I recently purchased an 02 M750 with 16k miles on it motor is stock
there is a strange metallic knock sound when idling and revving engine when cold
as the engine warms up it goes away
looking to see if any one is familiar with this sound and how I would go about diagnosing it
I don't want to start tearing into it with out knowing what to look for
it seems more prominent when revving the engine the sound comes as rpms are coming down
here is a link to a video :
http://youtu.be/3i47cxLxsgo (http://youtu.be/3i47cxLxsgo)
Quote from: dansamp on August 27, 2011, 09:47:12 AM
I recently purchased an 02 M750 with 16k miles on it motor is stock
there is a strange metallic knock sound when idling and revving engine when cold
as the engine warms up it goes away
looking to see if any one is familiar with this sound and how I would go about diagnosing it
I don't want to start tearing into it with out knowing what to look for
it seems more prominent when revving the engine the sound comes as rpms are coming down
here is a link to a video :
http://youtu.be/3i47cxLxsgo (http://youtu.be/3i47cxLxsgo)
It's fin ring. Chances are your little hockey pucks have fallen out.
My 750 SS did the same thing.
edit
After listening again...
that's not fin ring [bang] [bang] [bang]
check the clutch nut too
DP's probably right, but I'd look at the flywheel nut and valve timing/adjust.
I always thought it was because the cold oil needed time to circulate through the system?
ok,
I am thinking it might be clutch noise
I have never had a wet clutch duc before
but I am thinking it might be the tangs in the basket have excess clearance
it does seem to be more pronounced at the right side
thanks for the input
The wet clutch is normally pretty quiet, and if the tangs were worn it wouldn't change when warm I wouldn't think.
It would be worth a look inside IMO.
Sounds like it runs at steady idle and up in rpm OK, but on dropping in revs it has that slapping sound, like once per revolution or something close to a low frequency like maybe once per two revs. So I ask, what runs at crank speed or half that. Anything attached to the crank or cams. Then I wonder what could have increased clearance when cold but closes the clearance when hot.
Since it is so distinct and on falling revs, I would use a stethoscope or even a long handled screwdriver and my ear tight to the handle end and probe the different parts of the engine. My bet is you will be able to hear it clearly in one place more than all the others. Then you could probably make the separation of the two heads and the common crank. If its still eminating from the crankcase area, then I would attempt to distinguish one side from the other. Once again, using the stethoscope or the poor man's stethoscope as the screwdriver and ear bone.
If you were more high tech, a guy might make a recording of the sonics and watch the file on a wav file graph with timing marks to see the frquency to the power pulses and maybe you'll gather important anaylsis of the connection between one cylinder and the other and the frequncy to the revs.
If I had to guess (and I just can't help myself) it almost sounds like good old fashion piston slap. But if that were it, its really loud to me and the noise is carrying well through the cases or its really worn out. I just can't connect a loose flywheel or clutch components as the culprit because it goes away when warmed up and its at a distinct frequency or cadence and I would think something loose would rattle at random or at least at a higher frequency.
thanks for the input
I will try the stethoscope/screwdriver and report back
while making the recording it seemed to be coming from
the clutch area to me , but that may just be wishful thinking
I agree it sounds like piston slap but the sound seems more
"hollow" to me
Quote from: 12gauge on August 29, 2011, 05:32:10 PM
...If you were more high tech, a guy might make a recording of the sonics and watch the file on a wav file graph with timing marks to see the frequency to the power pulses and maybe you'll gather important analysis of the connection between one cylinder and the other and the frequency to the revs...
12gauge, The recording and watching on a wav file graph seem easy and useful enough, but I'm a little bit confused over the timing marks. Is there an easy way to input ignition pulses into a laptop to use as timing marks or do you mean just using the built in software graph gridlines as timing marks? I'm pretty sure you mean the software graph gridlines but thought I'd ask.
Thanks,
Bob
ok,
this evening on the way home from work I stopped by a local shop I frequent
to get their opinion.
it looks like another vote for piston slap
so if that is the case, is it worth rebuilding/ building up a 750 motor
or should I find an 800 or 900 motor to swap out
or should I part the bike out ???
I see FBF sells hi comp pistons for about $400-$500
I have a full top from my previous '95 900 SS I wish there was some way I could use those parts ???
what to do !! ?? !!
I wouldn't rebuild it.
You'd do better to drop a 900 in there or another 750 with less miles...
or simply let it slap.
The 750's seem to clank when they're cold, the other sizes not so much.
IIRC, the web attributes it to forged pistons, which have a higher thermal expansion rate than cast pistons, so have to run more clearance.
If you wanted to open it up, you could fit some hi-comps, but I'm pretty sure all the aftermarket pistons are forged, so perhaps that wouldn't eliminate the slap.
750's run nice with hi-comps and 695 heads.
You would need to do a PCIII or the like as well, since you've got that one-year-only 750ie.
check flywheel nut, my 99 750 sounded like that..
nut was loose.
ok,
I tried the long screw driver to isolate the sound and could not hear it
if I stand back the sound is there more like a ringing
I noticed there are no pucks on the horizontal head and only about 3 on the vertical head
I don't think it is coming from inside the motor
I put the screw driver to the heads no sound
crankcase no sound
clutch cover no sound
stator cover no sound
but step back a foot with out the screw driver and you can hear it
??? ???
Quote from: Speeddog on September 03, 2011, 10:32:24 PM
The 750's seem to clank when they're cold, the other sizes not so much.
IIRC, the web attributes it to forged pistons, which have a higher thermal expansion rate than cast pistons, so have to run more clearance.
If you wanted to open it up, you could fit some hi-comps, but I'm pretty sure all the aftermarket pistons are forged, so perhaps that wouldn't eliminate the slap.
750's run nice with hi-comps and 695 heads.
You would need to do a PCIII or the like as well, since you've got that one-year-only 750ie.
what do you mean "one-year-only"???
tell me more about the 695 heads ???
I have some carby 900 heads maybe I could pull the cams out of those
would that give me more oompf ???
Quote from: dansamp on September 04, 2011, 01:58:18 PM
what do you mean "one-year-only"???
tell me more about the 695 heads ???
I have some carby 900 heads maybe I could pull the cams out of those
would that give me more oompf ???
They only produced the 750 as a fuel injected bike for the '02 model year. All the rest were carbies.
The problem with the 750 heads, as I understand it, is the shape of the combustion chamber as opposed to the cams although someone else may know of the benefits of the 900 cams in the small heads. The 695 heads have a better shape.
Quote from: dansamp on September 04, 2011, 01:58:18 PM
what do you mean "one-year-only"???
tell me more about the 695 heads ???
I have some carby 900 heads maybe I could pull the cams out of those
would that give me more oompf ???
2002 is the only year that the 750 was injected.
All previous years it was carbureted, and it was replaced by the 800 in 2003.
695 heads have larger valves (same as 800 and 900), better ports, and a better profile cam with more lift.
Not sure if you can use them to full effect with stock pistons.
Quite a bit of info here on 900 carbie cams in an injected 750:
http://www.bikeboy.org/750ss_900carb_cams.html (http://www.bikeboy.org/750ss_900carb_cams.html)