BritBike Forum logo
BritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorBritBike Sponsor SteadfastCyclesBritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorHepolite PistonsBritBike Sponsor
Upgrade to: Premium Membership | Gold Membership | Life Membership | Vendor Membership | Site Sponsor Membership
Member Spotlight
Magnetoman
Magnetoman
U.S.
Posts: 6,394
Joined: November 2011
New BritBike book out!
ShoutChat
Comment Guidelines: Do post respectful and insightful comments. Don't flame, hate, spam.
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Previous Thread
Next Thread
Print Thread
Rate Thread
Joined: Feb 2018
Posts: 179
Likes: 7
T
Britbike forum member
OP Offline
Britbike forum member
T
Joined: Feb 2018
Posts: 179
Likes: 7
Ride #3 ended in more top end damage. frown

I took it out for about 10 miles and planned on tuning the carburetor. Again, toward the end of the ride when the engine was warm I noticed more top end noise. Then when adjusting the carb, things went wonky again and I shut it down. This afternoon I took the valve cover off to find two more bent intake pushrods and another broken L Intake Rocker.

I called the mechanic who rebuilt the head. He thinks the problem is coil binding. He had the cam when he set up the valve springs. He said it is not the stock BSA cam, but one of the sport cams. He said at maximum lift there should be about a 0.030 gap between the spring coils. I couldn't fit a 0.030 feeler between any of the intake or exhaust spring coils at maximum lift. Sooooo.

The plan is to order new push rods and rocker. Assemble the top end, and DO NOT attempt to start. He wants me to bring the bike to him so that he can check the springs at maximum lift to determine the best correction. He mentioned removing shims on the valve springs, deepening the spring pockets in the head to allow for proper spring pressure, or shortening the push rods.

I'm pretty bummed. I feel like this is one of those things an experienced mechanic would have checked and avoided breaking things.
The first time this happened I thought it was builder error. I thought I had set the push rod on the edge of the cam follower instead of seating it on the follower.
This time I was careful to make sure the pushrod was properly seating on the cam follower. But I didn't know to check valve travel for for coil binding. It made perfect sense when he explained it.
If I ever rebuild an engine again, I will know to check such things.

Sigh.... dang so close.

Support Your #1 BritBike Forum!

Check out British motorcycles for sale: British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Joined: Feb 2018
Posts: 179
Likes: 7
T
Britbike forum member
OP Offline
Britbike forum member
T
Joined: Feb 2018
Posts: 179
Likes: 7
Is there a back story on A65 cams? The parts manual I have list one cam for the Lightning, Thunderbolt, and Firebird, 68-473. The A50 Royal Star has a different cam number, 68-103.
But..... In the BSA Workshop manual, in the General Data Section for the Lightening on page GD4 the Valve Timing points are listed for the Sports Camshaft. Further back on GD 15, in the section for the A50 Royal Star, a standard camshaft is mentioned.
If the parts book shows one cam for A50 and one cam for A65, why the distinction between Standard A50 cam and Sports A65 Cam.
For the A65, were different cams available? Standard, Sport, Racing? Or was there really only one cam. I remember, and may have pictures of my cam clearly stamped with 68-473.

Thanks

Tracey

Joined: Aug 2001
Posts: 5,489
Likes: 75
Britbike forum member
Online Content
Britbike forum member
Joined: Aug 2001
Posts: 5,489
Likes: 75
I think you have bad pattern valve springs, there are two cams for A65s early and late , later post 68 have the spitfire cam, its not mega radical, pretty tame compared to DBD Goldstar cams, if you have fitted a cam with more lift or have used bad pattern springs then you will get coil bind.
What springs did you use.? Coil binding can also be from fitting oversized inlet valves which sit too far into the combustion chamber causing the valves to be short on valve spring height.

