ashman
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Mine blew at 12000 miles not kms.
Tappety Noise
- Thread starter Fastback-DE
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Fastback-DE
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Hi again,
I've reconditioned the gearbox with new bearings and bushings (two of the bushings were pretty knackered), and started putting the bike together again. However, I then decided to try turning the engine with a crank, without the primary and gearbox connected, and guess what.... there is still a "dock-dock" noise....
It occurs at exactly the same position, every two turns of the crank, so it must be something cam-related. There is nothing suspect under the timing cover, so I suppose I'll start pulling the head and cylinders...
Cheers
Esben
I've reconditioned the gearbox with new bearings and bushings (two of the bushings were pretty knackered), and started putting the bike together again. However, I then decided to try turning the engine with a crank, without the primary and gearbox connected, and guess what.... there is still a "dock-dock" noise....
It occurs at exactly the same position, every two turns of the crank, so it must be something cam-related. There is nothing suspect under the timing cover, so I suppose I'll start pulling the head and cylinders...
Cheers
Esben
Before you remove the head, Take off the valve covers, so you can see if there is any erratic movement as the vales open and close, You could put a finger on each rocker arm as it travels the full range of motion to feel or hear any change in the sound,.
Just taking things apart "blindly" can hamper finding a solution. Once I had a strange noise in my MK3, Lucky I tracked it down to a bent tach drive gear. Without me being lucky or clever or both , I could have taken the engine apart and never figured it out.
Have a helper turn the engine back and forth at the place where the dock- dock is and go around the engine with a listening device and track the location down.
Just taking things apart "blindly" can hamper finding a solution. Once I had a strange noise in my MK3, Lucky I tracked it down to a bent tach drive gear. Without me being lucky or clever or both , I could have taken the engine apart and never figured it out.
Have a helper turn the engine back and forth at the place where the dock- dock is and go around the engine with a listening device and track the location down.
Fastback-DE
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I did check various things first, including the tach drive, but then pulled the head and barrel.
The LH piston must have seized at one point, because it's completely toast. The RH looks almost brand new....
Also, it's 74mm, so max oversize.
Oh well, new barrels and pistons it is.
On the positive side, the engine does have Carillo rods!
Cheers
Esben
The LH piston must have seized at one point, because it's completely toast. The RH looks almost brand new....
Also, it's 74mm, so max oversize.
Oh well, new barrels and pistons it is.
On the positive side, the engine does have Carillo rods!
Cheers
Esben
Fast Eddie
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Jim Schmidt does 74.5mm forged pistons for standard length rods. Choice of CR too…
Complete set of two forged Norton lightweight flat top JE forged pistons 750 to 1007cc for stock Norton rods.
norton pistons and stock rods
jsmotorsport.com
Last edited:
trident sam
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My mate had one , it was a beautiful car , I always wanted it but he wouldn't sell. I ended up with a Lancia HPE (with no rust !) that was a great car for me
could you have engine pinging instead of something loose I've just developed a similar noise on my 71 750 roadster. I'm checking my timing and if that is OK i will drop the fuel and refuel with some octane booster. At the moment Australia is accepting fuel from anywhere in the world and may not be the same quality as we are used to.
Shelby-Right
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Your forged pistons likely, 4032 will have more clearance,than cast these are good though.
Fastback-DE
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Yes!
I put in new (well, barely run) pistons and block, and the noise was gone. Note, was....
It just seized again!!!
Exactly the same situation, 5 minutes or so at 4000rpm, loss of power and knocking.
Oh dear...
Fastback-DE
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Hi again,
Im obviously going to pull the engine again, but I'd like to understand what went wrong (twice).
Mixture too rich, washing off the oilfilm?
Mixture too weak, causing overheating?
Something with the oil supply? I've got very healthy oil pressure - 3.5bar or so - but I've read that blocked sludge traps can block the oils supply for the left piston.
Any ideas?
Im obviously going to pull the engine again, but I'd like to understand what went wrong (twice).
Mixture too rich, washing off the oilfilm?
Mixture too weak, causing overheating?
Something with the oil supply? I've got very healthy oil pressure - 3.5bar or so - but I've read that blocked sludge traps can block the oils supply for the left piston.
Any ideas?
marinatlas
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What was the tolerance for your forged piston vs the barrel ?
Triton Thrasher
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I think a very rich mixture would have shown up as a performance problem.
Too weak is a common cause of seizures. Can be instigated by insufficient fuel flow or needle height set weak or small main jet.
Anything that can cause detonation can cause a seizure. That could be ignition timing or low grade fuel.
Insufficient piston to bore clearance seizes many people’s old bike engines nowadays.
Too weak is a common cause of seizures. Can be instigated by insufficient fuel flow or needle height set weak or small main jet.
Anything that can cause detonation can cause a seizure. That could be ignition timing or low grade fuel.
Insufficient piston to bore clearance seizes many people’s old bike engines nowadays.
marinatlas
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Today I heated up some cast iron cylinders and a lightweight piston to check what happens to the clearances when things warm up.
TEMP measured with lazer temp reader:
JE Forged pistons grow .007” in diameter from 75 to 250 deg
They grow .008” from 75 to 290 deg
Cast iron cylinders grow .002” from 75 to 250 deg
They grow .003” from 75 to 280 deg
Yes pistons get hotter - but these are the specs I'm showing today (mind you this was a spur of the moment idea after seeing my wife pull breakfast out of the oven).
Oven heated piston below measured with lazer temp reader
...
TEMP measured with lazer temp reader:
JE Forged pistons grow .007” in diameter from 75 to 250 deg
They grow .008” from 75 to 290 deg
Cast iron cylinders grow .002” from 75 to 250 deg
They grow .003” from 75 to 280 deg
Yes pistons get hotter - but these are the specs I'm showing today (mind you this was a spur of the moment idea after seeing my wife pull breakfast out of the oven).
Oven heated piston below measured with lazer temp reader
Fastback-DE
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I'm not sure what the tolerance was, but i bought the piston/barrel combination from one of the specialists here in Germany.
I'll definitely have a very close look at the carbs, and probably also split the crank case this time.
I'll definitely have a very close look at the carbs, and probably also split the crank case this time.
Fast Eddie
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Strip the carbs and check what’s in there, inc needle position etc.
If you were crushing at 4k rpm you could have been holding a steady throttle position that was lean, ie the needle was too low, or similar ?
Were the replacement pistons forged or standard or what?
If you were crushing at 4k rpm you could have been holding a steady throttle position that was lean, ie the needle was too low, or similar ?
Were the replacement pistons forged or standard or what?
