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
Welcome to BritBike Forum!
Member Spotlight
tridentt150v
tridentt150v
Great Southern Land
Posts: 1,235
Joined: September 2001
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
Joined: Feb 2018
Posts: 179
Likes: 7
T
Britbike forum member
OP Offline
Britbike forum member
T
Joined: Feb 2018
Posts: 179
Likes: 7
I took my Thunderbolt out yesterday for its first shake down run after setting idle for 35 years. I find it a little ironic that both this bike and I have sat for that long. I started the engine and got it to settle down to a reasonable idle. I started going around the block, nice and easy at first, then hard acceleration followed by hard deceleration. I'm running SG 30 W. I was thrilled by the sound and torque. Very strange after not riding for long. At low speed the steering felt heaver than I remember my Norton. My right foot did better at shifting than my left did at braking. More work needed there. However there were issues. Some more serious than others. Much advice is needed.

1. RPM was self limited. Idle and mid circuit seemed ok, but at about half throttle when the main kicked in it would pop and shut down gas starved. Back off the throttle and it would come back to life. It's a new AMAL Premier, I assume the float level needs attention.

2. Transmission: It shifted solidly into first and second. Nothing for third and fourth. When I lifted the shift lever there was nothing, like it wasn't even trying to engage. But when I returned to the garage, on the stand, engine off, and turning the kick lever I could engage all four gears. I don't even know where to start with that. Any and all advice is appreciated.

3. Top End. After riding around the block several times I gained the confidence to venture out on a side road that has more hills. Again I was pulling up the hills and decelerating hard on the down side. On the last trip out I noticed a considerable increase in top end noise and started heading back home. I was about a half mile from the house. As I topped the small hill into my neighborhood the top end noise became quite loud, and I put the new kill switch to immediate use and coasted the 1/4 mile into the garage. Today I dropped the sump plate and found swarf. Upon removing the valve cover I found the intake rockers all jacked up.
[Linked Image from i.postimg.cc]
[Linked Image from i.postimg.cc]

When I tried to loosen the drive side rocker, it broke off. Further disassembly revealed one bent rod,(drive side), and one severely scored rod on the timing side.
[Linked Image from i.postimg.cc]
[Linked Image from i.postimg.cc]

What happened? What went haywire?
What do I need to do other than replace the obviously damaged parts?

A setback indeed. BUT IT RAN!!!!

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: Sep 2013
Posts: 2,868
Likes: 68
Q
Britbike forum member
Offline
Britbike forum member
Q
Joined: Sep 2013
Posts: 2,868
Likes: 68
Is it the intake side that broke ?
i suspected a valve made contact with a piston ... that's why the acceleration was limited

( I hope I'm wrong )

Last edited by quinten; 08/25/20 12:59 am.
Joined: Feb 2018
Posts: 179
Likes: 7
T
Britbike forum member
OP Offline
Britbike forum member
T
Joined: Feb 2018
Posts: 179
Likes: 7
Intake, yes.
Until I know more I'm convinced the limited RPM was fuel related. It was too repeatable. I think I would have heard piston banging valve.

Through out the run I was listening intently. The engine really sounded pretty darn good. Top end noise was less than I remember from my T140, about the same as the Norton I'd say. Right up until it wasn't. The top end noise came on quickly and progressed rapidly.

Joined: Aug 2001
Posts: 5,494
Likes: 76
Britbike forum member
Online Content
Britbike forum member
Joined: Aug 2001
Posts: 5,494
Likes: 76
Originally Posted by Tracey Spear
I'm running SG 30 W. At low speed the steering felt heaver than I remember my Norton.

1. RPM was self limited. Idle and mid circuit seemed ok, but at about half throttle when the main kicked in it would pop and shut down gas starved. Back off the throttle and it would come back to life. It's a new AMAL Premier, I assume the float level needs attention.

2. Transmission: It shifted solidly into first and second. Nothing for third and fourth. When I lifted the shift lever there was nothing, like it wasn't even trying to engage. But when I returned to the garage, on the stand, engine off, and turning the kick lever I could engage all four gears. I don't even know where to start with that. Any and all advice is appreciated.

