PC high compression head piston sound like its hitting the head

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BMS420

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Jan 18, 2012
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Just a quick question, I believe my piston is hitting my PC head I hear a tapping sound when motor is running if I add another head gasket will I lose compression? I think I know the answer lol also it's seems this head is for the bigger engine studs I think mines is 6mm and I think the head uses 8mm if I drill out for the bigger studs would this stop the tapping?:-||
 
Venice Motor Bikes

Venice Motor Bikes

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Make sure the head is perfectly centered on the cylinder when you tighten the bolts.
If it's slightly off center, the piston might be able to touch the new head.
 
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BMS420

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Cool ... Going to give that a try I was thinking that too cause with the smaller studs the head sides around a lot before tighten down
 
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locutus_1

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Oct 31, 2010
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dont add another head gasket you will create a leak.. a solid head gasket 1 piece is the way to go if you are hitting the head then you need to change back to your stock setup or go to a shop that cnc and have them cut out alittle bit of room.. yes it will lower your compression...and once you pull off the head look closely at the piston make sure i t is ok

you dont want a piece flying off causing the piston to explode causing it to blow though the side and possibly into your leg .
 
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BMS420

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locutus_1 said:
dont add another head gasket you will create a leak.. a solid head gasket 1 piece is the way to go if you are hitting the head then you need to change back to your stock setup or go to a shop that cnc and have them cut out alittle bit of room.. yes it will lower your compression...and once you pull off the head look closely at the piston make sure i t is ok

you dont want a piece flying off causing the piston to explode causing it to blow though the side and possibly into your leg .
Click to expand...
Thanks.. I ended up finding a thicker head gasket but need a new bottom end cause the head bolts at the case are stripped and I don't really want ( or have a pully tool) to rebuild with a new case , but yea befor that I found a thicker gasket
 
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locutus_1

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BMS420 said:
Thanks.. I ended up finding a thicker head gasket but need a new bottom end cause the head bolts at the case are stripped and I don't really want ( or have a pully tool) to rebuild with a new case , but yea befor that I found a thicker gasket
Click to expand...
get the stock head bolts or heat treated bolts other wise the heating and cooling of the head will snap the bolts.. and retap the threads on the head with the right size tap.. and your welcome... a thicker gasket might do it but
you shoulndt need a thick gasket if its deisgned for that piston and stroke etc
 
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locutus_1

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moonerdizzle said:
if the case is stripped you could always drill out and put in some helicoils
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no no no not on a head..most likely they will work there way out... if its stripped just make the hole 1 size bigger and re tap it then use the appropriate bolt

never want to do fixes like that on a major component do them the rightway..

first determain if it has enought meat meaning steel around the hole so it wont punch though the wall of the cylinder if you go up one size.. and check your head to make sure it wont go into the compression part when you drill the hole bigger for the bolt..
 
moonerdizzle

moonerdizzle

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locutus_1 said:
no no no not on a head..most likely they will work there way out... if its stripped just make the hole 1 size bigger and re tap it then use the appropriate bolt

never want to do fixes like that on a major component do them the rightway..

first determain if it has enought meat meaning steel around the hole so it wont punch though the wall of the cylinder if you go up one size.. and check your head to make sure it wont go into the compression part when you drill the hole bigger for the bolt..
Click to expand...
i had to put one helicoil in my case.head stud wasnt fully threaded into the case and stripped out, put in a metric helicoil and havent had a problem since. worked out perfect. helicoils work fine for stripped out head studs, just pull the stud out, drill the hole out with the drill bit from the kit, tap it, and insert the helicoil with red locktite.

And what do you mean steel? there is almost no steel in these motors. the cases, jugs, and heads are all aluminum.
 
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BMS420

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moonerdizzle said:
if the case is stripped you could always drill out and put in some helicoils
Click to expand...
Thanks guys for all the advice... I'm in Hawaii and Ace nor Home Depot here carries helicoils or the like so I would have to order and waiting sucks, this is my second build first was with the skyhawk gt5 66cc and I blew the top end and rebuilt it but didn't clear out the case so I messed up two top ends before just buying the bgf 66cc with 6mm studs so now that I got the PC head I wanted the change out the 6mm for the 8mm that where in the skyhawk and I drilled and tap for the 8's but this aluminum is softer on the BGF engine than the skyhawk .. So instead of waiting on helicoils and the slow a$$ daily sort at the local post office on top of shipping time I rather get the skyhawk bottom end , cause I have the arrow cycles reedkit combo coming in tomorrow and that pretty much a skyhawk top end ported with reeds.. Lazy cause I have that one skyhawk bottom end and could order the the crank pully tool like what $3 and change plus shipping and clear or repair the skyhawk bottom end that I have but at this point I'm just going to spend the $74 plus shipping for a new skyhawk bottom end... Hate typing on a IPhone
Again thanks for the replies:-||
 
Salvor6

Salvor6

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Jan 30, 2013
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Just got my HC head from Pistonbikes. WOW! This thing is MASSIVE. I had to cut some of the fins to make it fit but this does not harm the head or its cooling properties.
 

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