Engine jamming up occasionally at exactly 28 degrees BTDC

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jesterday

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Ok, so I have a strange problem. I just got my bike put together, engine was turning over normally. But yesterday while kicking it over, it jammed up at 28 degrees BTDC. I put it in gear and rotated the tire backwards and it freed up. It also happened one other time. When it jams it is impossible to kick it over. What could cause this? The bike hasn't been started since 1985, I am just trying to get it going for the first time. (Waiting for an electronic ignition to come in, because my points plate is all messed up)

I know the gear box may not be put together correctly as I can only find first gear and neutral, bit I doubt that would cause an issue.

1971 Norton 750.

Any suggestions?
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

jesterday said:
I know the gear box may not be put together correctly as I can only find first gear and neutral, bit I doubt that would cause an issue.
Click to expand...

Sort that out first - you'll probably need more than 1st out on the road..... ?!
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

That is true. That is my plan for tomorrow.
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

Check the timing mark pointer, fouling on the rotor? If you have been playing around with the rotor, it could be spaced too far out?

Hope it is that easy for you?

Cheers Richard
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

stockie2 said:
Check the timing mark pointer, fouling on the rotor? If you have been playing around with the rotor, it could be spaced too far out?

Hope it is that easy for you?

Cheers Richard
Click to expand...

hhhmmmm....how would that stop the engine completely? Just curious, as it is completely possible since I have just assembled everything and I have had to redo a few things in the process as I am prone to doing stuff wrong the first, second and third times...
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

Did you have the head off?
If so then it sounds like a push rod wasn't seated in the lifter and the valve may have hit the piston.
If thats the case then the valve could bee bent now.
I know first hand.
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

Guido said:
Did you have the head off?
If so then it sounds like a push rod wasn't seated in the lifter and the valve may have hit the piston.
If thats the case then the valve could bee bent now.
I know first hand.
Click to expand...

That is possible as well, but When it jams up, it seems to be on the compression stroke with no valves open.

I will do some trouble shooting tomorrow, and bring my laptop so I can get further info for you guys.
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

jesterday said:
That is possible as well, but When it jams up, it seems to be on the compression stroke with no valves open.
Click to expand...

While one cylinder is on its compression stroke, the other one isn't !
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

Not suggesting that there isn't something wrong, but,
I think you'll find that many of us have had the same thing happen
at one time or another.
It's a Norton mystery, and has been spoken about on this Forum before.
I don't know the answer, but my engine certainly has done exactly that, but can't
remember when the last time was, hasn't done it for a while.
AC.
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

Did you happen to try to kick it over after it was jammed with the clutch pulled in, and still in neutral? If the kickstart lever moved freely then the engine is the problem. If the lever was still stuck, (in neutral w/clutch pulled in), then it's the trans. My money is on the transmission. Like AC mentioned, it's come up on my bike but it's been so long ago that I can't remember the details. I seem to remember something about the shift forks/cam being off somehow and it's trying to engage more than one gear at a time, locking the transmission.
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

Say what, do I smell an Ozzie cooperative spoof here?

I can't envision engine fault that dramatic yet that intermittent. Even if a loose push rod end down there, ain't no pushrod motion going on @ 28' BTDC with valves closed on compression stroke. Maybe a kink in timing chain or chink in oil pump drive. Kick rachet comes to mind but would need primary un hooked to isolate what hanging up. Maybe just pulling our collective legs on unsolved mystery like Bermuda Triangle which us native Miamian's know is just a UFO base down there doing it.
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

Do you know why bike sat since 1985?
Any chance this problem came up and the PO never looked into it.
My bike when I bought it five years ago had sat since 1977.
Sorta ran but hard start and funny rattling sound.
Valve adjuster had unscrewed itself after lock nut split and was on top of lifters!

My guess is gearbox.
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

It will kick over with the engine in neutral and the clutch lever pulled in.
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

I can't envision engine fault that dramatic yet that intermittent. Even if a loose push rod end down there, ain't no pushrod motion going on @ 28' BTDC with valves closed on compression stroke. Maybe a kink in timing chain or chink in oil pump drive.
Click to expand...

I think hobot might be on the right track here. Because it only happens at 28' seems like it could be timing related. Pull the timing cover and check all the gears and chain.

Bill G
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

Ugh, just flashed back on sorta similar hang up in Ms Peel. After throttle stuck to over 11,000 rpm a few seconds plus a few more over red line on slammed shut throttle ... smoke cleared enough in 20 sec to see head still on... She started right up and I rode on off in great depression at lost of power to spank 600's any moren, a few rides later I pulled into shed idling and heard a clink for instant lock up, ugh. Thinking the worse started the tear down with primary. When crank belt pulley removed a tiny side plate screw fell out between pulley and crank. That was all that had caused the jam. Cleared the Al gouge on case and loctited the screw back in and rode another 2000 miles before deciding she needed 920 to play with the current crop of balloon tire wonders. The lost of power after 4900 was from the cam chain's total slack after RMA cam tensioner wiped off.
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

jesterday said:
Ok, so I have a strange problem. I just got my bike put together, engine was turning over normally. But yesterday while kicking it over, it jammed up at 28 degrees BTDC. I put it in gear and rotated the tire backwards and it freed up. It also happened one other time.
Click to expand...

You mentioned that it happened one other time, so in between these times it was free. It's intermittent. You need to check it in the jammed condition. It would probably be easier if you pulled the primary cover and put a socket wrench on the rotor nut to turn over the motor, in the 'jammed' state, with the clutch pulled in.
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

It will kick over with the engine in neutral and the clutch lever pulled in.
Click to expand...

Ugh, this showed up while typing my long post so missed its Ring Dinger clue where to look first.
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

jesterday said:
I know the gear box may not be put together correctly as I can only find first gear and neutral, bit I doubt that would cause an issue.
1971 Norton 750.
Any suggestions?
Click to expand...
Actually, it looks like he's going to be giving the transmission a once over any way you slice it. Why not do it sooner rather than later?
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

Actually, it looks like he's going to be giving the transmission a once over any way you slice it. Why not do it sooner rather than later?
Click to expand...

Aw shush up, there's no savory away from home adventure tale in this advice?
 
Re: Engine jamming up occasionally at exactly 28 degrees BTD

Ok, I have the gearbox assembled properly now, at least I hope so, I can get first, neutral, second, and third. Not sure about 4th, but at least it seems to be working.

I haven't run into the jamming issue today. the timing seems somewhat normal, although my points are completely messed up and I can not get my gapping right because my adjustment screws are either broken or missing.

I hope I can get the carbs working properly, I think my throttle and air valve cables are mixed up. Oh my another time disassembling the carbs.
 
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