Moparts
Cam timing and piston to valve
Posted By: sixty9bee
Cam timing and piston to valve - 01/17/09 11:50 PM
How much effect does cam timing effect piston to valve clearence?
subject engine is:
0 deck ross flattop 4.15 stroke 400
277 at 0.050 roller cam 700 lift
110 centerline installed at 110
edelbrock heads
Posted By: sixty9bee
Re: Cam timing and piston to valve - 01/17/09 11:54 PM
exhaust valve with no head gasket and 0 lash has contact with piston.
What suggestions to get the minimum clearance? quench is already set for .039 gasket?
Posted By: SCATPACK 1
Re: Cam timing and piston to valve - 01/18/09 12:05 AM
You could advance the cam some to get clearance. But if you are hitting, I would flycut valve relief notches into the pistons. I do not feel safe with less than .100 thou on the exhaust to piston.
I know it is more time consuming but do it any way and never have to worry about it.
Posted By: MR_P_BODY
Re: Cam timing and piston to valve - 01/18/09 12:05 AM
Whats the intake at. Advance it 4* and check it again.
I prefer to check it with the head gasket but thats
me. Use a pushrod length checker with 0 lash then
you can figure your lash in
Posted By: 440Jim
Re: Cam timing and piston to valve - 01/18/09 12:10 AM
Double check when you change the cam installed position. But as I recall, advancing the cam (going from an intake lobe installed position of 110 ATC to 106 ATC) will reduce intake piston to valve clearance, but increase the exhaust P2V clearance. If you are running 1.5 ratio rockers, it should be around 0.023" change. But the lobe profile can be different than what I am used to.
Let us know what numbers you measure.
I check this when I "map" a cam. And I see around 0.015" lobe lift change with 4 degree advance, measured atg +/- 8 degrees of TDC (that is where min piston to valve usually occurs).
Posted By: Bigbeep
Re: Cam timing and piston to valve - 01/18/09 12:21 AM
Good stuff here. I am in the process of chosing a new cam and will be doing this soon, I hope. Beep
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Posted By: tjmarcus1
Re: Cam timing and piston to valve - 01/18/09 01:02 AM
if he has contact with 0 lash and no headgasket, he has problems! the question is how much interference is there? also are you sure the cam is in at 110? if you factor .040 for gasket,.020 lash that's still only .060 minus the exact amount of interference. advancing to 106 might help, but not fix the prob.
Posted By: lewtot184
Re: Cam timing and piston to valve - 01/18/09 02:24 AM
going from a 110 installed centerline to 106 will probably only net .015" additional clearance. recheck installed centerline and true rocker ratio. if the centerline is correctly installed and the rocker ratio isn't way off then the pistons will need work.
Posted By: Anonymous
Re: Cam timing and piston to valve - 01/18/09 03:06 AM
before you go any further, check your intake valve clearance. if you have more clearance there you might be able to advance the cam and get enough for both. if not, you'll be flycustting pistons. most shelf ross pistons will not handle .700 lift safely.
Posted By: sixty9bee
Re: Cam timing and piston to valve - 01/18/09 03:28 AM
the rocker ratio is 1.5 the lash was at 0 and the interference was minimal, as a matter of fact was not noticable until a dial indicator was used to check exact clearance. the intake was checked and has more than enough room through entire range. we could have 60-80 thou removed from the intake clearance and still be around 90 through the cycle.
Posted By: tjmarcus1
Re: Cam timing and piston to valve - 01/18/09 03:47 AM
Quote:
the rocker ratio is 1.5 the lash was at 0 and the interference was minimal, as a matter of fact was not noticable until a dial indicator was used to check exact clearance. the intake was checked and has more than enough room through entire range. we could have 60-80 thou removed from the intake clearance and still be around 90 through the cycle.
with that much int. clearance, are you sure the cam is in right?
Posted By: MR_P_BODY
Re: Cam timing and piston to valve - 01/18/09 04:00 AM
Quote:
Quote:
the rocker ratio is 1.5 the lash was at 0 and the interference was minimal, as a matter of fact was not noticable until a dial indicator was used to check exact clearance. the intake was checked and has more than enough room through entire range. we could have 60-80 thou removed from the intake clearance and still be around 90 through the cycle.
with that much int. clearance, are you sure the cam is in right?
The cam does sound like its installed retarted more
than straight up
Posted By: Sport440
Re: Cam timing and piston to valve - 01/18/09 04:03 AM
Quote:
How much effect does cam timing effect piston to valve clearence?