3. Top End. After riding around the block several times I gained the confidence to venture out on a side road that has more hills. Again I was pulling up the hills and decelerating hard on the down side. On the last trip out I noticed a considerable increase in top end noise and started heading back home. I was about a half mile from the house. As I topped the small hill into my neighborhood the top end noise became quite loud, and I put the new kill switch to immediate use and coasted the 1/4 mile into the garage. Today I dropped the sump plate and found swarf. Upon removing the valve cover I found the intake rockers all jacked up.
[Linked Image from i.postimg.cc]
[Linked Image from i.postimg.cc]

When I tried to loosen the drive side rocker, it broke off. Further disassembly revealed one bent rod,(drive side), and one severely scored rod on the timing side.
[Linked Image from i.postimg.cc]
[Linked Image from i.postimg.cc]

What happened? What went haywire?
What do I need to do other than replace the obviously damaged parts?

A setback indeed. BUT IT RAN!!!!

Why are you using SG30W?, recommended lub oil is straight 40 or 20/ 50,.
30 W is for the depth ofWinter.
Heavy steering, check front tyre pressure.

Problem 1 may be linked to the mechanical carnage, might just be waterin the fuel, if it starts and runs its not the float level, why are USA peeps obsessed with float level? Check your fuel flow from the taps, drain float bowl into a divining bowl look for dirt and water.
Bear in mind that 90 % of carb faults are lectric, it might be as simple as a bad crimp in the ignition circuit that shakes to fail at high revs.


Problem 2.
The gear shift is failing to reset after changing into 2nd, the return spring needs tweeked.

Problem 3, Dearie dearie me, ochone ochone, I suspect one of the pushrods was not correctly seated on the cam follower, or may have been bent on installation, at high revs it jumped out of position, hence the carnage. Either that or a valve collided with a piston, irresistible force meets immovable object, rocker arm breaks, either way , examine piston tops and check valves are not bent.
Best of luck


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: Dec 2002
Posts: 664
Likes: 3
M
Britbike forum member
Offline
Britbike forum member
M
Joined: Dec 2002
Posts: 664
Likes: 3
Originally Posted by gavin eisler
Why are you using SG30W?, recommended lub oil is straight 40 or 20/ 50,.
30 W is for the depth ofWinter.
Heavy steering, check front tyre pressure.
I think he's referring to 30W fork oil

Joined: Dec 2002
Posts: 664
Likes: 3
M
Britbike forum member
Offline
Britbike forum member
M
Joined: Dec 2002
Posts: 664
Likes: 3
Originally Posted by Tracey Spear
1. RPM was self limited. Idle and mid circuit seemed ok, but at about half throttle when the main kicked in it would pop and shut down gas starved. Back off the throttle and it would come back to life. It's a new AMAL Premier, I assume the float level needs attention.

2. Transmission: It shifted solidly into first and second. Nothing for third and fourth. When I lifted the shift lever there was nothing, like it wasn't even trying to engage. But when I returned to the garage, on the stand, engine off, and turning the kick lever I could engage all four gears. I don't even know where to start with that. Any and all advice is appreciated.

3. Top End. After riding around the block several times I gained the confidence to venture out on a side road that has more hills. Again I was pulling up the hills and decelerating hard on the down side. On the last trip out I noticed a considerable increase in top end noise and started heading back home. I was about a half mile from the house. As I topped the small hill into my neighborhood the top end noise became quite loud, and I put the new kill switch to immediate use and coasted the 1/4 mile into the garage. Today I dropped the sump plate and found swarf. Upon removing the valve cover I found the intake rockers all jacked up.

I think 1 and 3 are highly likely to be related. There was definitely something wrong with valve geometry and it's going to impact all sorts of things.

Gavin is right on #2. I bet if you just barely touched the top of the shifter after going into 2nd, it would have shifted to 3rd fine. Setting the spring a bit tighter should address that, though it's going to be almost impossible to test in the garage.

Joined: Feb 2018
Posts: 179
Likes: 7
T
Britbike forum member
OP Offline
Britbike forum member
T
Joined: Feb 2018
Posts: 179
Likes: 7
The use of SG 30W is based on a recommendation in Mike Brown's "Building Budget Brits. He states " I was also taught to use 30-weight non detergent oil for break-into promote a good ring seal and Ifind that this works very well. If you decide to use this thinner oil. you must keep to shorter runs and moderate speeds until you switch to a thicker oil"

After thinking about it more, it seems that there almost had to be piston/valve contact, or the rod wouldn't be bent so.

