The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Dodger on 24.01. 2017 22:28

Title: Bent pushrod lesson
Post by: Dodger on 24.01. 2017 22:28
I thought I would share a recent experience that resulted in a bent pushrod. I had the head and barrels off my 61 GF over xmas to replace the cam followers and to decoke it.
I actually discovered worn cam followers, burnt valve guides and the valves were pretty pitted too. The real surprise was the top compression ring that fell into 2 pieces when I was inspecting it!
I duly replaced the the rings, cam followers, four new valves, springs and guides and reassembled it and set the valve clearances. All going well so I turned the motor over by hand which felt strangely very restricted and tight. So off with rocker box only to find a very bent pushrod.
After a lot detective work Morse would have been proud of, it turned out that the somebody in the past 50 years or so had fitted 1950s Road Rocket alloy head valves at some point complete with their respective caps and collets. I had taken care to fit the correct parts for the year but my mistake was to use the old spring caps and collets. This resulted in the springs when fitted to proper GF valves becoming coil bound and something had to give when the valve opened and in this case it was a pushrod. Moral of the story, never assume because the bike appeared to be running ok before it was dismantled that it has the correct parts fitted. I learnt the hard way I'm just relieved I didn't try to start it up.

It's all back together now by the way and running like a dream. (Complete with Gold Flash spring caps and collets!)
Title: Re: Bent pushrod lesson
Post by: RichardL on 25.01. 2017 06:21
Title: Re: Bent pushrod lesson
Post by: muskrat on 25.01. 2017 19:41
G'day Dodger,  *welcome*
Good of you to post your experience. A good lesson for anyone wishing to mix & match.
I recently had a similar problem. Fitted Super Rocket valves and hardware into my 54 A7SS head. I didn't need to install the head as I could see the springs would become bound at only 0.25" lift, the 357 cam gives about 0.35". I used the original A7SS springs and keepers (had to machine the taper) with the SR collets and valves.
Title: Re: Bent pushrod lesson
Post by: Dodger on 25.01. 2017 20:51
The one thing I did notice now I'm scooting about on the bike again, is that the engine has been breathing a bit more oil since the rebuild. I do vaguely recall reading somewhere that it's normal to see a bit of oil from the breather for a 1000 miles or so after a rebuild, particularly after fitting new rings. Does anyone know if their is any truth in this?
Title: Re: Bent pushrod lesson
Post by: Bsareg on 25.01. 2017 23:54
Did you deglaze the bore when fitting the rings? A dodge I've used in the past when rings wouldn't bed in is to drop some Vim into the plug hole and run the bike. Not good practice but it works and does no lasting damage provided the oil is changed as soon as the exhaust stops puffing oil
Title: Re: Bent pushrod lesson
Post by: Slippery Sam on 26.01. 2017 11:34
Thanks for sharing Dodger.  I'm just about to build up a head from bare so will take something from the lesson.
Reg - would you not have to be transported back to the 60s to get the Vim - LOL  not seen that in Tesco for a while!

Cheers Raymond.
Title: Re: Bent pushrod lesson
Post by: Dodger on 26.01. 2017 12:50
Ahh ...that would explain the reaction I got from the bloke in Halfords when I asked him if they stocked Vim;)( I am actually old enough to know what it is btw). 

1945 WD Matchless G3L/61 A10 Golden Flash/1978 T140E Bonneville.
Title: Re: Bent pushrod lesson
Post by: stu.andrews on 26.01. 2017 14:01
Vim, that's a bit drastic! Rings take a little while to bed in & any smoke to stop. By removing any bore glaze & running the engine in properly, making it work a little will soon bed the rings in. Don't be too gentle with it, just ride it normally without flogging it.
Title: Re: Bent pushrod lesson
Post by: muskrat on 26.01. 2017 19:26
Ah the old Bon Ami / Ajax trick. Used it to bed in rings & deglaze bore on the race bike after an overnight rebuild. Start it up hold it flat and throw 1/2 teaspoon into each carb. Run for a minute then change the oil. Ready for next race. *bright idea*
I certainly wouldn't advocate this for a road motor.
Title: Re: Bent pushrod lesson
Post by: Bsareg on 26.01. 2017 20:25
I've used Vim ( I agree very drastic ) when owners have used a quality oil when running in instead of a cheap oil . The additives in good oil seem to glaze the bores instead of allowing the rings to bed. Vim  saves a strip down to rebust (is that a word) the glaze
Title: Re: Bent pushrod lesson
Post by: chaterlea25 on 26.01. 2017 20:44
Hi Dodger
May I ask how/why you needed to open the engine to change the followers ?

I know there were  some dodgy followers about a while ago, but *ex*
The usual reason for follower wear is oil starvation due to a worn crank bush, this means that the pressure relief valve does not open allowing oil up to the cam trough  *eek*
Usually the cam is toast as well  *sad2*

Title: Re: Bent pushrod lesson
Post by: Dodger on 26.01. 2017 21:18
Hi John, to get access to the followers the barrels needed to come off so as is usually the case when taking engines to pieces while I was at it I fettled the cyl head. Discovering what I did fitted to the head it turned out to be one of my better decisions.

From what I was able see into the crankcase with the barrels lifted, the cam shaft looked ok to me and there was no shortage of oil in the trough. Two of the followers I took out certainly had indications of wear on them.

The clattering I had from the area of the followers has definitely gone now after replacing them. So apart from seeing a bit of oil breathing out of the motor it sounds and goes really well.

Thanks Bsareg for the Vim tip but somehow it doesn't seem the right way to treat an old motor. I think will just ride it and get some miles on the clock and keep an old rag handy to clean up after myself.
Title: Re: Bent pushrod lesson
Post by: Dodger on 28.01. 2017 15:35
Overbreathing oil problem resolved I changed the breather cork to a slighter thicker one and no more oil everywhere. Simples!