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Ah, so that AEM sounds like a different cam gear than I saw on a video. They installed everything and it was still in the engine stand and they'd been spinning it for other things when someone noticed a clicking or something. They took the belt back off and discovered the cam gear bolts on the back were hitting the block or a bolt. I think they machined the bolt heads on the back of the gear for clearance, and I'm pretty sure it was the intake cam like yours.. Anyhow, that's a definite suspect and I guess the thrust movement of the new camshaft would also be curious to measure. I'm sure your shop knows this, but be very, very careful about torquing down the cam journals. Into aluminum, bolt torque doesn't "fetch up" like it would into steel. The proper torque feels like it's smearing into correct torque. I used a beam style where you can get to the right torque and hold the tool in place for a second. If the beam "unwinds" (the fastener turns), then you're not at the right torque. A click you can't "see" this..
 

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That dowel pin is to locate the gear on the cam, not to keep the gear from spinning. The bolt's clamping force between the gear and cam keeps the gear from spinning. If the pin broke, either the bolt was not tightened properly or the mating surfaces were not clean.
 

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That's true. But it broke because it was the only thing stopping it turning. Could be a bolt torque issue. Or something caused the cam to drag and exceed the design spec for drive torque. Best case scenario the bolt was loose and its an easy fix.
 

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Did you have the head decked? Decking the head is a good idea if its out of spec but the reality is that if the cylinder head surfaces is bent so is the camshaft side.

If the head bows up a little in the middle it will be straight when torqued down thats why they have the tightening sequence the way they do. If its to much then it has to be addressed. When you deck it you end up removing material from the sides and almost none from the middle. Think about what that means for the camshaft side. Camshafts binding after it gets good and hot is very real in that circumstance. The pin breaking is just a fail safe to keep the damage from spreading in a binding situation. If the camshaft side was off and it got decked it will be crooked by the same amount as the material removed off the head surface plus what it was off to begin with.... (If that makes sense)

Dont just check the camshaft for evenness front to back but also down the line. They deform naturally. Decking just addresses one issue of head deformity. Most machine shops wont straighten the top unless you tell them directly.

Sorry for rambling on a first post.
 

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I'd imagine the shop did the right thing there. I'm a hacker and even I knew to bolt the head down without the valves, and confirm it spins nicely without any "the head is now warping the cam bores" effect. So I'd think the shop would have that in its standard spec check. That is good information to know of course. Many a head has been ruined by the process done wrong. At this point it will truly be up to the shop to double check their work and then be honest about what they find if it was a bad camshaft fit they should have noticed. The bummer is the OP put on the timing gears and would therefore be responsible for any incompatibility. It's sure got me thinking of a dab of loctite on my dowel pins before I torque the gears down.

Either way, for one brief moment in time, the OP had the world's first and only VVT 7MGTE.

Sorry, OP - someone had to say that......
 

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When you have something loose in the head that somehow binds or blocks camshaft rotation (typically spitting a shim or a loose piece of hardware) 9 times out of 10 it'll spit the timing belt off the cam gear or break the camshaft.

When the cam bolt is improperly torqued or something else happens to allow the cam bolt to gradually loosen a little bit, it'll beat the shit out of the cam pin which was never designed to take that load, and it'll and break and shear off as seen here.

A lot of these BC 272's have ended up in a lot of 7M's at this point, I really don't think there was an issue with the camshaft unless you're seeing specific damage to corroborate or suggest a camshaft specific issue. This thread reads to me like some kind of install issue caused either by a bad cam gear bolt, a torque wrench that's out of spec, or something else that allowed the cam gear bolt to loosen up while the engine was running.


Did you have the head decked? Decking the head is a good idea if its out of spec but the reality is that if the cylinder head surfaces is bent so is the camshaft side.

