Topic: Tappet adjuster cover clearance

[graeme7]

Ive put 120 miles on my new to me cb750 so far.

I've done a fair bit of maintenance including tappets and timing.

The other day it was tapping, always has a little. Increased with revs but almost dissapeared at idle. I decided to go over everything again, all was fine, then as i went to re-fit the 8 adjuster covers i noticed one had internal damage where the adjuster nut had been hitting it.

I dont understand why though. I have a few spares, i have 7 that are slightly thicker (about 0.8mm deeper inside) and 5 thinner.

Are the thinner ones from a different model?

I had 2 of the thinner ones fitted though and only one is clipped. All the adjusters protrude from the cam cover by the same amount when the valve is closed.

Maybe one was on an inlet? The clipped one was on an exhaust valve for sure.

What could cause a rocker to lift of the valve like that? All i can think is if the cam flexes, or if the rocker shafts move. (it was NO.3 exhaust the clipped).

Ive not had the engine out so cant take the cover off to examine. I dont know these engines so i dont know if the above suggestions are even possible.

Wondered if anyone can shed any light on this, i have to use one of the thinner ones, i guess im best of using it on an inlet.

[graeme7]

Pis of the damage, no marks at all on the adjusters though.

[graeme7]

Been thinking about this and im not sure it can be a symptom of other wear inside (rockers, shafts etc) as this must have just happened.

Ive had these covers of before, paying no attention to which hole they came from or went back in.
So unless i was super lucky and got the same cover back in the same hole this must have just happened. Damage is fresh and all the others are fine.

Maybe the thinner one here was also on an intake and last time i did them it ended up on an exhaust valve.

Ive checked/set my tappets 3 times and every time they were pretty much spot on already.

As i say though, i dont know these engines so i may be missing something in my diagnosis.

[Bob Wessner]

As far as I know, the tappet covers are interchangeable on any given bike/model. Could be wrong, but...they are all the same, denominationally, on my 750.

[graeme7]

The differences are minor, you wouldnt know unless you took them off and checked.

Holding 2 side by side you can see some are slightly thicker and deeper than others. Both flat on a table the overall height difference is about 0.8mm or so.

I also wondered if there were ever any origional looking copies made over the years.
They dont seem different enough to cause a problem, but maybe they are?

[Bob Wessner]

Interesting. Now I'm curious. [heads for garage]. 

[graeme7]

Here you go, (bad) comparison pic.

I have 7 thick and 5 thin.

They are 2 distinct sizes.



But, would this be enough for an adjuster to clip it?

[graeme7]

Just to clarify, i doubt inlet and exhaust would be different, im wondering if they changed over the years, or between different capacity CB's.

I may have a mixed set.

I am wondering though if the exhaust side might need more clearance than the inlet.


Im just concerned about why its clipped! Dont want to pull the motor to remove the cover so i can check, but dont want to ride it if there could be a problem.

I assume any issues with the rocker gear would show up when adjusting, or sound like a bag of spanners when running.

[MCRider]

Seems like 2 parts with that much difference would carry different part numbers. While i haven't seen them all, all I have seen carry the same part number, leaving us with the question, which is the "wrong" part. Maybe an aftermarket non-OEM replacement.

I can't imagine any CB750 engine cliipping a OEM tappet cover under any circumstance other than the nut actually coming off. Once the get loose they don't retighten themselves.

You've got an interesting problem.

[graeme7]

The damage looks fresh.

I guess my next stage is to re-fit the covers, ride it again and see if the noise persists.

It didnt quite sound like a loose tapped, sort of half way between a loose tapped and a really bad constant case of pre-ignition.

It was too constant for pinking though, and not consistand enough in the timing of its repetition to have been a loose tappet.

Ill run it, take the covers of again (this time making a note of which hole they came from) and inspect for more damage.

On a seperate note i might need to take the head of anyway. When turning the engine over with the kickstart to get to TDC i can hear a hiss as the compression leaks away (through the inlet valves i think).

I assume there should be no compression leak hiss at all?

Thats a seperate issue though.

[graeme7]

Also, just so you guys know, with the valve fully closed every adjuster sticks about 2mm out of the hole in the cover. Every adjuster looks the same with no thread showing above the nut, just the head of the adjuster screw (3mm or so above the nut).

Ive no idea why this damm thing is clipping the cover 

[graeme7]

I fitted all the thicker covers, put the only thin one i had to use on an inlet.

Took it for a 5 min ride and it seems fine.

