Timing Chain Adjustment

[xofit]

Gooood Morning everybody, another quick question for you all today I ran my L20B with a Z head swap out of gas testing the fuel gauge and when it did die it decided to do so catastrophically and diesel backwards real quick resulting in my timing chain skipping two teeth. Shown here. Any advice on resetting the timing without taking the whole front of the motor apart? I have a few ideas including taking the front sprocket off and pulling it down while keeping tension on the chain to give space and rotating the crank to move the chain back into place. Any input is appreciated and incase I don't see ya good afternoon, good evening, and good night

[datzenmike]

 

Z head swap??? Looks like an L head to me!!!

 

Have never seen a timing chain skip or jump a tooth. Going to say that it's not possible.

 

Not seeing any 'proof' here. Do you mean the special link should be up higher like two o'clock???

 

 

Turn the engine over twice and bring up to TDC compression stroke #1... just like I assume you have. What do you see???

[banzai510(hainz)]

Are you sure?????????????????

 

You have to look at the v notch and the dash under the plate looking thru the sprocket hole.

set to TDC on the crank going cloockwise dial up to zero then look thru the sprocket and see.

 

what you might see is the link showing up where it is at that time it might take serval revelution to get back to where it LOOKS like when it was set up.

Meanign when one does this the first time you line up the links on the dimple of the sprocket at TDC and after one it 2 turns the links will not line back up right aways so one just checks the crank Zero and the V notch on the sprocket and dash

 

I assume truck still runs once you put gas in it.

Must like you have a weber DGV carb with out the cutoff selinoid(stock had the cutoff) and you sucking in gas when shutting down and it firing off.

Edited April 10 by banzai510(hainz)

[datzenmike]

Aww you're giving it away.

 

Run on is not the same as running backwards.

[xofit]

24 minutes ago, banzai510(hainz) said:

I assume truck still runs once you put gas in it.

That's the thing the truck does NOT run now, its blowing back out of the carb and will not fully start, at most I'm getting .5-1 seconds of running before it dies.

 

Also datzenmike this truck has already had issues with dieseling i misspoke saying backwards.

[Stoffregen Motorsports]

I don't know stock Datsun carbs very well, but some carbs will blow the accelerator pump or the power valve if they backfire through the carb.

 

Unless the chain was so badly stretched, it could not possibly jump a tooth.

 

Have a look down the front cover at the tensioner plunger. Is it poking out more than about 3/8 inch?

[xofit]

11 minutes ago, Stoffregen Motorsports said:

I don't know stock Datsun carbs very well, but some carbs will blow the accelerator pump or the power valve if they backfire through the carb.

So it does have a Weber 32/36 and we were having issues with bogging before and the belief was that the accelerator pump may have been going bad, as well as when the truck shut off it did backfire like a fucking shot gun but from my deafened ear i thought it had come from the exhaust. 

 

I also forgot to preface that this engine has somewhere in the range of 11-11.5:1 compression and runs off of a mix of 93 and leaded 110 just to prevent spark knocking. I'll dig a little farther into the accelerator pump idea though.

[xofit]

Realizing now I also forgot to mention that after trying to restart it I have been getting fire balls out of the carb... which is what lead me to believe timing had shifted in the first place. 

[xofit]

1 minute ago, xofit said:

Realizing now I also forgot to mention that after trying to restart it I have been getting fire balls out of the carb... which is what lead me to believe timing had shifted in the first place. 

Also tapped on the accelerator pump and got that working again but still no start condition.

[xofit]

1 hour ago, banzai510(hainz) said:

Must like you have a weber DGV carb with out the cutoff selinoid(stock had the cutoff) and you sucking in gas when shutting down and it firing off.

Could you expand on this at all?

[datzenmike]

Is this perhaps a Z24 block with an L head on it??? That would be close to 10 compression.

 

Look down the carburetor and pump the gas. If accelerator pump is working you should see a squirt of gas. 

Is the choke flap closed?

 

Engines will often backfire out the carburetor if the mixture is lean when starting.

 

 

Checks the plugs are dry and the engine is not flooded.

[xofit]

So yes I just check/ fixed the accelerator pump and the choke is open. And yes I do believe I had them mixed around in my head but the head is also shaved so it bumped it up even higher.

[xofit]

39 minutes ago, xofit said:

So it does have a Weber 32/36

This is wrong it has a Weber 38 DGAS apologies

[datzenmike]

To start cold you need the choke closed. If open it will be trying to run lean and that's the cause of the backfire through the carburetor.

 

 

Z24 with open chamber L20B head on it is 9.47. If you cut 1.75mm from the head you get 11 compression. That's 0.069"!!!!!!!!!!

[xofit]

Apologies for being all over the place with my info the truck just only recently came into my possession after 6 years of the motor being finished so I'm quite rusty on my info

[xofit]

Just now, datzenmike said:

Z24 with open chamber L20B head on it is 9.47. If you cut 1.75mm from the head you get 11 compression. That's 0.069"!!!!!!!!!!

This motor was previously a racing motor the guy that originally built it was a little out of his mind, bored over, decked heads, and a custom ground cam 😅

[Stoffregen Motorsports]

If it's totally flooded, floor the pedal and try to start it with the carb wide open.

[banzai510(hainz)]

do a motor timing check like in the vid I sent you. put motor at TDC and check the cam timing and then youll know if you jumped a tooth.

then look at your distributor timing and make sure its within reason of it being timed at TDC.

 

 

I believe the #*DGES can be made to install a idle cut off selinoid but thats least of the proplems right now.

Check timing and make sure the gas is in there. I would check my rocker arms, check for spark wires ect as this only takes a few minutes

 

to me back fire is out of time. Check inside the dist for loose parts . or maybe the dist is just loose and drifted to one side