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I have 1996 evo just put new high compression pistons and Andrews high lift springs #294150 (up to .550 lift) I have S&S 520 cam. First time firing bent the front exhaust pushrod idling for 3 mins replaced all pushrods with S&S quickees. Fired the second time and rear exhaust pushrod bent. I have hydraulic lifters and adjusted pushrods 2.5 turns vs the 4 they call for just to be sure I didn’t bend them. Everything in rocker boxes looks good as does cam. Could the new springs be too stiff?
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Motors bend pushrods because somethin' is hittin' somethin' it ain't supposed ta hit. PERIOD.
Taking high rpm valve float out of the equation, because you ain't copped to that, that leaves a few options:
1) The spring pack does not have enough travel for the cam lift, and it is coil binding.
2) The free travel of the valve (distance from the top of the guide/seal to the bottom of the top spring collar) is insufficient and the top collar is hitting at full lift.
3) The valve to piston clearance is insufficient for the cam lift, and the valve is hitting the piston.
4) Valve to valve clearance is insufficient, and the valves are hitting each other in overlap, although this usually bends the valves.
I've said this many times, and will repeat it here:
Cylinder head set-up is THE MOST OFTEN FUCKED UP PART OF MOTOR BUILDING. This is true even in shops with professionals who KNOW BETTER, but don't take the time to do the job PROPERLY.
I fix two or three sets of heads a year that were improperly done by people who (should) know better.
Jim -
It's coil binding.... Did you check before you started the bike???Comment
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Thanks Jim! I’m thinking #2 as well although I don’t quite understand completely how to fix that.. I have checked everything else you posted before no valve damage and no piston damage and it is the same valves bike has been running for years fine just wanted to beef it up a little.. I still have stock springs I can put back in butt don’t really want to after all this...Comment
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Not coil binding I did check before starting ...Comment
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The Andrew's springs are a nice little upgrade for short money.
You can bump the guides down .06, or 1/16" to gain some extra clearance, but you need the proper collar for a guide punch, so you are hitting the shoulder of the guide rather than the end. (I made one up for myself with this extra .06 built in.) You can also cut a small amount of the top of the guide, .02 or .03, for a little more clearance.
JimComment
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Take my 45 and outrun em all ..Comment
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Do you know if the heads have the original 1.625:1 ratio rocker arms?
Could be that higher ratio than the stock '84 - 2000 Evo rocker arm have been installed, such as the Ultima 1.675 and 1.690; Crane Cams 1.725; and JIMS 1.745 ratios.
These will create higher valve lift and could be part of the reason for the interference issue. S&S states: "A minimum clearance of .060" must be maintained between the top valve spring retainer and the valve guide or valve seal when the valve is completely open."If buildin' old school choppers was easy, anyone could do it... ain't nobody said it's gonna be easy...Comment
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First thing I thought was...
Is he adjusting the pushrods properly?
Second, are the solid conversions pumping up?
Then, the clearances "should" have been checkedComment
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It was coil binding BTW in a way I didn’t replace the bottoms collars and the inner spring wasn’t seating properly.. put stick springs back in and been riding all summer thanks guysComment
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