240Z, 260Z, 280Z Performance / Technical Discussions related to performance motor enhancements, upgrades.

280z timing jump.. uh oh.

Old 06-22-2015, 06:24 AM
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280z timing jump.. uh oh.

Last summer i jumped the timing in a zmotor.. its a n42 head and block.
I then pulled it and put it on the garage floor.. now this summer i have all the replacement parts. ( new sliders, tentioner, gaskets, studs, sprockets, and chain)

motor ran awesome prior to me pushing it too hard... it has flat top pistons.. big cam.. lightwieght flywheel, slightly shaved head.. ported oil gallies ( more oil flow) and smoothened out rocker arms.. very nice motor and i wish to repair it.
only has 5000miles on it.

Previous owner is long gone and no longer a source to talk to :/
After searching around older threads and pictures im still having a hard time finding out how to do it from scratch..

Motor is all apart already.. old timing components already removed.
Have all new parts on bench awaiting install..

Motor is supposedly at tcd on #1. but crank has its keyways appearing to be in the 2 oclockish position.. same with cam... i cant turn either one individually either way to get it all lined up at 12. When i turn by hand it doesnt allow me to move it very far before hitting a valve.

I hope i didnt already smack a valve.. should i just go ahead and pull the head to be sure of this?.. After floating the chain at high rpm the motor just revved down and died.. then could still turn over but not fire up again.

So here I am today with a pile of pieces and not sure the best way to inspect/ align/ and fix.

Any input/advice/ help.. is greatly appreciated. Thankyou




I revved the motor to the moon and it floated the chain about 3 or 4 teeth over.
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Old 06-22-2015, 06:57 AM
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My .02.
The only way for sure you would know if you didn't smack a valve would be to open it up, OR maybe...run a cam into each cyl from spark holes and see if you can see any scarring on the top of piston.
Reason you could turn it by hand and now you can't is simple, the chain was on turning the cam and the crank at the same time, therefore moving piston/valve out of each others space, but now that the chain is off, they will be hitting each other.

There is no "supposedly" with timing, either it is or not, you can't be guessing. You need to know for sure. There is a lot of write-ups and images about setting the timing and installing new timing hardware.



Good luck.
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Old 06-24-2015, 04:56 AM
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both good ideas at this point probably..thankyou

one more thing i forgot to mention was after i did this last summer.. i tried to cheat at this and take the top cam sproket off because it was paint marked on chain and sprocket on 3 little points.. all within 3 inches of each other.. ( wish i could show picture but i removed all this already) sorry.. but when i initially saw this it jumped from the marks about 3 or 4 teeth.. so like i said i removed
sprocket carefully and kept tention on chain with a dowel into the cam for leverage.. then rotated things back so it was lined up with the marks again.. popped sprocket back on and tried to start and it just slammed to a stop..
then i pulled motor out of car and put it on the floor and threw a stock motor into it and sold car to a friend..

now i just want to repair it and put it in my 240z. but after doing what ive done.. i should probably just pull the head and check/ redo everything.

This is the 1st motor i get really apart and into.. it appears to have a metal head gasket.. are those stock?.. either way I should probly measure the thickness to make sure i dont get a thinner one than I have.
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Old 06-24-2015, 06:53 AM
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Originally Posted by 7d82adz View Post
so like i said i removed
sprocket carefully and kept tention on chain with a dowel into the cam for leverage..
That's not how you keep tension on the chain... you use a 1" wood block and shove it in between the chain as it goes down into the guides. If you didn't do that, then the hydraulic tensioner below popped out and then you have major problems.

See: https://www.zdriver.com/forums/240z-...on-pics-19939/

Originally Posted by 7d82adz View Post
it appears to have a metal head gasket.. are those stock
MLS head gaskets have rivet tabs that stick out the side.

Attached Thumbnails 280z timing jump.. uh oh.-l28e-mls-hg.jpg  
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Old 06-24-2015, 02:03 PM
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Originally Posted by 7d82adz View Post
both good ideas at this point probably..thankyou

one more thing i forgot to mention was after i did this last summer.. i tried to cheat at this and take the top cam sproket off because it was paint marked on chain and sprocket on 3 little points.. all within 3 inches of each other.. ( wish i could show picture but i removed all this already) sorry.. but when i initially saw this it jumped from the marks about 3 or 4 teeth.. so like i said i removed
sprocket carefully and kept tention on chain with a dowel into the cam for leverage.. then rotated things back so it was lined up with the marks again.. popped sprocket back on and tried to start and it just slammed to a stop..
then i pulled motor out of car and put it on the floor and threw a stock motor into it and sold car to a friend..

now i just want to repair it and put it in my 240z. but after doing what ive done.. i should probably just pull the head and check/ redo everything.

This is the 1st motor i get really apart and into.. it appears to have a metal head gasket.. are those stock?.. either way I should probly measure the thickness to make sure i dont get a thinner one than I have.
Ay, I would pull the head, pull the timing cover off as well, check everything.
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