Pistons hitting valves HELP!!
Senior User
Joined: Feb 2012
Posts: 445
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From: western Oregon
If youn have a extra lifter to dissasemble you could find the stroke of the lifters hydrolic assembly then calculate the shim needed to get you back to the range needed for correct opperation. OR It is possible to order custom length push rods from speedway or sumit or jegs you just need to know the size you need.
Lead Driver
Joined: Sep 2005
Posts: 9,399
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From: Norco,CA
Custom puch Rods, but you still have to measure valve lift etc.. Should of done all that first. Piston height also. He must of cut off alot or never measured the height in the first place for this to happen.
Postmaster
Joined: Feb 2011
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i'm working with what i believe to be a totally stock camshaft and valve train. the PO had the engine rebuilt before i got it, but he appears to have done a totally stock rebuild, and neglected necessary machine work on the deck, which is why it failed in 90k miles, putting me where i am today.
for a test, i tossed some flat washers under the rocker arms, measuring about 0.060 or so because thats what was handy, and with those in place i have no slack in the pushrods, and i have enough clearance to rotate the engine freely. i plan to now go through with feeler gages to see how much clearance i have between valve and piston with those in place, and that should get me on the right track.
how much clearance do i need between valve and piston as a minimum tolarance when rotating? i know things expand as they warm up, and i would sure hate to have them too close where they hit when hot.
for a test, i tossed some flat washers under the rocker arms, measuring about 0.060 or so because thats what was handy, and with those in place i have no slack in the pushrods, and i have enough clearance to rotate the engine freely. i plan to now go through with feeler gages to see how much clearance i have between valve and piston with those in place, and that should get me on the right track.
how much clearance do i need between valve and piston as a minimum tolarance when rotating? i know things expand as they warm up, and i would sure hate to have them too close where they hit when hot.
Senior User
Joined: Feb 2012
Posts: 445
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From: western Oregon
Well in my chevy engines I run .090 as minimum valve clearance. But thats turning 7800 rpm. I don't know what the IDI needs. I think the closest valve is exhaust valve closing as the piston is coming up at it nearing the end of the exhaust stroke. the valves are set into the head about .065 or so. Have you bolted the heads on yet... you can reasemble them snug and put some puddy on the pistons and roll it over then take it apart and check the clearance with a caliper then do some figurin and then adjust as needed.....
Postmaster
Joined: Feb 2011
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i've got the heads all torqued down already, but if they have to come off, i guess it is what it is. if thats the case, i might try to find some thicker head gaskets and solve the problem that way, so far i've just been loosening different rockers and checking out clearances...
its looking like my only options are:
shorter pushrods (not listed from any manufacturer)
thicker head gasket (not listed anywhere online)
shave the tops off the pistons (i really don't want to tear it all apart again)
shim the rockers up like i tried - this definitely seems to be the most convenient method, and i can't think of any reason it wouldn't work. if it hits the valve cover, i can double up the gasket on that to make up for it.
i've never heard of it being done, but do you see any reason why this wouldn't work?
its looking like my only options are:
shorter pushrods (not listed from any manufacturer)
thicker head gasket (not listed anywhere online)
shave the tops off the pistons (i really don't want to tear it all apart again)
shim the rockers up like i tried - this definitely seems to be the most convenient method, and i can't think of any reason it wouldn't work. if it hits the valve cover, i can double up the gasket on that to make up for it.
i've never heard of it being done, but do you see any reason why this wouldn't work?
Postmaster
Joined: Feb 2011
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quick update - i found a pair of washers 0.040 thick and tried those under the rockers, then started stacking feeler gages between the valve tip and the rocker arm, found that a stack measuring 0.095 would clear on either valve, while a stack measuring 0.115 would clear the exhaust but not the intake.
so its looking like a box of washers measuring 0.040 thick will be the ticket for me. does that sound reasonable?
so its looking like a box of washers measuring 0.040 thick will be the ticket for me. does that sound reasonable?
Senior User
Joined: Feb 2012
Posts: 445
Likes: 6
From: western Oregon
Well that looks pretty good. .040 washers looks like the ticket. Were the lifters pumped up on this test?..If the lifters are not pumped up the distance might be less. I think you should check them all...I know its alot of work, but having some confidence in the clearance will go a long way to making you feel better. Good job sticking it out untill you found the problem and way to solve it.
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Postmaster
Joined: Feb 2011
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well typefour, thanks for the insight there - you've got a good point about lift being the same, i'll have to study it a bit more and see whats up. that means that even if i could find shorter pushrods, they wouldn't be the ticket either.
if i didn't mention it earlier, i had to have both the heads and the block resurfaced, a combined amount of .035 or 040, so thats what brought me to this issue.
if i didn't mention it earlier, i had to have both the heads and the block resurfaced, a combined amount of .035 or 040, so thats what brought me to this issue.