Ah the neophyte engine builder blues. facepalm

Joined: Nov 2012
Posts: 1,768
Likes: 31
K
Britbike forum member
Offline
Britbike forum member
K
Joined: Nov 2012
Posts: 1,768
Likes: 31
Hi, just a few observations/thoughts.

The top rim of the driveside pushrod cup shows severe damage. The timingside one looks like it may be similar, but the pic is unclear. I can only imagine 2 ways for this to happen:
1) the rocker geometry is so awry that the pushrod rim contacts the rocker at top or bottom of valve lift. This could be wrong length pushrods, wrong length valves.
Looking at the adjuster on the broken arm, most of its spare threads seem to be on the nut end, this may hint in this direction.
2) the pushrods were assembled to the rocker balls such that they were perched on the rod rims (possible but I find it hard to believe, especially if both rods show similar damage at the top rim). Also if this were the case, I would expect the adjusters to be in an even more extreme setting than the one I can see.

The inlet pushrods have obviously been chafing against something. That is most likely to be the exhaust pushrods, though I am not familiar enough with the A65 to know how close the rods are to the tunnel.

Unless the broken rocker is an amazing coincidence, it is indicative of unusual stress on the arm.
Do the rockers move freely on the spindle? ie not seized.
There seemed to be a huge gap between pushrod cup and rocker in the pics. I think this is most likely because the valve(s) is jammed in its guide(s), in a partly open position.
The valve(s) could be seized in the guides through insufficient clearance (I think unlikely on the inlets), more likely the valves are bent.
I think the head must come off to determine the facts, unfortunately.

Why is another matter. I would suspect cam timing primarily, causing inlet valve/piston clash, which you are already thinking.

Best of…

Joined: Sep 2004
Posts: 1,417
Likes: 48
Britbike forum member
Offline
Britbike forum member
Joined: Sep 2004
Posts: 1,417
Likes: 48
My guess is that after 35 years of no use the valves have become partially seized in the guides as Koan suggests.

Although the bike initially started and ran after a short while, one or more valve(s) became stuck open and hit a piston. The pushrods later became bent whilst trying to open a valve which was hitting a piston.

Not a complete disaster but remove the head, check for any other to the pistons, check the valves are not bent, replace pushrods & rocker, rebuild and enjoy.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Joined: Feb 2018
Posts: 179
Likes: 7
T
Britbike forum member
OP Offline
Britbike forum member
T
Joined: Feb 2018
Posts: 179
Likes: 7
Originally Posted by gunner
My guess is that after 35 years of no use the valves have become partially seized in the guides as Koan suggests.

Although the bike initially started and ran after a short while, one or more valve(s) became stuck open and hit a piston. The pushrods later became bent whilst trying to open a valve which was hitting a piston.

Not a complete disaster but remove the head, check for any other to the pistons, check the valves are not bent, replace pushrods & rocker, rebuild and enjoy.

No, I've gone through everything. The head work I felt was out of my skillset and was farmed out. The valves were replaced to original spec. He even wanted the cam to make sure the springs were correct for the lift.

Until proven otherwise I have to assume builder error. Maybe clearance was tight on a guide an the valve suck. Time will tell I suppose.

It's a setback for sure, but I'm coming around to pulling the head and taking to Eric Colvin for evaluation. Once you've taken one completely apart and put back together, pulling the head isn't as intimidating as it once was.

In the mean time I better order some push rods and a rocker arm.

That short ride was great motivation.

Thanks all for the encouragement and sympathy.

Joined: Nov 2012
Posts: 1,768
Likes: 31
K
Britbike forum member
Offline
Britbike forum member
K
Joined: Nov 2012
Posts: 1,768
Likes: 31
I think you will likely see evidence of inlet valve/piston contact, which was slight when the engine was cold, allowing it to run as you found.
I would imagine the inlet valves to be increasingly bent as the engine warmed up, making the engine impossible to run at higher rpm.
Eventually the valves would be bent enough to jam part way in the guides.

