horrible engine noise (2008)

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johnny 750

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hello everyone. some of you have helped me out with rebuilding my dads 72 commando 750, and i've been checking on this site for tips and insight, since this was the first bike i've ever built from a basket case.

the engine is making a funny clicking noise that my dad says wasn't present when he took it apart more than 15 years ago (sadly he has no time to really help me with the bike). i set the timing statically and it seemed fine. the rockers and valves are adjusted. the noise seems to be coming out of the engine head, but it's hard to say. i'm not familiar with the natural noises that these engines make, and i'm not sure what i'm listening to . with a strobe, it timed at 28 at idle, and then more like 35 at 3000 rpm (as the manual suggests, it should be 28 at 3000 rpm).

i filmed the bike and noise so that you all could hear it and perhaps help with a diagnosis. any help or input would be greatly appreciated.

http://www.youtube.com/watch?v=9sJyxm-CHok

there is the link. thanks!

johnny
 
johnny 750 said:
with a strobe, it timed at 28 at idle, and then more like 35 at 3000 rpm (as the manual suggests, it should be 28 at 3000 rpm).
Click to expand...


The video clip shows your bike is fitted with a Lucas Rita electronic ignition. You should set that to 28 degrees BTDC at 6-6,500 RPM, do not follow the manual instructions for points ignition.

Rita instructions: http://britcycle.com/Manuals/333100RitaInst.pdf
 
Sounds like a lot of Commandos mine included. Always seems worse indoors with the noise echoing off walls. If it's Combat spec the bigger valve clearance will always give a very rattly sound. Mine is probably due to worn lifters (tappets) being sloppy in the barrel (not the stellite foot).
 
SHUT IT OFF!

That's a bit too much tapping.

You say you checked the valve lash, so rule out misadjustment if you are SURE.

It sounds mechanical, not spark related (advance) if you ask me.

Definitely pull the timing cover and check the camchain, as was suggested.

If it's adjusted snugly, you may need to yank the top end and have a look.

You can always start with just the head. Hopefully it's contained to that component, if not, you can still have a look at your pushrods as well.

Next will be the cylinders, pistons, connecting rod small ends and cam followers.

I doubt you'll have to dig deeper than that.
 
It certainly does seem to be some kind of valve gear noise?

Something is either badly worn or very slack somewhere?
 
It sounds very regular , so not just one valve -pushrod- tappet .
Sinc you have no mechanical advance : remove plugs , select 4th gear .rock engine a little forward and backwards , while holding a finger on the ignition trigger . this may give you an indication of exessive slack in the camchain .
My bet : loose camshaft chain tensioner .
( BTW : exellent idea to film it !)
 
Possibly a loose valve guide?
Good idea to film / record sound.
Good luck. James
 
wow, thank you for all the suggestions. i bought some timing cover gaskets off ebay so i can get in there and take a look. i seem to remember having the chain tensioner all the way up when i put the cam chain in, so it was probably too slack in the first place as most of you have suggested, and i just didn't realize. i had the opportunity to go to raber's in san jose today and get a new cam chain, so i've got one. i actually had the top end apart last weekend, and the cam followers and push rods looked good. there was no unusual wear on the valves or pistons, both of which i replaced during the rebuild. i guess i'll replace that chain, and get the timing right according to the lucas rita instructions (thanks for letting me know about that btw :)) and i'll see how it runs after that...

thank you everyone! i very much appreciate all the input :)
 
You might want to expand the list a bit: also be needing a NMT 272 fresh donut seal for the oil pump and maybe an 04-8023 oil seal in timing cover and a 03-4053 points seal. Maybe a 06-1093 wire lead seal they are cheap. I would be picking up a auto cam chain adjuster and making a plan to true and check the oil pump. More gaskets, sand paper. Up to you but it is old.
 
AH!

I must have missed the part where you just did work on the top end.

Was it not making that noise before you did whatever work you did?

You MAY eventually need to disassemble it back to the lowest point you had it and then read, re-read and re-re-read the book as you SLOWLY re-assemble it with the new parts you've got coming.

Hopefully the new camchain cures the noise.
 
