Top-end noises....

[ScottishBadger]

Folks.
I've removed my cam cover and started trying to trace this noise..... If anyone has ever heard an old GM OHV engine with a slack rocker arm, that's what it sounded like - a proper "clack-clack-clack", audible with my helmet on!
All valve clearances have been checked - a few are too tight, a few are a bit loose, most are around 0.0035" to 0.0045" which is reasonable. None are excessive, which is a good thing I suppose. (widest clearance is one of the no.1 inlet valves, at 0.007")
Both cam chains were tensioned ok, with no slack or backlash in the chains.
I've removed the left inlet cam as that's where the noise seemed to be coming from (around no.3) - the Oldham Coupler slid out freely on its own, but there is absolutely no measurable play between coupler and cams.....
The tappets themselves are not slack in the head casting and they slide freely.
All cam bearings checked so far appear absolutely perfect with no indication of wear, but I will plastigauge them to be sure.

Unfortunately, when I bought this bike it had a Delkevic 6-into-1 exhaust on it, it was so loud you'd never have heard anything else! It was only when I fitted the supplied original exhausts that I started to hear things.....

[herdygerdy]

Sorry to put this to you ScottishBadger, but it is entirely possible it may have a bent rod.

If it does, it is likely the noise you are hearing, most likely from below the cylinder head, somewhere around the back of the barrels on the LH side of the engine (i.e., around cyls 1-3) is the bottom edge of the skirt of the piston 'kissing' (or in extreme cases 'slapping') the crankshaft webs as that cylinder rotates around BDC.

You may also observe lots of fine alloy particles in the oil when looked at in the Sun.

Use the extended centre tang of a vernier caliper to carefully measure from the top of the plug hole down the bore and onto the top of the piston crown as it is SLOWLY rotated over TDC (best done with a friend).

Measure and record that number for all 6 cylinders. All six 'should' be somewhere in the order of 27.4 mm, subject to the amount of carbon that may be on the crown of the piston.

If any number for a cylinder is significantly GREATER than around 27.4mm, that means that piston is not rising as far as the others and so that is the one that will most probably have a bent rod.

Another option is to do a compression test. if any cylinder is significantly lower than the others, that is most likely the one with a bent rod.

Only way to be sure is to pull the engine and dive in.

Let us know how you go and good luck.

[512tr]

You've probably checked..... a exhaust header leak (missing or insufficient exhaust gasket/ring) can sound like a terrible top-end noise.

[ScottishBadger]

herdygerdy, I will pull all the plugs tomorrow and check - in my mind I'm saying check to eliminate, as the noise is definitely top-end not down the back of the barrels. I've already done an oil change, the oil came out clean and the old filter was also clean with no particles in it (I always check filters on bikes when I renew them!). It pulled like a train right up to the redline, I'd have thought that would have provoked a bent rod to throw....? There's no untoward vibration or roughness either.
I plastigauged the cam bearings today - Journals 9 and 11 were at 0.002", journal 10 at 0.003" and journal 12 is 0.0015", so there's nothing untoward there. One thing I did discover was the left inlet valve on cylinder 1 had around 0.007" clearance yet it had a shim way bigger than every other valve, a 3.05mm shim when everything else is between 2.82 and 2.92. On investigation, the raised portion inside the tappet that contacts the top of the valve stem has considerable uneven wear - yet the valve stem itself is perfect, thankfully! Looks like I'm looking for a tappet bucket now as well, but it wasn't the source of my noise, as there was no abnormal noise from near that end of the rocker cover, only the area immediately adjacent to the left of the cam chains, above no.3...

512tr - no leaks, all brand new gaskets, nuts and studs when I took the Delkevic off and put the original exhausts on.

[herdygerdy]

OK, well that sounds hopeful ScottishBadger.

Is it possible the pinch bolt at the front of the cylinder head that secures the shaft of the B tensioner (for the small chain driving the inlet cam from the exhaust cam) has the thread for the bolt stripped in the head? If that pinch bolt comes loose, then the B chain beats mercilessly onto the tensioner which is now free to flap up and down. This causes both the tensioner and potentially the cam chain to wear prematurely.

Did the tensioners look OK when you had the left inlet cam out?

Is it possible you've got the cam timing wrong when you put the cam(s) back in? You know it is right when cam lobes for, say the inlet cam, on cylinder no. 1 are facing TOWARDS the spark plug then the lobes for cyl. no 6 MUST be 180 degrees opposite, facing AWAY from the spark plug.

Clutching at straws a bit now...