The rocker arms and pushrods would have been under extreme duress while this was going on, so no surprise that one has broken and one bent.
That the inlet rods have been chafing against others illustrates how much bending they were tolerating before giving up the ghost. It does look like the upper cups were near failure as well.

We need to see what you find with head removal, but I still think cam timing is something to check.

Joined: Aug 2001
Posts: 172
Likes: 4
M
Britbike forum member
Offline
Britbike forum member
M
Joined: Aug 2001
Posts: 172
Likes: 4
and check the guides for cracks. especially if they are cast iron

Joined: May 2013
Posts: 7,241
Likes: 53
Britbike forum member
Offline
Britbike forum member
Joined: May 2013
Posts: 7,241
Likes: 53
I’ve used 30w running in oil with no problems. On a new motor where your probably not doing more than 10-20 miles on initial running in the oil still isn’t a it’s running temperature before you’ve stopped the motor again to let it cool down.

Before there’s an oil war you might find this Link interesting. I first found this site about 4 years ago and didn’t add it to my favourites. It’s a good read.



There doesn’t have to have been piston to valve contact to have bent the pushrod. A likely scenario is that the pushrod wasn’t properly seated on the cam follower... gap then set according to that and it all went to buggery from there. Something got jammed and caused the damage.

Last edited by Allan G; 08/25/20 9:21 pm.

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: Aug 2001
Posts: 5,494
Likes: 76
Britbike forum member
Online Content
Britbike forum member
Joined: Aug 2001
Posts: 5,494
Likes: 76
Let is know what you find, dont trust anyone else to build your head, valve spring compressors are handy, a decent rule will give fitted valve spring length, clean it and cleanit again.Valves dont normally seize, dirty build?

, for the first 50 miles after a rebuild my bike gets cheap supermarket oil, after that it gets good stuff, 30 W isnt the issue.Peace.

Last edited by gavin eisler; 08/25/20 11:09 pm.

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: Sep 2004
Posts: 1,417
Likes: 48
Britbike forum member
Offline
Britbike forum member
Joined: Sep 2004
Posts: 1,417
Likes: 48
Another possibility is that the valve springs are becoming coil bound at full lift which leads to the pushrods becoming bent as the cam tries to open the valve.

I actually had the same problem when I first built my A65 and had the head reconditioned. It turned out that the valve springs were made from thick wire and were getting coil bound on full lift. I was lucky and got away with just one bent pushrod but it took some investigation to find the cause.

Eventually I discovered that the valve springs were the wrong type and got some new ones with thinner wire from SRM.

Before you remove the head, try turning the engine over with some new pushrods fitted and check if the valve springs are coil bound or not.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Joined: Feb 2007
Posts: 2,592
Likes: 34
S
Britbike forum member
Offline
Britbike forum member
S
Joined: Feb 2007
Posts: 2,592
Likes: 34
Originally Posted by gunner
Another possibility is that the valve springs are becoming coil bound at full lift which leads to the pushrods becoming bent as the cam tries to open the valve.

I actually had the same problem when I first built my A65 and had the head reconditioned. It turned out that the valve springs were made from thick wire and were getting coil bound on full lift. I was lucky and got away with just one bent pushrod but it took some investigation to find the cause.

Eventually I discovered that the valve springs were the wrong type and got some new ones with thinner wire from SRM.

Before you remove the head, try turning the engine over with some new pushrods fitted and check if the valve springs are coil bound or not.

At full compression there should be 60 thousands between the spring coils to prevent damage to the head bits.

Ask me how I know....
mad

Joined: Jan 2014
Posts: 1,030
Likes: 57
N
Britbike forum member
Offline
Britbike forum member
N
Joined: Jan 2014
Posts: 1,030
Likes: 57
If the guy who did the valve guides does mostly water cooled gear he probably
had too little guide clearance, as the bike heated up, it's nipped the valves. Bingo.
It's unlikely the oil caused the problems, i raced an a65 using 30 weight oil for a
long time even over here in 40+ deg conditions.
When you re-do the head put a little grease on the pushrod tips as you put them
in and make sure you can lift the followers up and down, that way you'll know their
seated properly.


Moderated by  Allan G, Jon W. Whitley 

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