piston to valve clearance?

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joshua dewitt

joshua dewitt

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ok, im confused building a 1st time 318 performance build. been a chevy guy in past, i crossed teh line, hehehehe...
ok i have a 73 virgin 318 block, just a standard polish crank, new eagle rods with arp bolts, new press fit 87-91 318 9:1 flat top pistions( all flat, no reliefes) seam to be all like that, afer assemble, close to a near zero deck ... just under, .0190"
now i found som #302 casting heads allready rebuild, set them on with ath the old head gasket @ .035" all ready comrpresed... and some modeling clay on pistion... using the mopar performance 340 resto cam, and matching lifter, went to check clerance, using an old 318 original lifter, i tackwelded solid for moc up, and won"t roate, exhaust valve hits,... using a mechanical lifter,( has a deeper relief in it form parts store,) and valves will barely open? using the new lifters, ( mp 340 matching) with comp cams (stock length) push rods, will spin, but very close and possible draging on top of pistion, don't even have oi pressure holding lifter up yet. has anyone heard of tihs beign a problem? from what i read, the facotry 87-91 pistions are the same as 73 just differant compreiion height, 8.0 to a 9.1... and thease are the heads that are suposed to mate for those years, the rocerks say "91 on them? what gives, any ideas, do i have to get differant pistions with vavle reliefs, or am i missing something here?
 
I tried something close to your setup and had the same problem with those flat top pistons they are usually about .100 down the hole at tdc but mine were .030. I pulled them and had flycut the valve reliefs cut .120 on exhaust, and .100 for the intakes. I was using a .454 lift cam with only 272 degs. duration. with a 108 lc.
 
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The push rod is pushed into the lifter.....well it vary but .020-.060" if you welded up the lifter to make it solid and then used the stock push rod, you are opening the valve .020 to .060" more then the cam's lift.

Example, you have a head that pushes the push rod into the lifter .020 and you have a .474 lift cam. the valve will open up .494" not .474. If the push rod sit in the lifter .060" well, now you have the valve lifting .534 lift.

You need an adj push rod OR you need to sink the lifter plunger the same length as the rest of the lifter are..........then weld it.
 
ok. i may have found my problem, when at top dead center #1 pistion up, the cam lobe for the exhaust is up, causing the vavle to hit the pistion? now if memory serves ne correctly, when i set to tdc to remove the chain to do a cam swap the dots were both in the up postion? and it ran fine, well for a wore out engine? i now have a new cam and all new parts( morot) but reused the same crank. have anyone ran into the crank gear wouldrif key 180 degress off? been looking on internet, i'm not the only one who ran into this i guess? any thoughts?
 
i'm now starting to think this is how i took it apart and i was dumb founded then? i/m sure of it. when crank gear at 12(dot) where is the keyway pointing? im going to go check my mopar bibles....
 
Well, the piston will traverse TDC twice during the complete cycle; once with both valves closed, once with exhaust valve on it's way closed and the intake opening...
 
ok just checked to old chain( old double roller styler) my new comp cams chain set the cam gears mate the same, the crank gear the dot is totally in a differant spot, i have a square and a triangle and in the middle the (o) whick is straaight up. that is waht i need and want. now i compared where the woadruf key is and when dots poting at each other 6/12... the key way is at 5 o'clock, on my orignial is 2o'clock, i think i have a bad timing set crank gear what ya guys think?
 
Since the crank turns 2 to one, your dots on the crank/cam gear will be dot to dot then when you turn the crank one complete turn they will both be at 12 o clock.
 
joshua dewitt said:
ok just checked to old chain( old double roller styler) my new comp cams chain set the cam gears mate the same, the crank gear the dot is totally in a differant spot, i have a square and a triangle and in the middle the (o) whick is straaight up. that is waht i need and want. now i compared where the woadruf key is and when dots poting at each other 6/12... the key way is at 5 o'clock, on my orignial is 2o'clock, i think i have a bad timing set crank gear what ya guys think?
Click to expand...

Your crank gear has the three positions so you can install 0 degress or 4 advanced or 4 retarded. But you should really use a degree wheel to know exactly where your installing the cam at.
 
when i set to tdc to remove the chain to do a cam swap the dots were both in the up postion?
Click to expand...

I keep seeing this--am I the only person in the world who installs cams using the dot to dot method? Crank dot up, cam dot down-directly opposing each other?
 
no kidding, but did you see what i wrote, the crank gear is stamped wrong, or it is though i have the cam installed wrong, and for obvious reasons, comp cams either miss package, or stamped wrong. well back to the store, going to buy a ma mopar performeance one, that should work , i doubt comp will do anything...
 
Josh, could you post some pictures?...worth a thousand words and such, ya know...
 
txstang84 said:
I keep seeing this--am I the only person in the world who installs cams using the dot to dot method? Crank dot up, cam dot down-directly opposing each other?
Click to expand...

Installing dot to dot is the easiest way to make sure you they are lined up. But when you do this , you are actually on the number 6 fire position. If you rotate the crank one turn you are now at 12 and 12 o clock as far as the dots are concerned and you are now on the number one firing position.
 
Well, yeah, I'm aware of this, but it sure as hell makes things easier...I've assembled no less than 30 pushrod engines this way and it's never let me down.
 
Your method of using a solid lifter or a welded up hyd lifter will not work for checking PTV clearance unless you have an adjustable pushrod or rocker to set the lash to zero. As someone mentioned, you are probably holding the valve open. That amount +cam lift = piston to valve contact.
 
txstang84 said:
I keep seeing this--am I the only person in the world who installs cams using the dot to dot method? Crank dot up, cam dot down-directly opposing each other?
Click to expand...

nope, that's the way I was taught, that's the way in the service manual and that's the way we did it. when I was younger I was allways 180 off firing. lol now I get it right. lol
 
ok. i did find the problem.... it is the wrong crank gear given to me from comp cams confrimed with stamping numbers, i will be calling them tomarrow. and yes i will post a pic of the orignial and the new 3 way when i get it off. i didn't believe it myself. i have beenb build all these moderon ovh cam motors for so long and building tranmissins i for got to check the basics before i installed them. as the damn cranks gears and wodrift keys are worng... makes every thing of about a 90 degree turn of the crank to cam. making pistions hit valves. guess thats what happens when you don't think as you build, ....pics up soon.
 
txstang84 said:
I keep seeing this--am I the only person in the world who installs cams using the dot to dot method? Crank dot up, cam dot down-directly opposing each other?
Click to expand...

Technically, you are doing it right "per the book".

Either way will work, if you put both dots for the gears at 12 o'clock, they will also work out fine, just on the power stroke vs intake, but will be "correct" if you rotate the crank 360°.

There's two ways to skin this cat. Either one will work....


I find it easier when they are closer together myself also.
 
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