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SOHC.co.uk Forums => CB500/550 => Topic started by: paulbaker1954 on September 09, 2019, 06:13:44 PM

Title: Running like a dog Part II
Post by: paulbaker1954 on September 09, 2019, 06:13:44 PM
Starting a new thread as things have changed

Had bike at local mechanic who is convinced the afterfiring on 1 and 2 is being caused by a valve issue.

So I am going to pull the head again but could use some help with steps or procedures I should work through to to check this out

I did do a compression test and this seemed ok but my mechanic said really need to do a leakdown test but problem is I don’t have a compressor. He also said that only sure way to do a leakdown anyway is to take the tapper cover off so nothing is pressing the valves
Title: Re: Running like a dog Part II
Post by: K2-K6 on September 09, 2019, 09:37:30 PM
I don't think I understand his reasoning regarding removal of rockers.  T mark on timing will give closed valves on compression stroke for whichever cylinder to be tested. That's assuming your valve clearances verify as ok.

Out of interest what compression psi figures do you have for each cylinder? That should give you a reasonable assessment to proceed with at least.

I'd have thought it's worth checking now to have a record of how it is right before you do any further work on it.
You're looking for 170 psi as ideal two start with.
Did you also test with light oil in each cylinder after taking a dry reading too? So you'll have two figures for each cylinder.
Title: Re: Running like a dog Part II
Post by: paulbaker1954 on September 10, 2019, 08:44:45 AM
I agree about your thoughts that his reasoning is off. AS you say as long as piston is at TDC and there is some slack in the tappet adjusters then that is all you should need for a leak down test.

In any case the mechanic seems very reluctant to take on my bike as he says he is so busy (my thought is he just doesn't want the hassle of taking the project on and he only likes working on more modern injection bikes). That said he is an experienced guy who does a lot of race bike prep and he is clear that he has heard and seen this type of issue associated with valve problems

As to compression test I got a uniform 135 psi across all 4 pots when cold and dry and went up to around 170 with oil in bores. I am not bothered about the 135 reading as there are theories around about why Honda say 170 that are down to using cheaper flexible hose compression testers.

So the compression seems to check out OK so why this damn poor running and after fire.

I decided to go right back to basics and what has changed since it was running well. What has changed is that I changed the Head Gasket and this is when this all started.

So my questions/comments

1) What could I have done (all stupidity included) in the head gasket change that could have damaged/done something to the valves?
2) The afterfire does not happen until the bike gets warm. In fact on first start and off the line seems to be running really well then as the engine gets warmer things just get progressively worse. So the problem is down to something expanding as things get hotter.
3) What is the best attack plan to try and identify a vale issue that gets worse as things warm up?
4) As I am very time limited does anyone know of someone who could fix this for me in the Warrington area?
Title: Re: Running like a dog Part II
Post by: hairygit on September 10, 2019, 08:54:54 AM
You may have fractionally bent some valves, probably exhaust ones given the after fire in the pipes, and as the calves heat up the stems expand a fraction, but enough to cause intermittent sticking. That is only a theory, but knowing how easy it is to damage valves fitting the rockers in the 350/400/500 and 550 fours, it certainly warrants further investigation if the head is coming off again. The affected valve seats may show signs of burning as a result, but not much as it has not been ridden much since this started

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Title: Re: Running like a dog Part II
Post by: paulbaker1954 on September 10, 2019, 09:00:37 AM
You may have fractionally bent some valves, probably exhaust ones given the after fire in the pipes, and as the calves heat up the stems expand a fraction, but enough to cause intermittent sticking. That is only a theory, but knowing how easy it is to damage valves fitting the rockers in the 350/400/500 and 550 fours, it certainly warrants further investigation if the head is coming off again. The affected valve seats may show signs of burning as a result, but not much as it has not been ridden much since this started

Sent from my POT-LX1 using Tapatalk

Thanks Hairy useful input, one question is you say how easy it is to damage the valves etc. What are the big care points when refitting. May be some clue as to what I have done !!