On the intake side a 1* at the crank is equal to around .003 to .004 lift at the lobe times rocker ratio.
Now if the exhaust lobe profile is similer you should see the same. It may be less since its Landing the valve.
But, requardless, your probably looking at around a extra .020 exhaust P/V clearence, with a 4* advance.
mike 
Posted By: sixty9bee
Re: Cam timing and piston to valve - 01/18/09 04:14 AM
I know, it sounds like its in retarded. that was my first thought. checked and started over checked again. the valve relief is deeper on intake side. the only question on install is the cam is ground on 110 but my understanding is comp puts 4 degrees advance into the grind. if that is correct, it should probably not be installed at 110 right? by the way thanks for all the replies
Posted By: MR_P_BODY
Re: Cam timing and piston to valve - 01/18/09 04:28 AM
Quote:
I know, it sounds like its in retarded. that was my first thought. checked and started over checked again. the valve relief is deeper on intake side. the only question on install is the cam is ground on 110 but my understanding is comp puts 4 degrees advance into the grind. if that is correct, it should probably not be installed at 110 right? by the way thanks for all the replies
Yes they grind in advance but you still start at 110
for 0 then advance it from there if you want advance
Posted By: Sport440
Re: Cam timing and piston to valve - 01/18/09 05:43 AM
Quote:
Quote:
I know, it sounds like its in retarded. that was my first thought. checked and started over checked again. the valve relief is deeper on intake side. the only question on install is the cam is ground on 110 but my understanding is comp puts 4 degrees advance into the grind. if that is correct, it should probably not be installed at 110 right? by the way thanks for all the replies
Yes they grind in advance but you still start at 110
for 0 then advance it from there if you want advance
Where your cam is installed now at a 110* ICL with a 110* LS you are neither advanced or retarded. Your at 0* Even if the cam had 4* advance ground into it.
mike
Posted By: 440Jim
Re: Cam timing and piston to valve - 01/18/09 04:26 PM
The best solution is the machine the exhaust valve reliefs in the pistons. But with a 110 LSA cam, I would not be afraid to install it with the intake lobe centerline at 104 ATC if needed, and you are willing to accept the trade offs.
Posted By: Dodgem
Re: Cam timing and piston to valve - 01/18/09 04:54 PM
If comp cams says 106 on a 110 lobe center cam they install the dowel pin to try and have straight up be at 106 everything being equal. but the crank keyway , gear set and drilling the dowel in the pin is not an exact science With the exhaust being that
Posted By: Dodgem
Re: Cam timing and piston to valve - 01/18/09 05:01 PM
With the exhaust being that close and the intake that loose I'd say something is way out of whack and that cam is severly retarded? The intake valve is usually the issue. Check and re check your marks rolling over but at this point I would suggest a true cam degree job
Just my thoughts have degreed lots and lots of cams
Lost some in my copy and past?? LOL???
Posted By: sixty9bee
Re: Cam timing and piston to valve - 01/18/09 05:08 PM
probably should have also stated its split duration 277 intake 285 exhaust. degree'ed several but not an expert by any means. does the procedure change any for split duration? the only explanation i can come up with is that the valve pockets are deeper on the intake side (according to the paperwork on the pistons) and the longer exhaust duration is the culprit. is this logical or am i grasping straws? the pistons have no additional fly cutting only the ross factory reliefs
Posted By: Anonymous
Re: Cam timing and piston to valve - 01/18/09 05:29 PM
I haven't seen a Ross piston for a wedge that will handle .700 without fly cutting pistons...Better off doing it now instead of fixing a dropped/bent valve..
Posted By: Dodgem
Re: Cam timing and piston to valve - 01/18/09 05:31 PM
My roller on my old 542 was 274 and 282 and they were fairly even in clearance with the exhaust having more of coarse It is common now but the intake centerine procedure is the same. I degree intake and exhaust often. And we have had brain fart days where we started with the exhaust lifter and we scratching our heads?? then the oh S$$$ we're in the wrong lifter. If your using seat to seat lobe lift .033 is eqaul to .050 at the valve seat so I do
that and .100 before and after Max lift to be sure.
If your shooting for 106 ATDC intake the exhaust lobe max lift will be at 114 ABDC
Posted By: sixty9bee
Re: Cam timing and piston to valve - 01/18/09 05:41 PM
Sounds like we are all pretty sure fly cutting is the answer. now how much can safely be cut or how much is a minimum thickness left after cutting? has anyone cut with shortblock assembled? i know isky and others make a tool for this but is it safe and accurate? what about the balancing? thanks again for the replies