[ScottishBadger]

Hi herdygerdy.
I've pulled the plugs and taken measurements as you advised, readings (in mm) as follows:-
1 - 28.34
2 - 28.68
3 - 28.51
4 - 28.48
5 - 28.70
6 - 28.37
I'd say my depth gauge was about 4 to 5 degrees off perpendicular on cylinders 2 and 5 due to the frame rails being in the way, so I would make a very slight allowance (basic trig suggests roughly 0.08mm), which puts them all within a 0.28mm range.
Allowing for any tolerances due to carbon, plug seating face depths etc etc, I'm pretty confident with these numbers that there's no bent connecting-rod, unless of course all six are bent by an almost identical degree....... let's not go there

The B tensioner lockbolt does indeed pinch correctly on the rod and secure it, the chain cannot be depressed without undoing that bolt. Same for the main A tensioner, it is free and operating correctly and is secure when the dome nut is tightened. The engine has not been fully re-assembled since I started investigating this, and it was running nice on all 6 (bar the noise!) before I took it apart. The left inlet cam has to come back out to replace the worn bucket (1A Inlet) once it arrives, but the cam timing is indeed correct and the bolts on the sprocket are tight as well.

I think it's going to have to be a case of put it back together with new Oldhams, re-shim everything and see where we go from there.....

[herdygerdy]

OK, SB, you're clearly all over this and the measurement of piston crown heights all being within a range of 0.36mm suggests all is in order, err, 'down there'. Phew! (variation
Also what you've described wrt the operation of the cam chain tensioners and securing bolts all sounds in order. Just one thing more to verify is the relation of each camshaft half in relation to each other. The LH (exhaust, for example) camshaft 'half' needs to be 180 degrees from the RH half. Ditto for the inlet camshaft LH and RH pairs. But ack you've probably got this right, but I had to ask (assumption is the mother of all stuff-ups)

So, where to next? Is it possible you may be getting bad pinging or detonation due to incorrectly set up ignition timing? Does it have OEM ignition that is set correctly or an aftermarket one? In my experience Dyna can be problematic if not fitted and set up correctly. Maybe worth pulling the auto-advance unit to check that is working correctly and all springs are good and it is returning freely to rest.
How many kms on the bike? Has engine been apart? While that left inlet cam is out, check the 10mm mounting bolt of the small B tensioner deep in the camchain valley at the rear of the cyl. head. Is it there and tight?
Keep us posted.

[ScottishBadger]

Herdygerdy.
Cam relationship was (is) fine, she was running smooth on all six, just the noise was the problem.

I did a static check on the ignition (and made sure the advancer was free at the same time), however that wouldn't have caused pinking at idle and it wouldn't have been regular and rhythmic like the clack-clack noise I was getting.
Speedometer suggests 24,000 miles - but how accurate that can be is anyone's guess on a 43 year old bike, haha. Looking at the cams and followers, there is no wear on the lobes, all bearing surfaces are perfect and bearing clearances are good as well, so I think it's safe to say the mileage probably isn't intergallactic at least....
I took the right inlet cam and sprocket out and checked the bolt at the rear of the B tensioner as you suggested - I got about half a flat on it to re-torque it, but it certainly wasn't loose and there was no movement of the tensioner.
Whilst both inlet cams were out, I did a straight-edge check across all the inlet cam journals, all were perfectly in line using engineer's blue as a contact guide. I took the oppertunity to check the right inlet cam bearing clearances at the same time, again using plastigauge after pulling all the buckets out so there was no force on the cam whilst doing so. All were good.

I've also been trying to "think outside the box" with this one, and started considering valve springs. I can see enough of the outers using a small mobile-phone flexible borescope tool with the buckets removed to see there's no breaks, but I can't see the inners. So, I rigged up an extremely "heath robinson" pressure tester using another spring (XL500s inner valve spring!) and a small ruler, I did 4 valves on the engine, No.1 inlets and No.3 inlets (the suspects!), I noted the measurement on the ruler for the compressed length of the XL spring when each inlet valve had been depressed by 5mm, this hopefully was going to give me an indication if one valve was easier to open than the others, possibly indicating low spring pressure due to a broken spring somewhere. Again, I drew a blank, all 4 took the same force (compressed length) to move the valves by 5mm.

I think I've exhausted almost every possibility that can be checked now, without removing the head. I have ordered shims and will reassemble her, aiming for 0.10 - 0.11mm exhaust side and 0.08 - 0.09mm inlet side. I shall also stick in a set of the oversized Oldham Couplers, as I am happy the cam alignment is good, so fitting them won't cause any issues.

I will update again once I have the shims and get her back together.

[herdygerdy]

Thanks for the detailed update SB and TBH I'm running out of suggestions.

One thing you could do (and again, it's a long shot) is to check the primary chain for excessive wear. To do this pull the alternator out. Behind the alternator on the top crankcase half is a 10mm head bolt that secures an internal oil pipe that pokes inside the crankcase. Its job is to spray oil onto the primary chain as it goes round and round on its merry way.

