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Ptero

Matching cam & crank timing

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Forgive me... dumb questions coming up.  (I've searched but haven't found the exact answer I'm looking for)

 

So it turns out I like learning things the hard way.

 

I did a dumb thing and pulled apart an l28et about 2 years ago and didn't mark anything in respect to timing.  The goal was to do a refresh /w new gaskets & timing chain as I found that one of the timing guides had snapped in two from what I can only imagine is chain stretch.  The block is currently at TDC and the cylinder head has been removed.  For the purpose of my question, lets say the head is not at what would have been matching TDC of the block.  After doing some searching people seem to mostly say the cam lobes on #1 should have the rabbit ears.  That's pretty vague and can be interpreted differently by each person by just visually looking at it.  Is there something more precise than that?  Can I adjust the head independently now that it's not attached to the block to make sure the cam is in the correct position before attaching it back to the block?  Do you get the best bunny ears you can, install the head /w cam sprocket lined up /w #1 on the sprocket and it'll be pretty close with a little movement to align the teeth of the sprockets to the timing chain?

 

Probably over thinking it, but this is all a learning experience for me.  

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There are factory Service Manuals on line.  Can timing has to be EXACT. There are special markings on the Chain, Cam gear, Crank gear and Thrust plate that all have to be aligned correctly.  Eyeballing things with " Bunny Ears " is going to end in tears. 

 

Here is a .PDF of an L28 Engine section. NA and Turbo are all the same.

 

Read it. Then read it again and follow the procedures.

 

EM.pdf 

 

 

Edited by Chickenman

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Best way to make sure you get things correct now, is to pull the front Timing cover.

 

Next time make marks on everything with a Grease Paint Pen. I use two different colors of Marker and mark more than one area. In case the paint gets rubbed off accidentally. 

Edited by Chickenman

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On 9/21/2018 at 9:14 PM, Chickenman said:

Best way to make sure you get things correct now, is to pull the front Timing cover.

 

Next time make marks on everything with a Grease Paint Pen. I use two different colors of Marker and mark more than one area. In case the paint gets rubbed off accidentally. 

 

After looking at it, I think it's making more sense now.

 

Timing cover isn't on as the head and block are separated.  Timing chain is obviously not on due to that as well.

 

So if I'm looking at this right...  Keep in mind the cylinder head is not connected to the block.  Cylinder head can be timed by having the #1 mark sprocket notch line up with the oblong groove.  I believe the FSM even says the groove would be slightly to the right of the oblong marking.  Lobes at this point should be the "rabbit ears".  Making sure the block is at TDC on #1 cylinder is pretty easy because the head isn't on.  Now I can mate the head /w the block knowing they're both at the correct positions to put on the timing chain.

 

Am I on the right path here?

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On 9/23/2018 at 5:04 PM, Ptero said:

Looks like this is all covered in chapter 2 of the infamous "How to Rebuild your Datsun Engine".

 

It would appear my comment above is correct.

Yes, you're on the right track.  Once you have this orientation between block and head the chain has to have a specific number of links between the marked tooth (marked with a dot) on the crank sprocket and the similarly marked tooth on the cam sprocket.  This is what the two bright links on the chain are there for.  

 

Side note:  This method only gets you "close enough" to run reasonably well.  It doesn't guarantee exact cam timing.  To do that, refer to this thread.  It's a bit more involved process and requires a dial indicator and a degree wheel, but if you've got the engine out already this a great time to learn the proper way to install and time a cam.

 

Edited by TimZ

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9 hours ago, TimZ said:

Yes, you're on the right track.  Once you have this orientation between block and head the chain has to have a specific number of links between the marked tooth (marked with a dot) on the crank sprocket and the similarly marked tooth on the cam sprocket.  This is what the two bright links on the chain are there for.  

 

Side note:  This method only gets you "close enough" to run reasonably well.  It doesn't guarantee exact cam timing.  To do that, refer to this thread.  It's a bit more involved process and requires a dial indicator and a degree wheel, but if you've got the engine out already this a great time to learn the proper way in install and time a cam.

 

 

I saw that thread last night.  It was late.  There were big words.  I'll read through that thread once I've got my caffeine.  At this point there's a certain amount of "while I'm here" thought process and I'm trying to curb unnecessary steps.  This looks to be something worth doing.

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On 9/26/2018 at 8:19 AM, Ptero said:

 

I saw that thread last night.  It was late.  There were big words.  I'll read through that thread once I've got my caffeine.  At this point there's a certain amount of "while I'm here" thought process and I'm trying to curb unnecessary steps.  This looks to be something worth doing.

 

 

 Not sure if degreeing the cam makes much sense without a degree wheel? But maybe it does. I did check my timing and it was "kinda" ok. I was 2-3 degrees of on every event, I think that was due to inaccuracy in my readings. 

It's a fun exercise to at least check the timing of your cam, gives you a little better understanding of everything. But I wouldn't consider it crucial if you just want to get going.

 

There is also a youtube showing how to do this:

 

Good pics:

image.jpeg.70a4e1e2af7fa635d0047261f03aac66.jpeg

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Yeup, I've watched that video too 😊

I think I've got my mind wrapped around it.  My mechanic is lending me his degree wheel, piston stop & dial indicator so I can make this happen.  Now my curiosity has gotten the best of me so I'm gonna give it a try.

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