This should be picked up on assembly, as the valve reaches full lift the motor will be "tight " as it reaches full valve lift, a sense of mechanical sympathy will pick this out.
Do not buy valve springs off e bay. If you fit oversize inlet valve , take careful measurements,


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Joined: Jan 2014
Posts: 1,030
Likes: 56
N
Britbike forum member
Offline
Britbike forum member
N
Joined: Jan 2014
Posts: 1,030
Likes: 56
It appears there are a load of crap pattern valve springs about at the moment.
Make sure you can get a 50 feeler in the coils at full lift to be safe. It's a pretty
good guide.
You don't want to deepen the spring pockets as you'll end up breaking through into the port.
Find some decent springs, T140/lateT120 ones are OK.

Last edited by NickL; 10/02/20 11:48 pm.
Joined: Feb 2018
Posts: 179
Likes: 7
T
Britbike forum member
OP Offline
Britbike forum member
T
Joined: Feb 2018
Posts: 179
Likes: 7
All of the valve work I felt was outside my skillset. I farmed them out to Eric Colvin in Oklahoma City. Eric is a vintage bike mechanic, used to race flat track, etc. One of the original valves was bent, seats were corroded. I don't remember if the guides were replaced. I know the seats were freshened. He used Kibblewhite valves and springs. And I remember he said the valves are standard dimensions. Expensive lesson in valve train geometry.

Joined: Jan 2014
Posts: 1,030
Likes: 56
N
Britbike forum member
Offline
Britbike forum member
N
Joined: Jan 2014
Posts: 1,030
Likes: 56
If the valve was bent, chances are it hit the piston.
I would be checking cam timing as there's normally loads of clearance on a standard a65.
Has the head or barrel been skimmed?
P+M make good gear, are you sure the valves are standard size? they do oversize ones as well,
they require the seat cutting back a bit..

Last edited by NickL; 10/03/20 12:38 am.
Joined: May 2013
Posts: 7,237
Likes: 53
Britbike forum member
Online Happy
Britbike forum member
Joined: May 2013
Posts: 7,237
Likes: 53
As Nick says, it’s time to check the valve timing. Sadly just looking at the dots and dashes on the cam wheels isn’t enough. I have a crank pinion which advanced the timing by 20° (with the timing advanced the inlet valve was closed before TDC so it would never have connected. If your setup is letting your timing be retarded by a similar amount of degrees then your valves will dink on the tops of your pistons.
To add to this, if your using the standard cam and your cam follower radius is greater than the standard 1.25” or worse flat, then your valve will hit the piston again. If these are showing any wear, get a machine shop to re-grind them. Also if your springs have been binding, these follower faces will have taken a battering and you should lift the barrel and inspect them. If you can, post a photo of them here.

As per your last post, I’d recommend not to shim the valve springs and to get them from Ed V. As others have said there’s too much junk on the market.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Joined: Mar 2020
Posts: 47
Likes: 1
R
Britbike forum member
Offline
Britbike forum member
R
Joined: Mar 2020
Posts: 47
Likes: 1
Here is a picture of the first set of springs I installed on my 71 Thunderbolt. They had coil bind on the intake valves. I replaced them with a set from CBS. There springs have 1 les coil than the first set. They have information about the springs on there web site. Hope this will be helpful.

Attached Images
20200509_111431.jpg
Joined: Jan 2014
Posts: 1,030
Likes: 56
N
Britbike forum member
Offline
Britbike forum member
N
Joined: Jan 2014
Posts: 1,030
Likes: 56
Ahhhh, i remember this thread when it came up.

You put a set of cbs's springs in and they say they measure them at the shop so i don't think
the problem is valve springs. Plus subsequently you said the other springs are pm, their gear is
very good.

You are bending valves so they must be hitting the pistons. Any evidence when you had the head off?


Moderated by  Allan G, Jon W. Whitley 

Link Copied to Clipboard
Upgrade to: Premium Membership | Gold Membership | Life Membership | Vendor Membership | Site Sponsor Membership

BritBike SponsorBritBike Sponsor
Home | Sponsors, Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons, | DVD- Manuals & Parts books














Powered by UBB.threads™ PHP Forum Software 7.7.5