Also what do you mean by valve "calves"???
Title: Re: Running like a dog Part II
Post by: K2-K6 on September 10, 2019, 09:28:32 AM
Agree with HG regarding potential of valve damage and your mechanic guy.

As said above,  if you are taking the head off anyway it'll obviate the need to complete leak down testing.  Just support head upside down and fill each combustion chamber with choice of petrol / Paraffin / isopropyl alcohol and it'll leak out down through the port if it's not sealing properly.

Are those compression values after this build or prior to it? Raising psi with oil is usually considered to improve piston ring sealing generally and not valves which logic is used to seperate the two fault areas. As you indicate,  your stated figures don't initially point to a valve problem.

Warm up has different combustion mix than hot which is generally much easier to burn,  coming off richer running to optimum is more likely to show error as it's less tolerant of combustion inaccuracies.  This is potentially a change that you see rather than a mechanical shift due to heat.

If we make a statement of fault "it's burning something in the exhaust post combustion chamber" then work up potential from there it shows options to consider.

If you switch off while running down hill in gear,  open throttle and the switch back on again,  the exhaust will backfire.  That's one way of producing the effect by way of demonstration of principle as you've actively passed unburnt combustible mixture through the cylinders into exhaust.

So,  with a bent valve,  it could have reduced compression and pass partly burnt mixture (incomplete burn will change depending on mixture)  down exhaust port.  Not much in volume but accumulating until it reaches critical condition to explode,  giving you the symptoms you get.
Hotter combustion temp will just set off backfire more easily than choke running,  which could give you the change you see from engine temperature.
Title: Re: Running like a dog Part II
Post by: hairygit on September 10, 2019, 09:59:30 AM
You may have fractionally bent some valves, probably exhaust ones given the after fire in the pipes, and as the calves heat up the stems expand a fraction, but enough to cause intermittent sticking. That is only a theory, but knowing how easy it is to damage valves fitting the rockers in the 350/400/500 and 550 fours, it certainly warrants further investigation if the head is coming off again. The affected valve seats may show signs of burning as a result, but not much as it has not been ridden much since this started

Sent from my POT-LX1 using Tapatalk

Thanks Hairy useful input, one question is you say how easy it is to damage the valves etc. What are the big care points when refitting. May be some clue as to what I have done !!

Also what do you mean by valve "calves"???
Sorry, bloody auto correct crap that I can't turn off in Tapatalk, it should have said as the VALVES get warm and expand, the stems start sticking in the guides.

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Title: Re: Running like a dog Part II
Post by: paulbaker1954 on September 10, 2019, 10:02:34 AM
You may have fractionally bent some valves, probably exhaust ones given the after fire in the pipes, and as the calves heat up the stems expand a fraction, but enough to cause intermittent sticking. That is only a theory, but knowing how easy it is to damage valves fitting the rockers in the 350/400/500 and 550 fours, it certainly warrants further investigation if the head is coming off again. The affected valve seats may show signs of burning as a result, but not much as it has not been ridden much since this started

Sent from my POT-LX1 using Tapatalk

Thanks Hairy useful input, one question is you say how easy it is to damage the valves etc. What are the big care points when refitting. May be some clue as to what I have done !!

Also what do you mean by valve "calves"???
Sorry, bloody auto correct crap that I can't turn off in Tapatalk, it should have said as the VALVES get warm and expand, the stems start sticking in the guides.

Sent from my POT-LX1 using Tapatalk

HA HA I get some really crazy auto corrects

Anyway what is the the correct/safe procedure for putting tappet cover back on. I know about the elastic band trick but anything else to watch for
Title: Re: Running like a dog Part II
Post by: hairygit on September 10, 2019, 10:21:50 AM
Ensure ALL tappets are slacked off and wound out as far as they will go, the problems occur when a tappet depresses a valve as the rocker cover is tightened down, and the pressure results in bending the valve stem.

