The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Mosin on 10.02. 2019 16:44

Title: Pushrod puzzle
Post by: Mosin on 10.02. 2019 16:44
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?
Title: Re: Pushrod puzzle
Post by: Servodyne on 10.02. 2019 16:53
It sounds like the inlet valves could be sticking open for some reason. Is it an iron head with bronze valve guides?
Title: Re: Pushrod puzzle
Post by: RichardL on 10.02. 2019 16:55
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.



Title: Re: Pushrod puzzle
Post by: Mosin on 10.02. 2019 18:24
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.
Title: Re: Pushrod puzzle
Post by: Greybeard on 10.02. 2019 19:05
I know it's a daft thing to ask, but are you sure you have the cams in the correct position for adjustment?
Title: Re: Pushrod puzzle
Post by: bsa-bill on 10.02. 2019 19:19
Quote
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



Title: Re: Pushrod puzzle
Post by: KiwiGF on 10.02. 2019 19:25
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.
Title: Re: Pushrod puzzle
Post by: muskrat on 10.02. 2019 19:27
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.
Title: Re: Pushrod puzzle
Post by: Mosin on 10.02. 2019 20:02
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!
Title: Re: Pushrod puzzle
Post by: Peter in Aus on 11.02. 2019 01:06
I think Servodyne is right, valves sticking a bit since you have fitted new valve guides.
Peter
Title: Re: Pushrod puzzle
Post by: Mosin on 11.02. 2019 08:17
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"?
Title: Re: Pushrod puzzle
Post by: kiwipom on 11.02. 2019 08:43
hi guys, Mosin i think it is off with the head and out with the reamer, cheers
Title: Re: Pushrod puzzle
Post by: Mosin on 11.02. 2019 09:49
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.  *sad2*
Title: Re: Pushrod puzzle
Post by: beezermacc on 11.02. 2019 10:14
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.
Title: Re: Pushrod puzzle
Post by: Swarfcut on 11.02. 2019 10:24
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.
Title: Re: Pushrod puzzle
Post by: Mosin on 11.02. 2019 19:50
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.
Title: Re: Pushrod puzzle
Post by: Swarfcut on 11.02. 2019 22:31
    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.
Title: Re: Pushrod puzzle
Post by: Peter in Aus on 12.02. 2019 00:11
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 
Title: Re: Pushrod puzzle
Post by: Mosin on 12.02. 2019 09:38
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.
Title: Re: Pushrod puzzle
Post by: Greybeard on 12.02. 2019 09:40
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.
Title: Re: Pushrod puzzle
Post by: duTch on 12.02. 2019 10:02

 
Quote
..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  *conf2* , but took steps to ensure it didn't happen,  but can easily see how it can happen without due care

Title: Re: Pushrod puzzle
Post by: bikerbob on 12.02. 2019 10:11
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.
Title: Re: Pushrod puzzle
Post by: Mosin on 12.02. 2019 11:20
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.
Title: Re: Pushrod puzzle
Post by: Swarfcut on 12.02. 2019 11:30
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.
Title: Re: Pushrod puzzle
Post by: Mosin on 12.02. 2019 11:51
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.
Title: Re: Pushrod puzzle
Post by: Mosin on 13.02. 2019 21:07
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!
Title: Re: Pushrod puzzle
Post by: Swarfcut on 13.02. 2019 21:33
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.
Title: Re: Pushrod puzzle
Post by: Servodyne on 13.02. 2019 22:09
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.
Title: Re: Pushrod puzzle
Post by: RichardL on 14.02. 2019 06:17

 
Quote
..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. *smile*

Richard L.

Title: Re: Pushrod puzzle
Post by: Mosin on 14.02. 2019 14:35
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
Title: Re: Pushrod puzzle
Post by: chaterlea25 on 14.02. 2019 14:49
Hi Mosin
The shop that did the work are probably more used to modern engines that require ultra close tolerances
OR
They never bothered reaming / honing the guides at all once the valve went into the guide  *sad2* *eek*

John
Title: Re: Pushrod puzzle
Post by: Bsalloyd on 14.02. 2019 20:22
The only thing I have not heard is that sometimes the valve spring retainers will foul the inside of the rocker box. It does not happen often, check for crescent shaped marks on the inner area of the rocker box. Lloyd L.
Title: Re: Pushrod puzzle
Post by: muskrat on 15.02. 2019 20:17
G'day Mosin.
Good to hear your getting to the bottom of it.
LLoyd has a point. If an iron head or SS rockerbox is fitted to a SR this will happen. The SR rockerbox is relieved in that area to give clearance.
Cheers
Title: Re: Pushrod puzzle
Post by: Scott and Jay on 07.03. 2019 01:45
Hi Mosin,

I don't leaving a newly-rebuild engine idling is good. I have heard of them seizing up after this. I believe in the early bedding in of the rings (having put them in dry, with just a bit of light oil on the skirt). I used the "Klaus" method - of "stationery" running in. After that, no:-
- excessive idling
- high revs
- lugging in too low a gear
for the first 500 miles...
Title: Re: Pushrod puzzle
Post by: bikerboy on 21.03. 2019 00:38
I would still be a bit suspicious like muskrat I have had a10 rocker boxes on and off a million times and can do them in my sleep but I have never been able to get a pushrod back in without raising the box just a mm or 2. I suppose you could force the valve open to do this but if you are not doing that then I really would wonder how those pushrods can come in and out like that