GB is not OK!

[KiwiGF]

I've been studying the BSA parts list. Here is a possible explanation of the problem. Pushrod lengths: The Plunger A10 uses part No's 67-360 and 67-362. The Star Twin and Shooting Star uses part No's 67-979 & 67-977. I've fitted a camshaft intended for the Star Twin & Shooting Star. The cam I have now has higher lift, so maybe the pushrods I have are too long. Anyone?

It’s a while back but when I compared the 334 cam and the new 356 cam (from srm) I was surprised how little extra lift there was, from memory less than 020” so I doubt this is your cause of your problem?

As an aside I actually “complained” to srm who explained they had run out of 356 cams and the “emergency” batch they made was based on a blank not 100% correct, which resulted in the slightly lower lift to std, it was only a few thou so they thought I would not notice I guess. They offered to replace it but as I had already waited months for them to make a batch of cams, I kept it.

Edit: I know the problem goes away when tappets are slackened but thought I’d mention the classic error of the front primary chaincase bolts hitting the crank......just in case you moved these?

Edit: The lift I meant was cam, e.g the difference between cam base circle and cam lobe measurements. The valve lift is greater, as the rocker has “arms” of unequal length.

[Black Sheep]

The 500 pushrods are of course shorter than the 650 ones. The difference in lift of the 356 cam is miniscule - I really can't see it causing the valves to hit the pistons. There has to be another explanation. Coil bound valve springs are a possibility. A good night's sleep and a few more cups of tea will help. Don't rush it.

[muskrat]

G'day GB
I agree with morris in that cam followers & push rods won't make any difference. Roy and John have a point on coil bound valve springs. I put a 357 in the A7 plunger without any problems with springs (just the cam rubbing the case in the trough). Std A10 valve lift 0.265", 356 = 0.301", 357 = 0.338". General rule is that at full lift you should be able to compress the spring another 0.060" till it's coil bound.
Cheers

[duTch]

 

......Edit: I know the problem goes away when tappets are slackened but thought I’d mention the classic error of the front primary chaincase bolts hitting the crank......just in case you moved these?   

 Good idea but Plungers don't have those (two very short studs carry the chain tensioner where the S/a rear bolts go )

 GB- does it jam up both sides on each respective cycle or just one ?
  just a quick look at the cam timing suggests that no valve is *fully* open at TDC....also for what it's worth, I think I recall discussion with B-Bill when I was doing mine, about the rocker arms being longer on the adjuster side than the 'cup' side- maybe worth considering when calculating travels (?)

 

General rule is that at full lift you should be able to compress the spring another 0.060" till it's coil bound........

  So I guess you'll be measuring the pushrod lengths now?? 

 I've a couple of hours solid looking 'wet-stuff from the sky' heading my way very soon, so won't be doing much today....not that's much help to you....

 *edit; Yes I have a 357 cam in my Plunger, but also have an Alloy head with S/R springs, and I dunno if those springs would fit in a iron head, but others will know 

 

[muskrat]

At top dead center on the exhaust stroke both valves are partially open and you should be able to push the valve down a further 0.06" as well.
Cheers

[Greybeard]

Thanks guys. I went back to the shed. I am still getting the same problem! I made sure the push-rods were in their cam followers before I put the rocker box on. I got fed up and had a drink and a bath. As BlackSheep says, a good night's sleep may get it sorted tomorrow. I'll be checking for coil binding in the valve springs.

[muskrat]

I've always found the top cups are mostly the problem and the inlets more than the exhaust even though the ex are harder to see.
Cheers

[duTch]

 

At top dead center on the exhaust stroke both valves are partially open and you should be able to push the valve down a further 0.06" as well.

 Kinda what I had in mind.... ...

 

I've always found the top cups are mostly the problem and the inlets more than the exhaust even though the ex are harder to see.

 I found the 'hard to see' ones can be just visible over the top of the shaft/s ( maybe with a bright pinpoint light and small mirror if necessary) a bit of a jiggle shows if the rods are in ok....

[Greybeard]

I have a new small super bright torch; using that it's possible to see that the rods are in the rocker cups. Not so easy to see the bottom of the pushrods.

[Greybeard]

It looks like the problem is binding of the valve springs: with an inlet rocker fully down I cannot get a 3 Thou feeler between the coils! What to do about this; that's the next question.

[RoyC]

It looks like the problem is binding of the valve springs: with an inlet rocker fully down I cannot get a 3 Thou feeler between the coils! What to do about this; that's the next question.

  a. Change the cam.

 b. Machine the cylinder head spring seat
 deeper (.050” to .075” max) with the
 appropriate Crower spring seat cutter

https://www.crower.com/media/pdf/valvespring.pdf

[Greybeard]

If I set the tappets to 30 thou the engine turns ok.  I'm thinking about doubling up the solid copper head gasket, just to get me going for the weekend. The copper gasket should add about 30 thou to the clearance. Thoughts?

[RoyC]

If I set the tappets to 30 thou the engine turns ok.  I'm thinking about doubling up the solid copper head gasket, just to get me going for the weekend. The copper gasket should add about 30 thou to the clearance. Thoughts?

But won't you still have the same problem when the tappets are set to the correct size ?

[Greybeard]

Thanks for coming back with that Roy; of course you are right. BUGGER! Now I'm considering taking metal off the springs!

[RoyC]

Thanks for coming back with that Roy; of course you are right. BUGGER! Now I'm considering taking metal off the springs!

Looks as though you are looking for .060" from somewhere.