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Title: Re: Running like a dog Part II
Post by: hairygit on September 10, 2019, 01:03:58 PM
I find it much easier when trying to source a valve seat leak to fill the tract up with petrol rather than the combustion chamber, you get more in and it's far easier to see the leakage as you can look directly at the valve seat whilst it's trying to leak past. This was how I lapped valves in, I'd just hold the stem with a tap wrench and see if any petrol leaked past, if the seals good it wouldn't leak past even with lower pressure exerted on the valve seat. I liked using petrol as it was easy to obtain and it was very easy to spot as it leaked past.
   In most situations I would 100% agree on that one Oddjob, but if the stem is fractionally bent, so little that it only gets sticky when the stem is at running temperature, it may not have damaged the seat enough to see any leakage. Also, if the bend is so minor it probably wouldn't show lapping valves in if there is any clearance in the guides.
Title: Re: Running like a dog Part II
Post by: paulbaker1954 on September 10, 2019, 01:18:02 PM
I find it much easier when trying to source a valve seat leak to fill the tract up with petrol rather than the combustion chamber, you get more in and it's far easier to see the leakage as you can look directly at the valve seat whilst it's trying to leak past. This was how I lapped valves in, I'd just hold the stem with a tap wrench and see if any petrol leaked past, if the seals good it wouldn't leak past even with lower pressure exerted on the valve seat. I liked using petrol as it was easy to obtain and it was very easy to spot as it leaked past.
   In most situations I would 100% agree on that one Oddjob, but if the stem is fractionally bent, so little that it only gets sticky when the stem is at running temperature, it may not have damaged the seat enough to see any leakage. Also, if the bend is so minor it probably wouldn't show lapping valves in if there is any clearance in the guides.

Hairy i tend to agree on this point. I think this is why a compression test is fine because the valves are sticking when they warm up a bit.

I am going to pull the head and take whole head complete with valves to my local machine shop who are really good and have them check clearance, straightness etc. They are very good and have all the right measuring kit

We will see !! I have exhausted pretty much all other possibilities and looking back all this started when I replaced the head gasket. Given that valve timing is right for sure and tappet clearances are OK.................
Title: Re: Running like a dog Part II
Post by: Rob62 on September 10, 2019, 01:25:24 PM
For what its worth, my advice would be to strip the head and barrels, start with new gaskets / seals and thoroughly inspect all the components, valves, pistons, rings etc as they are refitted, get the head checked for cracks / warpage etc.

Since you don't have a specific diagnosis there is no specific cure, so stripping and rebuilding is probably the only way forward and provides an opportunity to check everything is within spec when refitting... you will hopefully find something and cure the issue. And if you are mechanically competent you can do it yourself and save money as these engines are not high tech...

Good luck with it.. hopefully you will solve it soon.
Title: Re: Running like a dog Part II
Post by: paulbaker1954 on September 10, 2019, 01:45:34 PM
Paul, by any chance did you take the bike to Hammer and Tongs in Warrington?

For some reason I'm not convinced the valves are the problem, not sure why, just a gut feeling, something in my head keeps saying it's a gasket problem, again, I'm not sure why but I can't shut the damned voice in my head up.

I'll be happy if it is a valve problem, at least then I can tell the voice to shut the hell up and stop bothering me.

Am I going mad? it's a possibility.  ;D ;D

No -- I went to IFS engineering in Lymm (Iain Sutton) bit grumpy but seems pretty on the ball. He is convinced it's valves
Title: Re: Running like a dog Part II
Post by: Nurse Julie on September 10, 2019, 01:50:50 PM
Oh dear Paul....you have done well so far retaining your sanity over this problem 😀 Did you back off the tappets fully and hold the tappets up with elastic bands when you fitted the rocker cover?
Title: Re: Running like a dog Part II
Post by: paulbaker1954 on September 10, 2019, 02:02:14 PM
Oh dear Paul....you have done well so far retaining your sanity over this problem 😀 Did you back off the tappets fully and hold the tappets up with elastic bands when you fitted the rocker cover?

Hi Julie
Yes this is doing my head in !!!

