Pushrod puzzle

[Mosin]

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.

Thanks for the suggestions. I must admit it has me flummoxed. I will give it another go tomorrow. I want to try every other possibility before having to remove the head again. It has had a brand new set of push rods, and I checked they were straight before they went in, so that rules out the possibility of them being bowed.

[Swarfcut]

    Those pushrods may have been OK when installed, but a situation where the engine has run with them rattling loose as described is the way in which most bends and bows occur. Good idea to check the lengths anyway against published data. Spitting back down the inlet tract would indicate inlet valves not sealing, either by mechanical binding in the guides and rockers, weak/ broken springs or maladjustment of the valve gear. Assuming the valve seats are OK, and the valves are the right ones for the head, plus the timing gears and ignition timing are set up correctly.

 Swarfy.

[Peter in Aus]

If it was me I would be taking the head off before trying to start it again, best to find out what is wrong before doing more damage to the motor.
The A7 long stroke I did up some years back suffered from the valve guides being to tight, it would spit back through the carby and carry on like a pork chop when hot, eased the guides out that fixed the problem, but the push rods did not jump out, so your's could be something else.
Hope you can sort it without much trouble.
Peter 

[Mosin]

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.

Has anyone else ever experienced this? I am sitting at my desk this morning playing around with an old push rod and cam follower and I can see how it could happen.

[Greybeard]

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.

Has anyone else ever experienced this? I am sitting at my desk this morning playing around with an old push rod and cam follower and I can see how it could happen.

Yes.

[duTch]

 

..Quote from: RichardL on February 11, 2019, 02:55:13

    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.


Has anyone else ever experienced this? I am sitting at my desk this morning playing around with an old push rod and cam follower and I can see how it could happen..

 No  , but took steps to ensure it didn't happen,  but can easily see how it can happen without due care

[bikerbob]

I think you need to do some checking on those push rods as Musky say's I also cannot get the push rods in place without lifting the rocker box up this is on both A10 and A7.

[Mosin]

Ok, It sounds like I am just going to have to bite the bullet and take the rocker cover off. Can anyone point me in the direction of the correct pushrod lengths? I have run a search, but can't  find them.

[Swarfcut]

Yes... Mine started up fine but ran rough on anything but light throttle. Any quicker, spat back and miss fired. Sent me down the ignition and carb route. A mechanical fault was then the only option......found witness marks where the pushrods had rubbed together, plus a nice bend in each.

   Once the rockerbox is roughly in place, but not fully tightened down, I set the follower on the back of the cam, slacken the tappet adjuster right off and steady the pushrod in a shepherd's crook of bent wire. Feel the top of the pushrod and raise the adjuster end of the rocker to make sure the rod fully enters the cup. Still with downward pressure, rattle the pushrod to make sure it is seated in the follower cup.

 Being a Gynaecologist or a Rock Guitar Axeman is an advantage, plus good eyes and a torch.   Or a Huntmaster Rocker Box.

 From my archives A7 Inlet   8 1/16"         Exhaust 9"

                          A10 Inlet   8 1/2"           Exhaust 9 1/2"

   From way back so in good old inches.    Nominal lengths, as published back in the day.

 Swarfy.

[Mosin]

Yes... Mine started up fine but ran rough on anything but light throttle. Any quicker, spat back and miss fired. Sent me down the ignition and carb route. A mechanical fault was then the only option......found witness marks where the pushrods had rubbed together, plus a nice bend in each.

   Once the rockerbox is roughly in place, but not fully tightened down, I set the follower on the back of the cam, slacken the tappet adjuster right off and steady the pushrod in a shepherd's crook of bent wire. Feel the top of the pushrod and raise the adjuster end of the rocker to make sure the rod fully enters the cup. Still with downward pressure, rattle the pushrod to make sure it is seated in the follower cup.

 Being a Gynaecologist or a Rock Guitar Axeman is an advantage, plus good eyes and a torch.   Or a Huntmaster Rocker Box.

 From my archives A7 Inlet   8 1/16"         Exhaust 9"

                          A10 Inlet   8 1/2"           Exhaust 9 1/2"

   From way back so in good old inches.    Nominal lengths, as published back in the day.

 Swarfy.

Now that is interesting. I would have thought that the only way the rods could jump out would be if I had accidentally placed a shorter rod in somewhere that required a longer one? BUT... I am having problems with the inlet side of my A7 (the shortest of all) so therefore this cannot be the case? Or am I completely barking up the wrong tree?

Incidentally, I am an enthusiastic competitive lock-picker, so working in tight spaces with minute tolerances and zero visibility is something which I am very familiar with. This probably helps! I found that a narrow piece of dowel with a V cut in the end can be introduced through the exhaust side and used to lift the pushrod into position. I was then able to drop the cup down onto the end of the rod using the method outlined above.

[Mosin]

This afternoon I bit the bullet and removed the rocker box.All four pushrods were the right length, all in the right places, and all nice and straight. Just out of interest I gave one of the inlet valves a tap with a hammer and it jumped closed. Aaaaah! Next job was to remove the head and I discovered that both the inlet valves were so tight that they could not be moved by hand. I am just glad that I didn't try and start it! So I guess that solves that problem. Now the head is away back to the engineering shop to have the guides reamed out slightly and then I will put the whole lot back together and try again!

[Swarfcut]

What a lucky man you are. No damage, the fault found and an easy remedy.  Makes you wonder why your engine folks got it slightly wrong.  If it comes back in bits, for you to assemble, check the valve stems are not bent. A quick spin in a cordless drill will show any wobble. I always assemble the valves with a dab of grease down the guide for lubrication on initial dry start up.

 Swarfy.

[Servodyne]

If it comes back in bits, for you to assemble, check the valve stems are not bent.
 Swarfy.

Good point as there is a good chance that the pistons may have given the valve heads a smack when they stuck open. It'll soon be noticeable when it comes to lapping the valves in.

[RichardL]

 

..Quote from: RichardL on February 11, 2019, 02:55:13

    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.


Has anyone else ever experienced this? I am sitting at my desk this morning playing around with an old push rod and cam follower and I can see how it could happen..

...  but can easily see how it can happen without due care

If I started an old-man rock band, "Without Due Care" would be a great name.

Richard L.

[Mosin]

When I Removed the head I checked the top of both pistons and there was no sign at all that they had been struck by the valves, and the pistons are both brand new, so any scratches or dints would have shown up.

When I first assembled the head I put a dab of grease on the valve stems as suggested, and I think that it was probably this which allowed the bike to run in the first place. It was once this grease had worn away that the valves nipped up.

Strange that it was the inlet valves which nipped up. If anything I would have expected it to be the exhaust ones as they are more exposed to heat.

Oh well, you live and learn!

Mosin