Maybe stupid...but it sounds like the head and valves are getting no oil....oil pressure or pump? Or are you running some really thin oil perhaps? Could the rocker shafts be in wrong, blocking off the oil, or something else blocking the oil passages?
 
Hi Johnny

try to locate the noise, simply way: Take a bigger screw driver, hold the metall end to the part of engine you want to listen. Lay your ear on the grab ( it's like uncle doc's stethoskop ). Go everywhere you think it's comming from.
To locate valvetrain noise, set valve lash at half of the recommended valve lash, but please don't drive or run it for a longer wile, your valve and seats say "thank you".
To locate piston rattle, worn bearings from rods and crank, disconnect the ignition wire from one cylinder, a second person hold the rpm's steady. If something is worn, the noise get away.
28 degrees ( what's factory?) initial ignition sounds like to much, ( you didn't broke your leg until now ? ) i would set it between 10 and 20 degrees. I f you have worn springs in your distribtor, the timing wont retard at idle !

Good luck
Marco
 
4onthefloor said:
28 degrees ( what's factory?) initial ignition sounds like to much, ( you didn't broke your leg until now ? ) i would set it between 10 and 20 degrees. I f you have worn springs in your distribtor, the timing wont retard at idle !
Click to expand...

Marco,

There is no auto advance unit, so no "distributor" springs, and no points, as this bike has a Lucas Rita electronic ignition system with electronic advance (see Johnny's video clip and my initial reply).
 
@L.A.B.
You're right, i'm sorry.

The rita instruction manual say's 20 degrees @2000rpm, but however it does not sound like pre-ignition pinging.
Have you got a endoskop near by you ? then try to watch through the plug hole into the cylinder ( piston hit head, valve hit piston o.e. )
Check also for loosen/broken adjuster screws, broken valve springs...

Marco
 
when I heard your motor I had a 1982 flashback. I was in a rush that day putting my head on. When I started the motor it made that exact sound.I immediatly took all valve covers off and looked inside the head with a flashlight, sure enough one of pushrods was not seating in the rocker arm. No need to take head off just loosen head bolts enough to seat properly, then retorque(loosen valve adjustment first.
 
Flashbacks are cool

mcns said:
when I heard your motor I had a 1982 flashback. I was in a rush that day putting my head on. When I started the motor it made that exact sound.I immediatly took all valve covers off and looked inside the head with a flashlight, sure enough one of pushrods was not seating in the rocker arm. No need to take head off just loosen head bolts enough to seat properly, then retorque(loosen valve adjustment first.
Click to expand...

Hey, I'm with you, I had a 1987 flashback when my T100C seized a valve in stopped traffic. It bent a pushrod. Same noise. What a racket though! I thought I now had a diesel. Could a pushrod be hanging up on a gasket, etc?
 
noise

sounds like pushrod noise to me my first norton had same kind of noise the engine blew up shortly after purchase not familar with the normal sounds of a norton I had no idea the machine blew up within a few hundred miles of running turned out pushrods were not all the same length one rod was slightly longer than the rest I had no idea and drove it till it blew then discoverd the reason for the odd noise from the head
 
johnny 750 said:
hello everyone. some of you have helped me out with rebuilding my dads 72 commando 750, and i've been checking on this site for tips and insight, since this was the first bike i've ever built from a basket case.

the engine is making a funny clicking noise that my dad says wasn't present when he took it apart more than 15 years ago (sadly he has no time to really help me with the bike). i set the timing statically and it seemed fine. the rockers and valves are adjusted. the noise seems to be coming out of the engine head, but it's hard to say. i'm not familiar with the natural noises that these engines make, and i'm not sure what i'm listening to . with a strobe, it timed at 28 at idle, and then more like 35 at 3000 rpm (as the manual suggests, it should be 28 at 3000 rpm).

i filmed the bike and noise so that you all could hear it and perhaps help with a diagnosis. any help or input would be greatly appreciated.



there is the link. thanks!

johnny
Click to expand...



Hi,
Did you ever figure out what was wrong with the engine.
Cheers,
Joe68
 
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