Starting a rebuild

[LIONELSMITH]

I have spent too long rebuilding my Golden Flash and am having problems starting. I am getting fuel though, I am getting a spark, it turns over with no issues. I have re-checked the ignition timing and all are OK. Yesterday I thought to check compression without disconnecting the carb on my cheap guage to check I had compression . The right cylinder showed around 50 ft/lbs but
the left cylinder did not register. I decided to strip down the head again. Having had a double re-bore from standard to 40 thou over, fitted +40 thou new pistons and rings set to 120 degree intervals around the pistons, I was confident of the pistons not leaking. As I had installed new guides and valves for the first time I wondered whether they were air tight. I tried a water test in the upended head with no leak at all.

With it dismantled still, has anybody got any idea what other test I can do or should I strip the head down to regrind the valves again just to see. I do not not have compressed air to do a leak test. I am at a loss to think what else could be causing the problem.
Thanks for any suggestions.

[Gup holland]

Was your valve clearance of the left cilinder in good order? Or sticky valve?

Gr alex

[cdsdorset]

Pour parafin down the ports. It will find any leaks.

[LIONELSMITH]

Thanks for the comments Gup Holland and cdsdorset. Valve clearances were double checked and are fine thanks. I had not thought of a sticking valve and this is the first time I have replaced guides AND valves. I will strip the head down again and check the valves move freely. Should I oil lightly?

[cdsdorset]

Are you sure the valve guides are correct. Did you fully recut the seats after fitting them?

[LIONELSMITH]

An interesting development. Since your helpful comments I took the head off and got my local engineer to check the valve guides and valve seats I had put in. One exhaust valve guide had gone in a little crooked, he re-seated this and he re-ground the valves again.
I have assumed the non-starting was, as it usually is, electrical, probably timing. This I checked today with a timing light (too long to go into) and it was spot on. I decided, therefore, it must be fuel. I took the carb off today to strip the lot but found the new paper air filter was brown and soiled, surprising since it has not started yet.
Daft question of the week, can the engine blow backwards. Could I have been pushing fuel into the filter rather than the engine? When I do the timing I check to see which cylinder at TDC has the valve closed to check the cycle, but why such a dirty new filter.
After the carb rebuild should I start it without a filter or put a new cleanable metal wire filter in its place. I just want Billy running.

[cdsdorset]

Just take the filter out and see what happens. Worry about it later.

[rhyatt]

Hmm.
Compression checks , always hold twistgrip wide open when kicking.
You may already ngk have tried the strength and colour of the spark, should be good blue crack.
You haven't got a suppressed plug cap in ht lead, throw it away ( this applies only if you have a magneto)

[LIONELSMITH]

Good news and not so good. at which point I turned off
After removing the air filter and rebuilding the carb the bike has started for the first time and was idling happily. BUT I am getting an intermittent loud metal on metal sound. It is not terminal as it ran until I turned off but is worrying. I think it has got to be tappets first to check. Has anyone had such a sound on first starting? I am getting no blue smoke from the exhaust so it may just need the oil to start lubricating. Any suggestions please.

[cdsdorset]

Did you check you wrre gettibg oil circulation before first starting it?

[LIONELSMITH]

Thanks cddorset. No I admit that I was to check on starting and I cant see any oil flow on running, probably not enough pressure running so briefly, certainly none kicking. It is a new SRM pump.
When I re-checked the tappets one push rod was not under the rocker but when I lifted the rocker it flipped back. 
I rebuilt the Rocker box with new Rocker shafts, replaced one of the rockers that had a crack and used new tougher push rods. I will dismantle again tomorrow check the cups, re-oil and rebuild. Can the rocker cups be deepened if worn?

[Pete Gill]

Good news and not so good. at which point I turned off
After removing the air filter and rebuilding the carb the bike has started for the first time and was idling happily. BUT I am getting an intermittent loud metal on metal sound. It is not terminal as it ran until I turned off but is worrying. I think it has got to be tappets first to check. Has anyone had such a sound on first starting? I am getting no blue smoke from the exhaust so it may just need the oil to start lubricating. Any suggestions please.

Is it possible a valve might be sticking open intermittently?
Perhaps hitting the piston when remaining open?
Pete

[rhyatt]

I would have hoped you could see oil returning to the tank.
Any oil squirted into the engine during assembly would have been returned to the tank .
So , was the oil pump primed with oil during assembly, no air in it.
Once started, the pump would return/scavenge assembly oil sitting in the sump, then a small pause of returning oil caused by fresh oil being circulated, then it would pick that up.

[neil1964]

Good news and not so good. at which point I turned off
After removing the air filter and rebuilding the carb the bike has started for the first time and was idling happily. BUT I am getting an intermittent loud metal on metal sound. It is not terminal as it ran until I turned off but is worrying. I think it has got to be tappets first to check. Has anyone had such a sound on first starting? I am getting no blue smoke from the exhaust so it may just need the oil to start lubricating. Any suggestions please.

Is it possible a valve might be sticking open intermittently?
Perhaps hitting the piston when remaining open?
Pete

Given your previous dodgy guide the noise made and latest findings of the pushrod that is the most likely thing.
I confess I had similar issue many many  years ago with a Tiger cub but it was because I fitted a medium CR piston but the head was previously tuned with o/s inlet valve.  Like you I realised not right, stripped it, did plasticine on piston test checked valve timing and polished the edge of the inlet valve cut out to get clearance cold and hot then all was good.
You may just find a sticky rocker shaft and the noise was the pushrod having acres of slack!

[LIONELSMITH]

Thanks for the replies Pete, Rhyatt and neil1964.
As said yesterday the rocker cover is now off and looks a little dry, although a drip or two of fresh oil had made it to the left rocker (maybe the pump worked after all?). My 67-267 rocker cup (right exhaust) is more worn than the others, probably the one I replaced, however, the 67-265 (right inlet) was causing the issue.
Neil sorry about the dodgy guide but how do you describe a noise, a single metallic clack? What confused me was that the engine still ticked over nicely. I was thinking rocker shaft which is why the Rocker box is off but thanks for the confirmation. I do like to think before acting.
I will force some oil though the oil holes in the rockers and rotate them to try to get the shafts lubricated.
Pete, my engineer thought the valves were OK so I am usually loathed to try and lubricate those as at running it will coke the combustion chamber when it gets through, but maybe a little on that valve. Some oil will drip down anyway.
Rhyatt, very good point about priming the pump, I didn't do it. I will have to have a look at the pump as I had the casing adapted to take a feed for the tacho but I was not convinced it was totally straight, just in case the oil pump shaft is damaged.

Further update.
After stripping the rocker box off and oiling I re-assembled. It starts first time runs 4-5 seconds there is a loud single clack sound and it stops. It restarts, same run time, same sound, same result. I tried this three times. I did put some oil down the suspect vale. Does this sound like a sticking valve?
I am going to have to take the rocker box and head off,measure the SRM push rods take the valves out and check for sticking valve. It does sound top end. I did also before the third restart unscrew the tacho cable and it did the same so it is not that.
To try and give an idea of the sound, it sounds like the clack you get hitting a metal table with a metal rod.
Any other ideas?