Postmaster
Joined: Oct 2008
Posts: 3,026
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From: Renton, WA
From other thread https://www.ford-trucks.com/forums/1...l#post12817399
I think this is a likely coulprit very worth exploring if you haven't already. Depending on what you have been doing there is a good chance the lifters are pumped all the way up or "stuck" up. Diagnosing this can be a real pain in your situation. When the rockers are tightened down normally if the lifters are pumped up the valve will both hit the piston and not close all the way preventing seal and compression.
ok, i've done a little more playing around on my piston-valve contact issue here, and i found that adding a washer of 0.040 under the rocker arm gives me enough clearance to rotate the engine with a stack of feeler gages between the rocker arm and the valve tip. the biggest i've tried so far was 0.095 of feeler gages and no contact while rotating the engine. i tried 0.115 and it cleared on the exhaust but touched on the intake. so it looks like i just need to pick up some more washers at 0.040 thick to shim my rockers up, and i'll be golden. any thoughts on this plan?
my only other options would be thicker head gaskets or shorter pushrods, neither of which seem to be available from any source i can contact after closing time on a friday night.
my only other options would be thicker head gaskets or shorter pushrods, neither of which seem to be available from any source i can contact after closing time on a friday night.
Wait this doesn't make any sense.
.040 under the rocker will loosen the clearences likely to the point that the lifters are all the way up. But then .095 between the valve and the rocker will push the valve down more making any clearance problems worse. I don't know the rocker ratio but they look like big block rockers which I think are 1.7 so .040 times 1.7 = .068 So by putting in the .040 shim and then adding .095 your actually adding .027 of "lift" to the valve.
This of course is all negated by the hydraulic lifters pumping up and removing all the clearance created by the shim.
.040 under the rocker will loosen the clearences likely to the point that the lifters are all the way up. But then .095 between the valve and the rocker will push the valve down more making any clearance problems worse. I don't know the rocker ratio but they look like big block rockers which I think are 1.7 so .040 times 1.7 = .068 So by putting in the .040 shim and then adding .095 your actually adding .027 of "lift" to the valve.
This of course is all negated by the hydraulic lifters pumping up and removing all the clearance created by the shim.
I think this is a likely coulprit very worth exploring if you haven't already. Depending on what you have been doing there is a good chance the lifters are pumped all the way up or "stuck" up. Diagnosing this can be a real pain in your situation. When the rockers are tightened down normally if the lifters are pumped up the valve will both hit the piston and not close all the way preventing seal and compression.
Postmaster
Joined: Feb 2011
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i found the problem guys - it was so obvious i should have seen it from the start. a number of lifters remained pumped up to their max the whole time, and seem unable to leak down. as a result, screwing the rockers down opened nearly all the valves, quite a bit.
so i repeated my earlier test by having all the rockers screwed down only to the point that i took out all the slack when the cam was on the base circle, and no more. a few of them compressed the lifter at this point, the others won't compress for anything. i repeated the test with an 095 feeler gage stack between valve and rocker, and this time i was able to turn it over on all of them, though some had a feeling of just barely touching each other.
so it sounds like new lifters will be the solution to my problem here.
so i repeated my earlier test by having all the rockers screwed down only to the point that i took out all the slack when the cam was on the base circle, and no more. a few of them compressed the lifter at this point, the others won't compress for anything. i repeated the test with an 095 feeler gage stack between valve and rocker, and this time i was able to turn it over on all of them, though some had a feeling of just barely touching each other.
so it sounds like new lifters will be the solution to my problem here.
Postmaster
Joined: Oct 2008
Posts: 3,026
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From: Renton, WA
First better, well they are already broken in to the cam, the cam and lifters break each other in, new lifters will have to do so again adding wear to your cam. Second they can be fixed, EVERY stuck lifter I have seen was a simple fix. Hydraulic lifters are just a piston with a check valve. That piston don't really move much though and the area of the stroke it doesn't move in gets gummed up with oil after decades of not being apart and allowed to go it's full stroke. They are easy to take apart, and just clean out that oil ring that is making them stick. Bodda bing bodda boom, fixed already broke in lifters for free.
Postmaster
Joined: Feb 2011
Posts: 3,560
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when i was new to wrenching, i cleaned up the lifters for an old 300-6, and viewed it as a cheap cost-cutting move, not as a really good option. so i'm aware of the simplicity, but was never aware of any real benefits to freshening up my old ones. thanks for the insight.
