Valves & Pistons Contact

[icanfixall]

I found this really interesting information in my International Engine Service Manual. It states that when the heads are going back on and you start installing the rocker arms the motor must be turned past top dead center just about half the distance between that mark and the 12 oclock position. So if you looking at the front of the motor and its timed to the marks now turn the crank half way from that point to 12 oclock and the valves wont hit a piston when you tightening down the bolts. I never knew this. I'll be assembling my motor in a week or two so I'll try this and post back what I feel....

 

[h2odrx]

this would only be if you had it retimed? if you just pulled the heads and replaced the gaskets it should be ok?
thanks!
dwight

 

[subway]

it would be fine if you were just pulling the heads because the crank shaft would still be timed with the camshaft. i dont see how this would be a problem unless you some how rotated the the cam independant of the crank and tried re-assembly without lining it back up. most all newer engines that i know of are interferance engines like this.

always something to keep in mind though

 

[icanfixall]

Ok guys... Turning the crank turns the cam at half the rate of the crank. This movement of the crank sets all the pistons just below top of the strokes so no piston to valve contact will take place when your tightening up the rocker arm bolts. Nothing gets out of time or are you retimong anything. I hope this clears things up some.

 

[typ4]

You can get contact when just removing and replacing head gaskets because the lifters can relax and fill with oil, then when you tighten the rockers the lifters dont bleed off the extra oil and the valves can contact the piston. The manual method is good, if the heads are off just turn the crank till all are down a bit, good to go.
It is a good thing it takes a long time to get from rocker install to start up or we would have all kinds of bent stuff.

 

[Agnem]

Ah! That explains why the manual says to set the crank to such and such a position before servicing head gaskets. I've never done this, and never had a problem, but I always wondered why that was. I don't see the lifters changing any when your just disassembling and reassembling, but if introducing new lifters I can see where this may become critical.

 

[subway]

i could be wrong but i thought that the lifters would go down when assembling the engine because there is no oil pressure to to pump them up. i would think unless you assembled like superman that there would be no way for the lifters to overcome the valve spring pressure by themselves.

better safe than sorry though

 

[Agnem]

Maybe it could happen if you swapped used ones around? Dunno.

 

[typ4]

The lifters suck up a little bit of oil when you relieve the rocker tension,oil runs down the pushrod and in the lifter top hole, then the lifter is effectively taller when reassembled. Yes the valvespring will push it down but not near as fast as you can tighten the rocker bolts. oil doesnt compress remember

I had an 11.5 comp chev with domed pistons and dont ask how I know the valves will bend first.

 

[icanfixall]

Oh yeah... On this planet we can't compress fluids...... Thats why some blocks have windows in them. Ever see a top fuel motor that can "drink" 10 gallons of nitro and just a splash of methonel in 4.5 seconds loose the fire in one cylinder??? The piston (if it stays on the rod) pushes the fuel out the sides and down past the rings. Then things really start to leave their places in line.