When the alternator is removed a large opening in the crankcase is exposed. Be sure to immediately stuff a shop rag into the large hole. This will prevent 'things' dropping into the crankcase. DAMHIK! Only once the rag is in place, undo the bolt and withdraw the pipe.

If the primary chain is worn, or is not being tensioned properly due to low oil pressure in the tensioner, then the loose chain can 'flap' and so strikes the underside of the oil pipe as it whizzes by. if this is the case, then you will observe witness marks on the underside of that oil pipe.

Low oil pressure there could possibly caused by, for example, hardened seals on the primary chain tensioner or low pressure from the pump. Either would require you to open her up.

Others pls feel free to chime in with suggestions. It is a mystery SB, but your methodical approach is excellent. Rest assured we WILL prevail and we await your next update with interest.

[NobleHops]

I’m reading this incredibly thorough investigation, and about the only thing I can think of that might be unexplored is the A cam chain tensioner - if the plastic bow was busted, it could be flapping around in there making sinilar sounds.

[ScottishBadger]

Hi Nils, A-Tensioner examined visually using the mobile phone viewing probe, everything appears fine. Tensioner "snaps" into position when the locknut is loosened after it's been locked-off in the slackened position. Both chains are "tight" - if anything, my engineering experience is telling me they really don't need to be just quite as tight as they are in all honesty, but I'm trusting Honda's engineers on that one, plus I've never heard anyone say their chains were too tight!
The original noise was definitely 100% in sync with the engine speed and centred around the no.3 inlet valve area. I'm waiting on the oversized Oldaham Couplers arriving from the SixCenter, they were ordered and paid for last Friday and I was told I'd have tracking information Saturday, but so far I've not had that info....
I've gone as far as I can until the couplers arrive. Last night I shimmed all the valves of both right hand cams - No's 4,5 and 6 exhausts all absolutely spot-on 0.10mm, inlets at 0.08mm (with one "rogue" inlet valve at 0.09mm due to shim availability!). I have the shims all laid out for the left cams, I'll swap them over whilst the cams are out to do the Oldam Couplers.

[ericfreeman]

I noticed a rattling in the engine of my '79 when running below 4k RPM recently after the bike has been sitting all winter. Sounded like a knocking and I first thought about a rod. But then, I started thinking of other causes and the next time the noise came up I reached down and felt the alternator and behold, it is the source of the noise. Could be the clutch is chattering a bit at low engine speeds causing the noise. I can now sleep at night.

[Larry Zimmer]

thanks, Eric.

[ScottishBadger]

Okay folks, an update now that she's all back together.
Firstly, I decided to use only one oversize Oldham Coupler, on the inlet cams, as that was the area of the noise. I figured the exhaust had been quiet, so leave it alone!
I replaced all the shims according to my previous measurements and torqued everything up correctly. Then things went wrong......! I double-checked the valve clearances on cylindders 1, 2 and 3 and found they were all over the place, even the exhausts which hadn't been disturbed since initial measurement! Cut a long story short, I ended up re-shimming almost all of them another twice, until I was getting consistent measurements after turning the engine through 3 or 4 revolutions after each adjustment. I've now hit the limit of my stock of shims (and what seems available online) but all are within factory limits at least. I have erred towards caution, leaving a few slightly slacker than I'd like - in preference to being too close to their tighter limit, especially on the exhaust side.
I scrupulously cleaned the cam cover and glued the new seal in place - sparingly - with Hondabond and left it upside down with some books weighting down the seal into place overnight. The next day I installed the cam cover and put the rest of the bike back together..... and hit the starter button...
Basically, it still rattles, but nowhere near as much as it did previously. I now have slight "rustling" from both the valves on no.1 exhaust, 1B inlet and both no. 2 inlets - this is due to the larger clearances than I'd like, these valves are all around 0.12mm. The bad news - the new seal on the rocker cover was spewing oil out just in front of the no.1 inlets!!! Back apart, nothing found, eased the seal out of that end of the cam cover and put a straight-edge across the cam cover - it's got a very slight twist on the no.1 inlet end. Will my grief never end, I ask..... I also re-checked all the valve clearances on the left side yet again whilst the cover was back off and they seem to have remained at what they were set. The cam cover has been chromed at some point in the past, I wonder if that process could have somehow distorted it? Anyway, it went back together again, this time with a very thin smear of Hondabond on both sides of the seal, and I now have an oil-tight engine that doesn't sound like some little man is trying to break his way out with a hammer, haha.
I shall run it for a while, put a few hundred miles on it, them maybe pull the cam cover again and re-measure. Maybe by then I'll have sourced more shims..... I might even deal with the chattering clutch basket at the same time, as I now have the kit for that as well.

[jnnngs]

Hi,

Tell me what shims you need and I'll send you some - I have loads so pretty sure will have what you need (and in the UK)

Paul.