Pistons hitting valves HELP!!
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Junior User
Joined: Nov 2011
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Pistons hitting valves HELP!!
1992 7.3 IDI
I am rebuilding my engine and the pistons (.020 over, newly bored/decked block) are striking the head with a new cam grind done by DeltaCams. So, checked the old cam that was running with this engine. I am turning the crank manually and only get a quarter turn before the pistons hit with the original cam. The timing is aligned and I am out of ideas.
I am rebuilding my engine and the pistons (.020 over, newly bored/decked block) are striking the head with a new cam grind done by DeltaCams. So, checked the old cam that was running with this engine. I am turning the crank manually and only get a quarter turn before the pistons hit with the original cam. The timing is aligned and I am out of ideas.
Logistics Pro
Joined: Jun 2012
Posts: 4,063
Likes: 2
From: Southeastern IL
I know I'm prolly gonna say something obvious but something's not adding up. Either they ground the cam WAY wrong or your timing chain is off. Start simple! Does ur timing chain have those dimples in it to tell ya its right on and are they nose to nose?
Posting Guru
Joined: Jan 2010
Posts: 1,665
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From: Terre Haute, IN
How much did they take off the block? One of the senior guys on OBN said the normal clearance between piston and head is 0.042". If they took more than that off you may have to find a thicker head gasket, or have the pistons shaved....
Posting Guru
Joined: Jan 2010
Posts: 1,665
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From: Terre Haute, IN
I don't want to make a blanket statement, but i think all diesels are interference design because of the long stroke needed for the high compression.
Fleet Owner
Joined: Jul 2006
Posts: 20,359
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From: Mi'kma'ki
i grabbed this a while ago.i think it was icanfixall who posted it originally.but it might be someone else.it was over a year probably so i can't recall exactly.almost sure it was from obn and from him.
anyway,in case it helps;
anyway,in case it helps;
Postmaster
Joined: Dec 2004
Posts: 2,941
Likes: 30
From: Maple Valley, WA
What is the cam grind number??
I was just talking to Ken from Delta today in person, and we were talking about how they index the cams in on the machine, and that being the case, Its pretty much impossible to have the cam ground that far off... Its gotta be an install/machining issue...
I was just talking to Ken from Delta today in person, and we were talking about how they index the cams in on the machine, and that being the case, Its pretty much impossible to have the cam ground that far off... Its gotta be an install/machining issue...
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Senior User
Joined: Jan 2013
Posts: 420
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From: Naples FL
i dont wanna sound like a *** but did u deck the block as well as heads if so good luck finding a copper gead gasket the right thickness ... or you did not do anything to the heads as in slap ebay valves in it did u ? if so they may be wrong .. if it was a cam grind on a already stock cam no way would it hit they take metal away right ?!?! someone x3 check me good luck
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Postmaster
Joined: Feb 2011
Posts: 3,560
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i'm sure they're interference engines. the piston is a flat top with only small dimples at the valves, and the head is nearly flat, unlike most gas motors with a fairly large bowl that the valves sit in. for it to not be interference would require insanely small valve opening.
i'm betting you'll need your pistons shaved by about as much as you took off the block
i'm betting you'll need your pistons shaved by about as much as you took off the block
Postmaster
Joined: Feb 2011
Posts: 3,560
Likes: 1
actually rocky, a cam grind on your existing cam is able to produce more lift by taking down the base circle of the cam while keeping the original height of the lobe. this would then be compensated for by longer pushrods or adjusting the rockers on engines that have adjustable rockers (not ours).
hope thats not the case but be sure to check your berring if the above is the case
Laughing Gas
Joined: Aug 2003
Posts: 919
Likes: 4
From: Newberg Oregon
These engines run close, if the head rebuilder used thick margin valves you are screwed. If they shaved the block and head it is worse, make darn sure your gear is all the way on the cam. if not it can change timing enough to hit, now are the lifters full of oil and need to bleed down? take this slow and double check everything, the valves are a common problem, the reliefs in the piston are not for valves its for flame travel, valves are outside the holes some.
Senior User
Joined: Jan 2013
Posts: 420
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From: Naples FL
These engines run close, if the head rebuilder used thick margin valves you are screwed. If they shaved the block and head it is worse, make darn sure your gear is all the way on the cam. if not it can change timing enough to hit, now are the lifters full of oil and need to bleed down? take this slow and double check everything, the valves are a common problem, the reliefs in the piston are not for valves its for flame travel, valves are outside the holes some.
Senior User
Joined: Feb 2012
Posts: 445
Likes: 6
From: western Oregon
There are no relief cuts in the IDI piston. The cut out is .085 deep and is a cumbustion swirl area I can't remember the name for it at this time. The engine has pistons that can be above deck almost .040 this makes decking the block and heads verry tricky to do both on the same engine without using .010 lower hight pistons made for decked blocks. I cut my pistons in a mill .030 to drop compression and to give some extra room for my J2 cam. When you cut .030 off the pistons they drop about 22 grams of weight. I cut 8 grams more off when I balanced the set. then you should balance the crank and rod assembly to the lighter pistons. My thoughts on your fit problem is to check the piston hight above deck and see what you have. I think the gasket smashes down to .085 or so when torqed so you need to do some checking and do the math and see where your at. recheck your timing marks if everything is correct the only thing it can be is your shop cut to much off when they decked your parts. Dam I type slow....