Tapping from engine - post CCT and value swap

[StuartWags]

Hello,


I am new to the forum but not new to VTRs, this is my 5th.

I brought a failed CCT bike a few months back. The previous owner try to fit a new, standard CCT but gave up when it did not spark back into life. I have had the head off and apart from 4 bent valves the head was useable. I replaced the valves from a spare rear head i had knocking about (usually just swap for another front head but budget was tight), set the clearences.

Rebuilt with the neaw standard CCT and sparked it up. It runs pretty good, carbs could do with a balance, clutch rumbles a bit but as expected. However, there is a load tapping noise at engine speed. Sounds like front end but really difficult to tell. Like a real bad valve clearance issue on one valve.

I have rechecked the valve timing, rechecked the valve clearences, even check for a bent cam but to no Joy. I have not checked the rear CCT yet.

I am starting to run out of time, money and ideas.

Next on the list
Swap both CCTs
Recheck valve timing and clearances

If this does not work then swap cam chains

if this does not work the swap head

if this does not work then give up and swap the engine or push off the nearest cliff

Now, i have read through the forum and realise this is not the first time. However, I am not sure I have seen the answer yet. I know people have had the same problem but has anyone ever solved it?

I have also eliminate all the other random stuff like drive chain, exhaust blowing etc., etc,

PLEASE HELP if possible - no cliffs in the fens

[tony.mon]

Firstly, check the rear CCT.

Then pop the cam covers off and compare the slack in the cam chain run between the sprockets. Should be some, max 10mm but I'd prefer to see 5-7mm.
You might need to take off the guide between the cams to see how much you have.
Don't run it like this but it'll be ok to turn over by hand.
Make sure you have the engine set at the correct places to check each cylinder's chain slack, same place as you set it to in order to change cct's.

But worse case could be a small end, maybe big end, depending on how much of a battering the piston took hitting those valves.
But TBH neither of those is very likely.

[StuartWags]

Tony,

Thanks for you input. I agree with your final comments, there was very light piston to valve contact. I have seen much hevier contact with do adverse effects on the small / bottom end. I will keep chipping away and feedback when i have found the issue

StuartWags

[lloydie]

Did you lap the valves in ?


Can't ride but it don't stop me trying

[StuartWags]

lloydiecbr,

I did lap the valves in and they all seemed to move freely. However, you have just reminded me, one of the valves did have a couple of dents (in cylinder side). Like it had struck something in the cylinder, with the valve in the closed position.

Bent or sticking valve is still on my list. I will be so pi55ed off with myself if i installed a dodgy valve.

I will check out the other stuff (CCTs and cam chain) before a rip the head off

thanks


StuartWags

[StuartWags]

Swapped the front CCT for a known good one
Rear clearance checked (again)
rear CCT removed and checked out OK
no impact on tapping
I did take the kill or cure approach at this point and took it for a run. The performance is spot on everywhere, pops the front up under hard acceleration, goes like stink up to 130 mph. No farting and banging anywhere. In fact, it is one of the best performing VTRs i have had. I am thinking this is probably not a sticking valve.

However, the tapping is relentless. Consistantly there and does not change under acceleration and decceleration (i would have though cam chain slap would, but guessing)

I will recheck the front valve clearances and cam chain slack tomorrow.

Next on the list
cam chain swap followed by a head swap if no joy

[tony.mon]

lloydiecbr,

, one of the valves did have a couple of dents (in cylinder side). Like it had struck something in the cylinder, with the valve in the closed position.


StuartWags

I really can't see how something powerful enough to leave a dent in a hard steel valve would have only done it in the closed position; it must have happened when the valve was connecting with something, usually the piston.

So swap that valve out.
did you use 2nd hand valves, then?

Because it sounds as though that one valve is not seating correctly; so under load/stresses/heat the clearance is wrong.

do it before the valve head snaps off!

When you seat/lap the valves in, could you check that there was an even grey line in the lapping paste, when you lifted the valve out with the lapping stick?
It should be even all the way round (don't rotate the valve when lifting it out, just straight out of the guide).
Also no more than 3mm wide, preferably nearer 2mm.
You can get the valve seats re-cut, any tuner will be able to do this, but if they're too deeply pocketed it will ruin performance.

[StuartWags]

Tony,

That was my assumption too... , I assumed poor manufacture as there was no other damage to the head and valves. And yes they where 2nd hand valves but there is no other damage to the donor head.

The valve seats did not look pocketed on the bike head and a nice 2mm strip of grey was achieved with minor effort. I did not do a pull out test thought.

The thing that is doing my head in at the moment, is that the perfromance is excellent.

I am preparing myself for a head swap, but need to be totally sure that all the easyer stuff is rulled out first.

I am convinced it is a valve clearance issue, or timing chain tension related issue or possibly a broken valve spring... but these are just random ideas that i have not rulled out yet

Stuart Wags

[turbo_billy]

Probably a long shot but did you use genuine Honda gaskets on the heads and barrels? I had something very similar a few years ago with a CB900F I bought as a project. Metallic ticking noise when the engine was running but pulled fine. Had the head of 2 or 3 times, checked valves, chains, everything....found nothing and still ticked. Eventually gave up and bought another running motor and sold the other for spares. When the guy stripped it he found the gaskets were much thinner than the originals and that was enough for the pistons to go that little bit further up the bores and just kiss the other moving parts.
Unlikely in your case but just another idea in the mix.
Regards
Tim

[StuartWags]

Turbo,

Gasket supplied by David Silver so I do not expect an issue but will check if i have to remove the head.

I remember being suppied head gasket for a 1300 car and the gasket turned out to be one for and 1100. That REALLY caused some interesting problems

Cheers,