Thinking back when I put the cover back on it was a struggle to get on, I backed off the tappets but no lazzy bands. Cover seemed to be offering some "push" resistance. I am now thinking this is what caused the problem but I guess will only know when I get the head off AGAIN and get the valves checked out. Head is off to my local machine shop with valves in for them to check it all out (they are very good)
Title: Re: Running like a dog Part II
Post by: Nurse Julie on September 10, 2019, 02:18:56 PM
Oh dear Paul....you have done well so far retaining your sanity over this problem 😀 Did you back off the tappets fully and hold the tappets up with elastic bands when you fitted the rocker cover?

Hi Julie
Yes this is doing my head in !!!

Thinking back when I put the cover back on it was a struggle to get on, I backed off the tappets but no lazzy bands. Cover seemed to be offering some "push" resistance. I am now thinking this is what caused the problem but I guess will only know when I get the head off AGAIN and get the valves checked out. Head is off to my local machine shop with valves in for them to check it all out (they are very good)
Great, I hope they find the problem for you. It's strange because in the 400/550 Haynes manual they make no mention of pulling the tappets up and securing them (can't remember if it actually says elastic bands or not) before refitting the rocker cover but it definitely shows a picture and explains it in the 500 manual 🤔 I'm not sure if it shows this way in the 750 manual, can't remember at the moment. I know Trig ties them all up with laccy bands on all engines  to prevent damage to the valves whilst bolting the rocker cover down in sequence.
Title: Re: Running like a dog Part II
Post by: hairygit on September 10, 2019, 02:43:59 PM
Not in the 750 manual Nursey, separate rocker cover, the tappets/rockers are mounted on the cam carriers.
Title: Re: Running like a dog Part II
Post by: Nurse Julie on September 10, 2019, 02:47:17 PM
Not in the 750 manual Nursey, separate rocker cover, the tappets/rockers are mounted on the cam carriers.
Yep, indeed you are correct Mr Hairy....and thats exactly word for word what Trig has just told me 🙄🙄🙄🙄 Its the Cypriot beer and the sun, I'm brainwashed ....and bloody lovely it is too, being brainwashed that is 🤣🤣🤣🤣
Title: Re: Running like a dog Part II
Post by: K2-K6 on September 10, 2019, 02:54:30 PM
The 750 has the rockers etc fully installed prior to cam cover being fitted so the scenario doesn't occur on that, just the smaller capacity fours which are all the same.

Out of interest, what do the rockers catch on if you leave them unelasticated?  I understand the process of fitting them but not the precise layout that would give some sort of interference.

It's highly unlikely that you bend a valve stem like this I'd guess.  They are just very tough to bend at the top end of valve.

But,  if you left the engine at TDC for number one cylinder for example, could you then get a situation in which you pushed the valve down into the top of the piston from "snagging" the rocker arm as you close the rocker cover gasket.  Ie, exactly what you are trying to avoid by using elastic to keep the rockers up.
If you can do that, then it's more likely to bend the valve using the head as leverage against the piston.

If that's a viable scenario,  then it would most likely be #1 cylinder in all probability if you've just checked cam timing is correct before you install cover. And I'd have a guess at exhaust on that cylinder.
Title: Re: Running like a dog Part II
Post by: paulbaker1954 on September 10, 2019, 03:03:49 PM
The 750 has the rockers etc fully installed prior to cam cover being fitted so the scenario doesn't occur on that, just the smaller capacity fours which are all the same.

Out of interest, what do the rockers catch on if you leave them unelasticated?  I understand the process of fitting them but not the precise layout that would give some sort of interference.

It's highly unlikely that you bend a valve stem like this I'd guess.  They are just very tough to bend at the top end of valve.

But,  if you left the engine at TDC for number one cylinder for example, could you then get a situation in which you pushed the valve down into the top of the piston from "snagging" the rocker arm as you close the rocker cover gasket.  Ie, exactly what you are trying to avoid by using elastic to keep the rockers up.
If you can do that, then it's more likely to bend the valve using the head as leverage against the piston.

If that's a viable scenario,  then it would most likely be #1 cylinder in all probability if you've just checked cam timing is correct before you install cover. And I'd have a guess at exhaust on that cylinder.

