Pushrod puzzle

[Mosin]

My newly rebuilt engine is now fitted and after a few minor teething problems I got her fired up for the first time yesterday. She ran nicely at tick over, but I didn't try to ride her anywhere.

This morning I started her up absolutely fine and left her ticking over. After a couple of minutes the engine died and wouldn't start. I was getting a nice healthy spark from my Pazon and lots of alarming backfires through the bellhousing, but she just would not start. I had tightened up the rocker box bolts this morning and wondered if this had knocked the valve clearances out, so I removed the inspection cover and was amazed to discover that both the inlet pushrods had jumped out of their cups. I managed to get them realigned without having to remove the rockerbox and re-set all four clearances. She started up first kick and ticked over nicely for a few minutes before stopping. Once again I got nothing except backfiring and flames from the carb.

This time when I removed the tappet inspection cover I discovered that the clearances were at zero and were tight. (Only on the inlet side. The exhaust ones were fine). So I once again re-set the gaps, double checked them and started the bike. And once again she ran perfectly for a minute or two before cutting out and refusing to start. This time when I checked the pushrods, I discovered that once again the two inlet ones had jumped out of their cups in the rockerbox.

At this point I gave up for the day and came home for my dinner. Please can anyone suggest what I am doing wrong here?

[Servodyne]

It sounds like the inlet valves could be sticking open for some reason. Is it an iron head with bronze valve guides?

[RichardL]

I believe what might be happening here is landing the bottom ends of the pushrods on the lips of the lifters, rather than in the lifter cups. Show's up as adjusters unusually extended from the rocker arms. DAMHIK.

Richard L.

[Mosin]

It sounds like the inlet valves could be sticking open for some reason. Is it an iron head with bronze valve guides?

No, it is an alloy head. I should have said that it has just had new valves/guides/springs/camshaft/followers and pushrods fitted.

[Greybeard]

I know it's a daft thing to ask, but are you sure you have the cams in the correct position for adjustment?

[bsa-bill]

but are you sure you have the cams in the correct position for adjustment?

Yep thats the first thing I thought but wanted to wait to see if it came up, yes make sure one cylinder valves are rocking when measuring the other other

[KiwiGF]

As per other post I’d  double check you are setting the clearance with the cam in the right position eg with follower on the base circle, it’s easy to get this wrong especially with 5he higher duration cams.

Has it got new alloy pushrods? I ask as there were some in the market place that had incorrectly radiussed ends, causing excessive wear and sticking in the rockers, making setting clearances tricky.

[muskrat]

G'day Mosin.
All three suggestions have merit. I'm leaning towards Servodyne's sticky valves. OK when cold but stick as the valves get hotter and grow faster than the guide/head.
Unusual (for me anyway) to be able to put the pushrods back in the cups without lifting the box a mm or three.
Cheers
ps: Bill got in first. I do tappets with the opposite valve fully down. Left inlet fully open (down) do the right inlet.

[Mosin]

I made absolutely sure that when doing the left inlet valve clearance I had the right hand one pushed right down (open), and vice-versa when doing the other cylinder, so at least that rules out that possibility.

I suppose I should just be grateful that I am blessed with long thin fingers so I don't have to keep lifting the box off and upsetting the exhaust side too!

[Peter in Aus]

I think Servodyne is right, valves sticking a bit since you have fitted new valve guides.
Peter

[Mosin]

Ok, so it is starting to sound like the inlet valves are sticking. Thanks for all the suggestions folks. But the question now is "what can I do about it"?

[kiwipom]

hi guys, Mosin i think it is off with the head and out with the reamer, cheers

[Mosin]

hi guys, Mosin i think it is off with the head and out with the reamer, cheers

I had a horrible feeling that was going to be the answer. 

[beezermacc]

It seems odd that both inlet valves are sticking at the same time. I would expect one to stick before the other and the bike to go on one cylinder before it stops altogether. I have only had a sticky valve problem on one occasion when the cause turned out to be over-retarded ignition causing the cylinder head to get too hot. Another thing worth checking is oil flow to the inlet rocker shaft. I suggest slackening the banjo when you start the bike just to check plenty of oil is coming out.

[Swarfcut]

Mosin... Before you rip it apart, check your clearances again (back of the cam, valve closed) and run it gently with the valve covers off. Observe the rocker movements and squirt oil onto the valve stems, through the valve spring  coils, as it ticks over. Maybe it just needs a few minutes of well lubricated running to get the valves closing as they should. You can also check oil feed to the valve gear at the same time. If it is a case of head off, check for bowed pushrods, and also their fit into rocker and follower cups. They should not bind, but still be a snug fit. Most unusual for a pushrod to jump out if all assembled and set up correctly. If the motor is A10, any chance they are A7 exhaust pushrods, masquerading  as A10 inlets? Dimensions are somewhere out there, so you can see if you have the right pushrods. Clutching at straws here on your behalf, worst case is a bit of work and a new head gasket. Plus the ever popular re- seat the pushrods  game.

 Good luck, Swarfy.