my fault i think (nock from the engine, crank end float)

[Mtrower]

just  joined and I am picking your brains my super rocket as she as run very well the 3 years well the last 3 summers ,had a problem with the carb throttle slide sticking when hot new carb body sorted that .The last meet at are local bike night on the way home I started to get a nock from the engine pulled over and on tick over it sounded fine ,set off and the nock was back.Did some checks removed the clutch cover checked the crank end float the book says no more than 5 thou I have got about 50.just removed the engine took the head of and found two head gaskets fitted waiting for the tool to arrive to remove the mag gear and I will the carry on stripping the motor .I believe the shims have let the side down on the drive side bearing .the bike had a full restoration 20 years ago it as just over 2000 on the clock 900 of them mine .Is there things to check when the engine is down and is this a fault oil changed every year and good oil pressure i do not want it to happen again its my wheels for the classic this year

[Billybream]

Clean the crank sludge trap, get crank end float below 0.003".
Replace check valve springs and balls.
Check bores for wear and rings for clearance.
Just check and clean and clean again.

[chaterlea25]

Hi,

is this a fault

Broken shims are most often caused by the bike being run with cush drive nut not tight
A resultant  problem can then be the drive side end of the crank gets worn where the inner bearing race fits
movement between the bearing and crank will "push" out the shims
A stack of thin shims is a bad idea, once the thickness is established a custom solid shim is the best.
Throw away the lockwasher on the cushdrive nut degrease the threads and use thread locking fluid
Tighten to 65ft/lbs

John

[Swarfcut]

   Sounds more like  the start of a big end failure...... Quiet at idle, knocks under load.
 Usual B/E  to fail is on the drive side, furthest away from the oil pump. With the barrel off, check for lift on the big ends...    some sideways movement is usual, in other words the pistons and rods will slop sideways, but there should be no up and down movement.

 At this stage you are probably best stripping the motor to its last nut and bolt, checking every oilway  and the all important sludge trap in the crank is clear. Plenty on the forum about this single most important and critical aspect of the design.

 Previous posts add other important  points that need attention. Check finance and credit score now.

 Swarfy.

 

[BSA_54A10]

   Sounds more like  the start of a big end failure...... Quiet at idle, knocks under load.
 Usual B/E  to fail is on the drive side, furthest away from the oil pump. With the barrel off, check for lift on the big ends...    some sideways movement is usual, in other words the pistons and rods will slop sideways, but there should be no up and down movement.

 At this stage you are probably best stripping the motor to its last nut and bolt, checking every oilway  and the all important sludge trap in the crank is clear. Plenty on the forum about this single most important and critical aspect of the design.

 Previous posts add other important  points that need attention. Check finance and credit score now.

 Swarfy.

Rule of thumb
Knocks on over run = BIG ENDS
Knocks on load = LITTLE ENDS

[Mtrower]

Thanks for the quick  reply took it out before  I took  the engine  out nock  was when you  accelerate  and shut off ,crush  drive  nut held  in place with split pin engine looks like new pistons. Fitted now plus 20 I assume  the two head gaskets  were to lower  compression. I have lots of info with the bike lots spent as a mate said the engine is only  as good  as the last man ho built  it.my mag puller  will be here Saturday  so will let you know when I know.i rebuilt  my plunger engine I know the sr is different  in a lot of ways.

[berger]

split pin is no comfort, I found my shims in the sump because the nut had undone very slightly allowing the crank to hammer the shims and spit them out. I was baffled by a big clunk every time it fired up and then found the shims,  I now have a lock nut I knocked up in the lathe out of another old crank nut that sits nicely in the recess of the original nut, no problems since. some people prefer srm nut and thread lock, good luck and i hope it is an easy fix.

[muskrat]

G'day Mt.
All of the above ^.
Full strip down time I'm afraid.
One thing that hasn't been mentioned is the con rods. Check for twist and squareness. This can cause undue big and little end wear that gives knocks and rattles.
Cheers 

[Swarfcut]

   G'day Musky.
    A well made and often overlooked point there concerning the con rods.

 As a general observation,  big end eyes also need to be checked for ovality.  The big end crank journals have a recommended max of  2 thou tolerance for ovality, so you can see any additional problem with the rods will add to this, let alone worn journals or flashed out shells.

 As to the source of the knock, anything that moves is a possible culprit. Small end bushes, piston bosses, cracked pistons, broken rings, piston slap, main bearings, big ends.
    '54 added to my initial comment, and there is a whole spectrum of noises which enable the well experienced to diagnose by ear with attention to throttle setting, load, over-run etc. Some symptoms are characteristic, but in any event looks like a pull down. Be interesting to see what you find.

 The problem fixes are the ones where everything looks normal. Major mechanical mayhem are the easy (if expensive) ones.

 Although we are all looking on the black side of things, just make sure there is nothing in the primary side that could be a simple fix.

 Cheers.

 Swarfy.

[Greybeard]

My understanding of that split-pin is, it's there to prevent a loosened cush-drive nut from gouging into the chain case. On my bike, (Plunger) there is a gap between the split-pin and the face of the nut.

[bikerbob]

On my 1956 swinging arm A7 I have a gap between the split pin and the nut I was not happy with that so I fitted washers to eliminate the gap, so now the split pin slides neatly over the washers.

[Swarfcut]

GB Quite correct. The plunger cush drive nut has a raised boss which bears onto the end of the drive sleeve. The sleeve should extend slightly past the crank splines, so the nut bears on the sleeve, not the splines. S/A nut is different, with a flat face and different drive sleeve. Several types were used, so care needed to be sure they are all the right bits. Principle is the same, and a gap will exist between the split pin and the nut. A washer here as bikerbob did is a belt and braces approach, nothing wrong with that. Loctite and a homespun peg spanner, plus a  hernia inducing tighten later, job's a good  'un.

 Hammer and punch have ruined many a cush drive nut. Oh, the innocence and naivety of youth. The nuts came undone because they were never put on tight enough.....we're looking at 60-70 Ft Lbs as a torque figure.

 Swarfy.

[JulianS]

A Peugot 405 lower ball joint socket fits the original type cush drive nut and can be had on Ebay in the UK for about £12 including post. Allows you to torque the nut and avoid the temptation to use a hammer and drift to tighten.

Photo show the tool and is with a NOS M20 type cush nut.

I use an SRM nut torqued as close to 60 ft/lbs as I can get and always use loctite on it.

[Mtrower]

thanks for the info i needed to tighten the crush drive nut up to get the split pin out srm nut on order ,total strip down of the engine in order bores are glazed silicon on all joints one rear engine mount stood had gone for a walk and another was getting ready chance to service the dynamo .the left pot is a lot blacker than the right .the bike ran well did use oil but not a smoker.the guy that built the engine had a good reputation in his day but the guy i got the bike off i spent the first month sorting his bodgeups.will put pics on when i figure it out

[Greybeard]

I bought the tool that SRM sell for that job. I've been using my air powered rattle-gun to tighten the nut.