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new motor knocks

3

3C Guiding

Well-known member
Dec 9, 2010
143
100
43
Laramie Wy.
Have a re built motor on a 04 summit 800 3 miles on it. Clutch side will knock when at idle but when we take the plug cap off that side when its running it will not knock any more so don’t think its inside the motor. We changed brain box with another sled still the same. Changed coils still the same, good compression, new fuel, and clean carbs. Any ideas will help.
 

byeatts

Well-known member
Premium Member
Nov 29, 2007
3,402
1,215
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Have a re built motor on a 04 summit 800 3 miles on it. Clutch side will knock when at idle but when we take the plug cap off that side when its running it will not knock any more so don’t think its inside the motor. We changed brain box with another sled still the same. Changed coils still the same, good compression, new fuel, and clean carbs. Any ideas will help.

primary clutch rebuilt? pretty common knock at idle at a certain rpm.
 
D
Dec 11, 2008
598
54
28
Livingston MT
depends where the knock is coming from. the pirmary or the cylinder? my primary knocks pretty bad at an idle. im sure its probably way out of balance, when you increase RPM's it goes away for the most part. did you try that?
 
S

sledsrock

Well-known member
Nov 26, 2007
1,826
510
113
Grand Junction, Co.
it was a rebuild crank. you think its a bent rod?

it is not in the clutch.

If you're sure it's not in the clutch and the knock goes away if you pull the spark plug wire off that cylinder.....what does that mean? Heck I don't know......does it knock when it's cold? does it do it whan it's warm? does it knock when rev'd up?

Big end rod bearing? Who did the rebuild? Where did you get the crank? Was the correct size wrist pin/bearing used? Pull the jug and start inspecting.
 
B

bikerjustin

Well-known member
Apr 14, 2008
364
45
28
Coeur d'Alene, Idaho
The spark jumping from a wire to a plug makes a knock when there is not a good connection. Check the wire and look inside the boot to make sure the wire end hasn't been pushed back into the boot
 

Ox

Snowest's Axe Murderer
Lifetime Membership
Premium Member
Jul 8, 2001
1,522
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113
NW Ohio
www.midwestproductionmachining.com
How have you ruled out the clutch?

Have you swapped clutches and tried it?

You may be able to get it to start/run w/o the outer half on. That would rule that out. Not sure how well it would idle tho. ???


.
 

wildcard28

Well-known member
Dec 18, 2007
1,477
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Clarkston WA
s375.photobucket.com
Maybe take the clutch off and start it, what pistons did you install MY 800HO HAS Wiseco pistons and they rattle when cold but gvoes away when warmed up

Does the sound get quieter when it starts to warm up of course if its pretty bad sound pretty sure don't want it to run very lomg. Pullv the jug off that side and chech for bearing and wristpin slop even how tight the piston is in the cylinder

Good Luck, wildcard
 
0
Jan 24, 2012
1
1
3
Turns out the crank spun out of phaze causing it to not fire at tdc and bdc so it was way out of time. Tore it appart had the crank trued and rewelded and its runnig great, thanks for all the suggestions
 
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