The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Greybeard on 30.06. 2018 15:56

Title: Now harder to kick start
Post by: Greybeard on 30.06. 2018 15:56
As you may recall, I recently did some work on my A10 semi-unit Plunger engine. The camshaft was changed from standard to the Road Rocket 357? cam. I still have flat topped low comp pistons. Apart from the camshaft and followers, the engine has new little end bushes, new piston rings, new big end shells. The ignition timing was set as per Road Rocket, 9/32"? BTDC. Since the rebuild the engine now requires a fairly heavy kick to start it. After the previous rebuild, six years ago the engine was pretty easy to kick over to start. If I didn't know better, I'd say the engine had higher compression pistons. It's strange! Is this phenomenon caused by the new camshaft, or the more advanced ignition timing? I don't believe the engine is still stiff; I've done a few hundred miles since the rebuild.
Title: Re: Now harder to kick start
Post by: JulianS on 30.06. 2018 16:44
Timing could be out - Road and Super Rocket given as 3/8 BTDC until 1960 when it changed to 13/32.
Title: Re: Now harder to kick start
Post by: Triton Thrasher on 30.06. 2018 17:06
Sounds like your new rings have bedded in properly.
Title: Re: Now harder to kick start
Post by: Greybeard on 30.06. 2018 17:45
Sounds like your new rings have bedded in properly.
Yes, but six years ago I put new rings on these pistons and the bike started easier, as you can see in this video, taken soon after the rebuild: https://youtu.be/GL0wT8kriTA
Title: Re: Now harder to kick start
Post by: Triton Thrasher on 30.06. 2018 20:26
Maybe six years ago the rings did not bed in so well and the engine had poor compression.
Title: Re: Now harder to kick start
Post by: muskrat on 30.06. 2018 21:52
G'day GB.
The 357 will only make a tiny difference to the kickstart pressure. My A7 plunger with a 357 and 7.5:1 pistons is a no effort starter. TT may be right.
Cheers
Title: Re: Now harder to kick start
Post by: stanwhite on 30.06. 2018 22:56
New rods?  A bit longer?  (apparently, there are some out there).  Slightly higher compression as a result?

Thinner head gasket, or you forgot to fit it?  *smile*

Or...  This time, you lapped the valves in properly *sarcastic*

Cheers,

 Stan.
Title: Re: Now harder to kick start
Post by: berger on 30.06. 2018 23:02
I have not been to the pub, I think your leg needs some of popeyes spinache ;)
Title: Re: Now harder to kick start
Post by: chaterlea25 on 30.06. 2018 23:16
Hi GB,
Quote
The camshaft was changed from standard to the Road Rocket 357? cam.

I'm pretty sure I remember the new cam is a 356  *????*

Anyway that should not make a difference to starting
As the so called petrol available now is crap retarding the ignition a tad  helps
As the pistons are low comp there's no point in setting to the RR or SR  figures (that are not applicable to today's fuel anyway)
I seem to remember Orabanda's best dyno figures were with using 32 degrees BTDC  *????*

John
Title: Re: Now harder to kick start
Post by: worntorn on 01.07. 2018 06:20
A hot cam with more overlap should reduce kickover compression a little.
This is partially offset by the extra force needed to compress the valve springs more, if lift is greater.
All in all it should still be a bit easier to kick thru than with lower performance, lesser overlap style of cam.
Title: Re: Now harder to kick start
Post by: Greybeard on 01.07. 2018 08:21
Thanks for all those comments chaps. I reckon the timing may have moved a bit and it is now a bit too advanced. As I'm not home I may have to close the points a bit to retard timing. I have that right, don't I?
Title: Re: Now harder to kick start
Post by: Triton Thrasher on 01.07. 2018 08:36
If it’s not kicking back, I don’t see how ignition timing can make the engine harder to turn over.
Title: Re: Now harder to kick start
Post by: Greybeard on 01.07. 2018 08:47
If it’s not kicking back, I don’t see how ignition timing can make the engine harder to turn over.
She was fighting me yesterday with some kickbacks. Mind you, I'm not used to putting a lot of force into the kick so I was being less than persuasive about it! I'll see how things go this morning.
Title: Re: Now harder to kick start
Post by: duTch on 01.07. 2018 09:41

 With my 357 & flat-tops, as long as I'm assertive, I don't generally have trouble, except when I get complacent as I did one day leaving the Bottl-oh with a box on the tank.... *eek*
Title: Re: Now harder to kick start
Post by: bsa-bill on 01.07. 2018 10:44
Got it - GB bet you keep your wallet in your right hand trouser pocket, recent events have lightened it considerably therefore requiring more effort on your part to get that KS lever down - do you have an odd R/H clog lying around  *smile*
Title: Re: Now harder to kick start
Post by: KiwiGF on 01.07. 2018 11:05
If it’s not kicking back, I don’t see how ignition timing can make the engine harder to turn over.

I agree, and mine almost NEVER kicks back, and has auto advance (via BTH mag tho), and flat tops.

An A10 with the original domed inwards pistons (6.5:1?) I once kicked was SO easy to kick over compared to my bike I thought it must be low on comp but apparently it was on original bore and didn’t burn oil. It almost felt like it had no compression at all.
Title: Re: Now harder to kick start
Post by: mugwump on 01.07. 2018 11:32
Its much easier kicking a bike over if the kickstarter is set a bit lower, say about 10 o,clock. Saves the knee joint strain too.
Title: Re: Now harder to kick start
Post by: morris on 01.07. 2018 14:55
Sounds like your new rings have bedded in properly.
Yes, but six years ago I put new rings on these pistons and the bike started easier, as you can see in this video, taken soon after the rebuild: https://youtu.be/GL0wT8kriTA
Six years ago you where six years younger GB!

I do find that since the SA had a rebore with new pistons (flat tops, same as the ones that came out) and new rings there is noticeably more compression than before
Title: Re: Now harder to kick start
Post by: Greybeard on 01.07. 2018 19:15
Six years ago you where six years younger GB!
*smile*
Quote
I do find that since the SA had a rebore with new pistons (flat tops, same as the ones that came out) and new rings there is noticeably more compression than before
I'd better learn to kick-start then!
Title: Re: Now harder to kick start
Post by: Greybeard on 01.07. 2018 19:18
Its much easier kicking a bike over if the kickstarter is set a bit lower, say about 10 o,clock. Saves the knee joint strain too.
Yes, I've been using the clutch to get get the kick starter half way down before I give it the boot.
Title: Re: Now harder to kick start
Post by: Greybeard on 28.07. 2018 20:38
Today I retimed the engine to 11/32" BTDC, as per the book I have not ridden it since then.