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Discussion Starter · #1 ·
Hey guys my engine builder milled .3mm of the head and now he said the valves were hitting the piston. Does this mean he didnt time it rite or wat.
Thanks
 

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something does not add up here, .3 MM is less then 12 thousands of an inch, unless my math is wrong, in no way should that cause that, he needs to go back and re-time the cams, not sure if the SX has a TDC bolt like the XC, (someone with a SX can chime in on that,) that could have moved or in the wrong place on the crank, or the engine rotated and he did not notice, re-time the cams and try again.
 

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Some one didn't do their home work. Measure twice cut once.
Did you put a high compression piston in? and 3mm thats like .070 thousands or more.
Did he put the crank stop bolt in to hold the crank at top dead center?
There is a flat grind on the cams at the back lobes and a tool to hold the cams at the right degrees
Bill
 

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Discussion Starter · #4 ·
I will find out more later i have a race sunday. Its exactly .3mm and stock piston.
 

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I checked my math and its .120 thats like a 1/8". Check to see if it is .3mm that he was to mill off
Bill
 

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I checked my math and its .120 thats like a 1/8". Check to see if it is .3mm that he was to mill off
Bill
12 thousands is .012 which is less than 1/64th of a inch.
 

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12 thousands is .012 which is less than 1/64th of a inch.
Yes it is but 3mm is .120 thousands and sorry didn't see the .3mm at the first post.
 

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SX has the TDC lock like the XC
 

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Trivial, but INSURE the arrow on the piston is facing toward the front or exhaust side of engine or the valves will hit the piston...he probably needs to do a squish clearance test if he is sure the piston is oriented correctly
Timing of course could do this also...

Too thin of a base gasket can do this...

Thats about all I know and I have done all three at one time or another...please don't tell anyone... :lol: :lol: :lol: ...funny when I had too thin of a base gasket it wouldn't hit the valves until about 3000 rpm

When I had the piston on backwards (Not all of them are marked so it wasn't all stupidity just ignorance on my part) it would hit the valves at idle, but would start and rrun fine
 

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Trivial, but INSURE the arrow on the piston is facing toward the front or exhaust side of engine or the valves will hit the piston...he probably needs to do a squish clearance test if he is sure the piston is oriented correctly
Timing of course could do this also...

Too thin of a base gasket can do this...

Thats about all I know and I have done all three at one time or another...please don't tell anyone... :lol: :lol: :lol: ...funny when I had too thin of a base gasket it wouldn't hit the valves until about 3000 rpm

When I had the piston on backwards (Not all of them are marked so it wasn't all stupidity just ignorance on my part) it would hit the valves at idle, but would start and rrun fine
No Base gasket on the RF4 motor Orings inserted in the case around the base of the cly. sleeve their is a mark on the top cam chain gear. rotate the crank 6 times to line up set TDC stop bolt and install cams.
Bill
 

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No Base gasket on the RF4 motor Orings inserted in the case around the base of the cly. sleeve their is a mark on the top cam chain gear. rotate the crank 6 times to line up set TDC stop bolt and install cams.
Bill
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You will have to degree in the cams and it should be fine.
 

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Discussion Starter · #12 ·
He milled it 30,000ths witch is 2 1/2 times bigger.
 

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