Here is the picture from the Honda manual, I think I can see that if you end up with a rocker in that sort of position its not hard to bend a valve maybe


[attachimg=1]
Title: Re: Running like a dog Part II
Post by: Nurse Julie on September 10, 2019, 03:24:50 PM
The 750 has the rockers etc fully installed prior to cam cover being fitted so the scenario doesn't occur on that, just the smaller capacity fours which are all the same.

Out of interest, what do the rockers catch on if you leave them unelasticated?  I understand the process of fitting them but not the precise layout that would give some sort of interference.

It's highly unlikely that you bend a valve stem like this I'd guess.  They are just very tough to bend at the top end of valve.

But,  if you left the engine at TDC for number one cylinder for example, could you then get a situation in which you pushed the valve down into the top of the piston from "snagging" the rocker arm as you close the rocker cover gasket.  Ie, exactly what you are trying to avoid by using elastic to keep the rockers up.
If you can do that, then it's more likely to bend the valve using the head as leverage against the piston.

If that's a viable scenario,  then it would most likely be #1 cylinder in all probability if you've just checked cam timing is correct before you install cover. And I'd have a guess at exhaust on that cylinder.

Here is the picture from the Honda manual, I think I can see that if you end up with a rocker in that sort of position its not hard to bend a valve maybe


(Attachment Link)
That is exactly the position, with the tappet touching just the very side of the top of the valve stem when tightening down the rocker cover, that causes bent valves. That's why the manual puts huge importance on making sure they are not touching so as to prevent bent valves.
Edit...sometimes you are given a warning that things are not right by the threads stripping when trying to do up the bolts as there is too much resistance and either the thread will strip first or if not, then the valve bend. Something has got to give if the tappet is touching the valve in the wrong place.
Title: Re: Running like a dog Part II
Post by: matthewmosse on September 10, 2019, 07:47:22 PM
One of mine gave a clear sighn this was the issue, the tappet and top of valve both went blue with heat discoloration. To ride it was ok for maybe a mile, then rough as a badgers rear end. Was mostly ok again if allowed to cool.  That engine still sat in a corner someplace. If that's the problem I geuus the effected valve and guide need replacement. Should be easy enough to spot by rolling the valve stem along glass and testing if a feeler gauge can slip under it at various points as its rolled. Is it viable to ream a valve stem rather than replace and then ream the new one? Probably not.

Guy I bought my first 550/4 from said he had on some bikes stereightened valves that had bent when camchains had let go and got the bikes going again, but given the dammage a dropped valve can do it's a step too far even for me.
Title: Re: Running like a dog Part II
Post by: K2-K6 on September 10, 2019, 08:43:18 PM
This has made me laugh,  I clipped it to remind me of what some do inside engines.

[attachimg=1]

Looks like it's been running a while too  ;D

Title: Re: Running like a dog Part II
Post by: Erny on September 10, 2019, 09:23:15 PM
 ;D ;D ;D ;D
never seen such "repair"
But can imagine, somewhere in the middle of nowhere in the past (no spares avail) that can fix issue ;)

I still remember in communist times in Czechoslovakia, some guys fixing rod's bearings with layers of aluminium foil - and it was working quite well for some time
Title: Re: Running like a dog Part II
Post by: matthewmosse on September 11, 2019, 02:15:03 PM
Is that what I think it is? A plate screwed to the top of a piston? I have seen it before but what a bodge. Kind of thing some of my mates used to attempt. Amazing how long an engines will last with sutch ' repairs' I had a dumper engine once that had obviously run some considerable time with a piston top knocking around in the combustion chamber, long enough for the exhaust port to be chocked with carbon build up til the ports were pencil sized holes. Other cylinder was fine, it would probably still have run.....
Title: Re: Running like a dog Part II
Post by: paulbaker1954 on September 11, 2019, 03:20:49 PM
Is that what I think it is? A plate screwed to the top of a piston? I have seen it before but what a bodge. Kind of thing some of my mates used to attempt. Amazing how long an engines will last with sutch ' repairs' I had a dumper engine once that had obviously run some considerable time with a piston top knocking around in the combustion chamber, long enough for the exhaust port to be chocked with carbon build up til the ports were pencil sized holes. Other cylinder was fine, it would probably still have run.....