Ill ride it harder tomorrow, get it reving out fully, then take all the covers of again to make sure.

Wierd issue, but looks like its solved, even if i dont ever find out exactly what happened.

[Old Scrambler]

I noticed this same issue on my K3 motor with about 70,000 miles of wear...........The intake seat on #1 was worn and allowd the valve to sink deeper into the head.  When I reassembled the motor with new seats and valves, I had a 'ticking' sound and found it to be an adjuster hitting the intake cap on #3.  I installed a new o-ring on top of an old 'squished' unit and all is well.

[graeme7]

That thought had crossed my mind.

If it had significant valve seat regression i'd expect to see that reflected in the adjuster possition.

I dont know how tight the clearances in there are though.

Had a good run on it today, took caps off, and i can see no evidence of clipping.

It still has a slight tappet noise, only occurs at steady RPM or accelerating, goes away when you let the throttle off.

Might just be hearing the tappets working though as all clearances are spot on.

[754]

 A few things. ;
 Those covers were produced for at least a 20 year period, and maybe by more than 1 vendor.
 If for example the drawing spec was = or - .5mm, then Both those covers could be within acceptable specs.
 If some 750 cams have say .400 lift (and some do), then I would suggest there is at least 2mm clearance on a stock cam.
 I will post a POSSIBLE SCENARIO, dont take this as gospel.. A newby adusts the valves on wrong cylinder, starts it up to excesssive clatter , then sets it back to correct.... but now it has kissed the cover. The cover, being protected from elements and not prone to corrosion.. looks the same way..4ever, and ever, and ever.. much like blued pipes.. cant tell if it just happened or was a decade ago..

 That is one POSSIBLE scenario.. if they are hitting now, you WILL probably hear it...
 NEXT if you REALLY WANT HELP, state your location.. help may be 4 blocks away.. and listing model of bike( I know you did) is never a BAD thing...
 Good Luck...

[xsmooth69x]

i had a problems with my tappets and it made marks on the caps

http://forums.sohc4.net/index.php?topic=91851.msg1025631#msg1025631

thats my thread

figured out that the rods holding my tappets started to wear away in the cover making it sloppy



good



bad



but this is off a 1975 cb550

you did hear the tappets hitting the covers though so if the marks are fresh you should hear them hit

next time though hit the macro button on your camera. its usually the flower symbol so you can shoot pics really close to something.

also although the actual height of the covers are different the distance from the  bottom of the threads up to the bottom base look like the same height. the only difference is the actual cap thickness.

[bryanj]

Pattern tappet covers, not only Honda supplied them as it was common to have to replace 2 or more every service, especialy if the owner had "tweaked" them with an open end spanner!!

[fastbroshi]

  The cover, being protected from elements and not prone to corrosion.. looks the same way..4ever, and ever, and ever.. much like blued pipes.. cant tell if it just happened or was a decade ago..

 This was my exact thought when you described the damage as "fresh".  The aluminum, being constantly covered in oil mist wouldn't hardly oxidize, if at all.  So it might've been done once when a newb adjusted the valves, or if an adjuster was temporarily loosened excessively. 

  And the problem xmooth posted pictures of didn't happen to any of the 750s that I was aware of.  It was just a problem on the early model 550s (maybe the 500s too?). 

  OldScrambler, I was thinking of what you said.  If a valve had sunken in its seat, this would make the valve tip protrude farther out and possibly contact the tappet cover and make some racket.   You said the noise persisted after the seats were recut.  I'm sure the machinist cut the correct amount of metal to make the new seat too.   I wonder just how much is cut in this process normally?  How many miles were on that motor?

[graeme7]

I hadnt thought it could be old damage, good point.

As for the comparison pic, yes, the threaded portion to the seating lip is the same length. Its just the overall height and therefore internal depth that differs.

Thats where mine was hitting, not on the lip like yours.

Ive done about another 100 miles since this and it still has a slight tappet noise. Re-checked them and there fine!

I think there may be something else that sounds pretty much like a slightly loose tapped.

Any ideas?

[bryanj]

exhaust gasket blow can sound like a loose tappet

[graeme7]

Thats interesting, i had wondered.

Ive had the exhaust off recently and not replaced the gaskets. It does seem to be a little louder when hot, maybe it starts to leak more then.

I need to order some more bits and new exhaust gaskets are on the list so maybe ill be lucky.

Ill report back next week when ive finished rebuilding the front end.

Thanks.