some more worn guides, I would say maybe around 10  thou movement, as an educated guess.
 So I think   I will change all rockers and shafts and leave cam and towers intact. . #3 bad rocker looked less oily but valve had oil on top. Valve stems are not cratered but I will check again tommorrow and run a wire into #3 rocker feed hole, see if something comes out.

 Oil Pump Issues.
 I first noticed this on a warm day, crawling along a rocky rutted logging road in first and second gear.  at idle oil pressure drops to near  zero maybe 5 lbs, but if you rev it up to 3or 4 grand it comes back up to over 20, but not full pressure.  riding down the highway  is fine. stop and go traffic, sitting at lights it starts to go down if hot  .
 so that could be a contributing factor. .
 

[bryanj]

Guides will eventualy cause seal failure the lots of blue smoke and oil consumption but rarely stop motor running, sounds like you may have an oiling problem, either worn pump or excess clearance on crank, never saw either back in the day but we are 40 years on now.

[PeWe]

Bad oil not doing what a CB750 need?
Too thin like 10W-40?

[HondaMan]

Have seen 500/550 shaft holes egg out but not on the 750. Maybe the early 750 with the non pinned shafts could wear out the holes but I haven't seen that happen on those towers either.

This is my thought, too: Honda added the little 5mm bolts to the rocker shafts in the late K2 to quiet the top ends down when used with fairings that reflected the engine noise into the riders' faces. It isn't much noise, sort of a 'tinkle' sound, but real when the shafts wear a little. They rock up on one end (that is opening a valve) when the opposite end is loose, and the shaft 'clicks' once each cycle. At 138,000 miles I finally replaced mine (K2, pre-bolts type) to quiet things down a bit. The rocker towers' holes have worn to about 0.0022" average clearance (over the new shafts) now, and using the 20w50 oil quiets them a lot. OEM clearance here is less than 0.0010" new.

[754]

 OK , changed rockers and shafts, set at 3 and 4 thou, as Hondaman suggested, to let it lube a bit better.
 it has quietened right down sounds very nice. big load off my mind. I almost pulled the little bolts out if the shafts, but the big long bolt on one felt like it was stripped, so I left them in.
 I looked at my oil guage, I am thinking when hot at idle it may have been around 10 psi, if it is accurate, so it seems low but is getting oil , I hope.  I have Rotella 5-40 in it, and it seemed quieter as son as I changed to that a few months ago.
  Looks like I will get thru the season , but will keep an eye and ear on things .

[BPellerine]

well good for you frank,I was going to use an f3 top end on a motor but quickly changed my mind when reading about them,seems to be hit and miss how they wear,good for racers I guess.bill