If the head bows up a little in the middle it will be straight when torqued down thats why they have the tightening sequence the way they do. If its to much then it has to be addressed. When you deck it you end up removing material from the sides and almost none from the middle. Think about what that means for the camshaft side. Camshafts binding after it gets good and hot is very real in that circumstance. The pin breaking is just a fail safe to keep the damage from spreading in a binding situation. If the camshaft side was off and it got decked it will be crooked by the same amount as the material removed off the head surface plus what it was off to begin with.... (If that makes sense)

Dont just check the camshaft for evenness front to back but also down the line. They deform naturally. Decking just addresses one issue of head deformity. Most machine shops wont straighten the top unless you tell them directly.

Sorry for rambling on a first post.
The M nor the JZ engines depend on a head 'warp' that lines back up when it's torqued down. The only alignment/machine work issue I've ever seen in a JZ or 7M head came from a sloppy machine shop decking the cyl head at a cant, so the HG mating surface was canted just enough that ARP head studs didn't sit in the middle of the bolt bores for the cyl head. It was discovered on assembly, I'm pretty sure it would have ran albeit with misalgned coolant passages, stuff not fitting quite right in the engine bay, etc.

Line boring of the cams is usually only needed if a camshaft breaks or if you're matching cam caps from another head onto that cyl head.
 
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Discussion Starter · #28 ·
Machine shop of course said the head is garbage, and the intake cam. I sent him my back up head with it so that one is being inspected.. COD by their estimation was too much tension on the timing belt. I don't exactly agree with this as there wasn't an belt noise on start up, squeals, nothing of the sort. I would believe the improper torque or failed bolt on the pulley... BC said they think they have a single cam they can sell me.
I'll get the head back and take pictures of it. I will be sending it out to get a second opinion.
 

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Discussion Starter · #29 ·
This head was supposed to have been decked, 45 angle valve job, new stem seals, cams clocked, valves adjusted, added 6th cylinder coolant port, arp washer inserts with the studs. There is no reason, outside of error, that it should have had an issue.
 

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An over tensioned belt and under torqued cam bolt could have resulted in this kind of failure.
We're all just guessing though.

Either way something got screwed up on assembly.

Really unfortunate, hopefully you are able to resolve this.
 

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Discussion Starter · #31 ·
Hope so, machine shop said today both of my heads are no good. The BHG head is warped .016” which I saw coming, the head we have been discussing he said the first journal is fucked. So looking for a head. Will send this one out for 2nd opinion like stated before. Damn..
 

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I've never done it but supposedly you can straighten a head by heating it up in a press. That's if the aluminum still passes the hardness test.
 

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Z06 - where to you live? I've got a super talented cylinder head shop here and they do dozens a day, every day of the week and are not expensive. Spokane, WA is across the state line from me but I'm asking because someone else may get on here and say "Really, you're down the street, I have a..."

Also, I'd like to see that #1 journal in a photo. That's the bigger heavy one (versus the actual "first journal") with the factory deep groove on it, yes?
 

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Discussion Starter · #34 ·
I will send pics he’s shipping them back to me (my local parts shop) I’m in Illinois
 

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Discussion Starter · #36 ·
It is. I’m not having him do the work since they aren’t going to do anything. I’ve got another machine shop I’m going to try local. My heads should get back in town today.
 

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If you're in Illinois, you should be talking to Sound Performance to get this done.

Excessive timing belt tension will bend/break the tensioner pulley or the oil pump drive gear long before it'll cause a failure like this. I'm pretty solidly convinced that something led to improper torque or improper seating of the cam gear bolt and that allowed it to work itself loose.
 
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Discussion Starter · #39 ·

BC dropped me an intake cam in the mail today. Acquired a head from a member. Cam says Tuesday for arrival and the lot goes back to machine shop for a second opinion on the head in question and to do this second one up nice
 

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Which head/cam is pictured? I followed the link to the other photos. Only comment so far is the assembly guy sure didn't worry about excess sealant falling into your oiling system - that's crappy practice for starters...
 
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