I was trying to work out what it was - unbelievable !!!
Title: Re: Running like a dog Part II
Post by: K2-K6 on September 11, 2019, 03:34:50 PM
Yes,  top of piston #3 watercooled 750 Suzuki triple.

You'd have to say it's inventive  ;D at a guess.
Title: Re: Running like a dog Part II
Post by: paulbaker1954 on September 13, 2019, 10:44:48 PM
Ok head off AGAIN and checked valve leakage by putting petrol in combustion space-no leakage but I am guessing that if it was top of stem that got bent putting cover back on that would be expected as the bend would be above the guide (opinions please).

Taking head to local machine shop for valve check and overhaul next week so will know more then
Title: Re: Running like a dog Part II
Post by: matthewmosse on September 14, 2019, 12:51:49 PM
If you can remove the valve cap and see if it comes out freely that might be a good first indication. Depends on having the right tool to get the collects out though. Possible without correct tools but can be a fight.
Title: Re: Running like a dog Part II
Post by: matthewmosse on September 15, 2019, 09:35:06 AM
Dab of grease on them to refit too. Its compressing those valve springs that's hard work without the right tool, a bit of gp100 for stanchion with hacksawed slots to give access and a G clamp was what I resorted to last time. What has held me back from going near the job again is having the confidence to assess the guides condition, it's one thing for them to slide freely by hand without excess play but that might not translate to smooth operation at 9,000 rpm. I have one cb500/4 engine I rebuilt from several scrap ones that has this issue.
Title: Re: Running like a dog Part II
Post by: paulbaker1954 on September 16, 2019, 08:35:45 AM
Paul I have the genuine Honda spring compressor for getting the valve springs out. I can pop round after work one night and we can get them removed within around 10 mins if you'd like. It would be around 8.45pm though.

Hi Ken
Thats a very kind offer but I am going to drop head off at my local machine shop for them to do the work as am going to use the opportunity to have all checked, valves reground in etc whilst head is off

I think better to get valves professionally checked rather that rolling them around on glass as I suspect the bend if there is may be only slight but enough to cause them to stick when warm.

Title: Re: Running like a dog Part II
Post by: paulbaker1954 on September 20, 2019, 07:18:13 AM
Paul I have the genuine Honda spring compressor for getting the valve springs out. I can pop round after work one night and we can get them removed within around 10 mins if you'd like. It would be around 8.45pm though.

Hi Ken
Thats a very kind offer but I am going to drop head off at my local machine shop for them to do the work as am going to use the opportunity to have all checked, valves reground in etc whilst head is off

I think better to get valves professionally checked rather that rolling them around on glass as I suspect the bend if there is may be only slight but enough to cause them to stick when warm.

Welll just my luck!!!!!!

 machine shop called me yesterday all the valves are good and no bends anywhere in sight

Having head skimmed and valves lapped in anyway whilst it’s there but......

That means still no nearer finding the cause of my running problems and think I have exhausted all things to check

This is soooooooooooooo frustrating!!!!!!!

I have now checked and tested the following.....
Carbs stripped and idle circuits checked, no pilots blocked
Good even compression on all 4 cylinders
Complete ignition system back to Boyer for testing and no issues
Leads and plug caps tested and all ok
Valves checked for any bends, leaks etc -all good

Am really now clutching at straws but have one final theory

I put  2 small lengths of nitrile fuel tubing on the tank petcock and connected these using 2 right angle elbows to the carb hoses. I cannot see any kinks in the tubes when installed that would cause a fuel cut off to carbs 1 and 2 but is it possible that by using these right angle connectors that I am somehow upsetting the fuel flow as they have a smaller bore than the hose of course

[attach=1]

See my other post today about petcock behaviour

This may sound crazy but I am now really clutching at straws. I seem to remember a post from another member about these bikes being very fussy about hose routing and dimensions

Whilst all is apart am going to get rid of these connectors and put some new hose direct from carbs to petcock to eliminate this as a possible cause
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