Slappy M944

Started by koko64, September 13, 2016, 06:21:20 AM

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koko64



An M944 came in with bad piston slap and a warped rear head which blew oil out towards the rear exhaust from the gas trail taking out the oil return O-ring. The sump plug is shown. I am about to tear into it and suspect the piston skirts have finally slapped through the Nikasil linings. The piston slap was louder than the clutch.
The rebore may have been mismatched to the hi comp 944 pistons although after 90,000 miles that's an unfair charge. The stock pinging ignition and warped oem engine studs (circa '94) are probably the culprits. [bang] It's amazing the studs didn't snap. The whole top end motor stability was compromised.
2015 Scrambler 800

ducpainter

I'd be surprised if you didn't find the L/H main bearing has failed and the 'slap' is the piston hitting the head.

AMHIK. ;)
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koko64

Thanks DP. So main bearing causing major piston rocking? There was certainly a clear slap rather than a knock to the motor. Should see inside soon. Interested in opinions as to the material.


An engine swap fixed things. New hotness, old busted in the background.
2015 Scrambler 800

koko64

Will a magnet grab Nikasil?
2015 Scrambler 800

ducpainter

"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."



koko64

Thanks. Shows how much I know about metallurgy. ;)

I'll post more pics once I open her up.
2015 Scrambler 800

ducpainter

You'd be surprised how much all those fins will change the noise.

Pull the left cover first.
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."



koko64

I'll open her up tomorrow.
Cheers.
2015 Scrambler 800

koko64

The little ends have been pounded by long term pinging (stock ignition on 944 hi comp) and the wrist pins and pistons were rocking laterally in the bore  nearly 5mm! The piston skirts were slapping the sides of each bore as evidenced by the scuff marks. How a piston didn't hole is amazing because they got hammered.
That material is still coming from somewhere, so I'll have the flywheel, etc off this arvo and see what's up. We'll see how the mains and big end fared.

Not fitting hi tensile studs allowed the engine platform to be insecure and this has warped the rear cylinder head. The oil return O-ring was damaged by a stray gas trail and oil was pissing out. The head material may be too soft now to be bothered re-machining and lapping it. A hardness test will confirm.

2015 Scrambler 800

Speeddog

Sounds like it's comprehensively rooted.  :-\
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koko64

2015 Scrambler 800

koko64

Further examination has revealed massive piston to bore clearance, both laterally and fore and aft. It exaggerated the wrist pin play. A mate said he has seen some bad overbore jobs locally and the pistons don't look as bad as the piston to bore clearance should suggest. Considering the mistakes made when this 944 was put together I'm starting to think the job was borne bad.
Oh well it's a spares motor now.
I haven't got the flywheel nut off yet. My rattle gun's rattled.
2015 Scrambler 800

koko64

2015 Scrambler 800

koko64

#13


Is that a Pistal?
2015 Scrambler 800

clubhousemotorsports

No that may be a Bucci or Gia.ca.moto.  they have not been used for quite some time.   what was the piston to wall? Any idea of the mileage on the pistons?  to do a 944 kit they had to have the cylinder bored and plated but there were "kits sold"  IIRC. One would hope it was made to fit at assembly but some drop in pistons are sold on the small side because the piston maker has no idea if the bike has an "A,B or C" spec cylinder.


The metal on the plug is from a bearing failure or the starter clutch probably. If you were hearing "piston slap" on a oil jacketed motor it must have been very  loose or Nate is right and it is a main bearing allowing the piston to touch the head. Any shiny spots on the tops of the pistons where the carbon has been knocked off?  It is NOT uncommon for big bores to warp the head between the rear studs due to the smaller sealing surface and higher temps/pressures.

The old studs were not weak as much as Brittle, this is the chrome studs only. It is actually lucky that they were still okay after the heads were off for the 944 kit, are you sure they are OEM?