Jump to content

Compression dissapeared


Recommended Posts

I believe that was right I can’t remember but I’m fairly sure it was I really hope for no bent valves but probably did happen. Yeah the chain is tight it takes a crowbar and Some weight to get it onTo the pin. I had the eccentric tightened enough because the fuel pump was going since that was our method to see if the cam was spinning but it appears that only the sprocket was spinning seperate from the cam. 

Link to comment
  • Replies 133
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Way too many mistakes are being made here, questions are asked and either there is no answer or the wrong answer is given.

It also appears he is moving the crank with the wedge in there, I suppose that is possible but it may make it hard to get the cam gear on the cam.


I don't know how many times I can say this but I will say it again, turn the cam to 10am and 2pm, it may need tweaked a little when you put the cam gear on, but for now get it there and know it is there, don't guess or assume, know it, then get the crank to TDC with the rotor pointed at #1 plug wire on the distributor cap, don't put it anywhere except TDC, don't guess it is at TDC and the rotor is pointed at #1 plug wire, know it(turn it by hand), if you cannot do that put the L18 in.

Now it would be time to try and get the cam gear on the cam, first slide it on without the chain on it and look inside the #2 dowel pin hole, you should be able to see the end of the dowel in the hole, you should also not see a gap between the cam and the center hole of the gear, look at it as that is what it should look like, now remove it and put the chain on it and get it to where the #2 down hole is aligned with the dowel, you will have to keep moving the chain around on the gear till you get it aligned, then slide it on the cam and look to make sure the dowel is in #2 hole, then look at the center hole, is there any gap, if there is you may have to pry the cam forward and push on the cam gear until there is no gap, you have to know there is no gap, don't assume it, know it, you can put the fuel pump drive and bolt in and tighten it a little till it gets hard to turn, then remove the bolt and fuel pump drive and make sure there is no gap, if there is no gap put it back together and torque the bolt, if you cannot get the gear on the cam or get it on without a gap install the L18.

Now it is time to remove the wedge if you have made it this far, if you don't know about everything I explained above(TDC, 10am/2pm/rotor pointed at #1 spark plug wire) then install the L18, and what ever you do not pull anything apart on the L18 if it don't run right.


See how there is no gap.



See how the dowel is in #2 hole.


  • Like 1
Link to comment

that's sprocket mike posted is what Scapson installed hard to know if the cam is timed as the holes to see the V notch are in the wrong spot. That's why I say get the Jap made sprockets.

However if he marked it before he took it off he is OK.


Yes one isn't to move the crank once its off.

that why I always put it back to final TDC once the bolts are loose then take off head ect…..

  • Like 1
Link to comment

Update the new sprocket comes Thursday and there’s no bent valves because none of the valves were fully down so yay me for reading the book wrong. I’ll post an update Friday possibly depending on how it goes on Thursday after work I should hopefully have my datsun back I missed it. 

Link to comment

Then it’s probably the distributor timing either way I’m going to check the TDC in just to do be safe Incase it was off A little a well timed motor is best. Yay it runs ya it idled for a couple seconds yay my datsun yay no more Chevy van 20 yay no more fear of hitting something.  

Link to comment

I just fired it up and it’s backfiring like a son of a gun like it had 2 or 3 normal fires and then 1 backfire I have no idea what it is. It’s all timed perfect like TDC is 100% the cam sprocket is nice and tight it’s tight enough to spin the motor over. I’m at a loss. 

Edited by Scrapson
Link to comment

I take it back I had 2 and 3 cylinders swapped it’s kinda idiling but it was running off of either I had in it so it’s hard to tell and it was shaking like a son of a gun but it might’ve been from the lack of fuel I guess so time to put fluid in the radiator tighten the valve cover and go around the block. 

Link to comment

1342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 13411342 1342 1342 1342 1341


It's running on only 2 cylinders. The middle cylinders are firing at the top of the exhaust stroke and doing NOTHING.

  • Like 1
Link to comment

Runs good has power everything is good but I have a vacuum leak that’s bad like it’s suffocating on air right now I have to be on the throttle to keep it alive. It idles then dies down a bit and bit more I’ve tried adjusting the air fuel mixture I’ve rejetted it again with the original ones I had which were richer but it’s still not right. We revved the piss out of it at work like 4 and half grand plus and it blew a little smoke but no blue so that’s what I wanted. I’m going to adjust valves but why does it have a vacuum leak between the intake manifold and head I had them both tested they are straight and flat no twists or bows they were torqued down to like 25ft pounds I forgot but they are torqued in a outside inside pattern. 

Link to comment

You have a history of diagnosing engine problems that turn out to be anything but what you say. How can you possibly say a vacuum leak without some symptoms that support it and nothing else? 



Won't idle?


Check that the idle cut solenoid is on when running. Turn ignition ON OFF ON OFF (not start) and listen for clicking at rear of carb.

Take for 15 min drive pull over and look at ALL the spark plugs. Are they all even black? brown? tan? cream or white????? Plugs will show what mixture you have.

Get a simple vacuum gauge and tune for the highest vacuum you can at idle. Expect 18-22


  • Like 1
Link to comment

I haven’t reset the timing on the distributor yet I think I’m going to set it back 2° so it’s at 8° but not till I get the carb fixed so I can see if that’s why it won’t idle right because it has plenty of get up and go but not enough to idle around. I set the timing like 2 months ago now and it was fine it was timed to 10° With the vacuum advance disconnected. 

Link to comment

Idle is strongest when the timing is correct. Late or retarded timing sees the hot expanding gasses chasing a rapidly accelerating piston down the cylinder. To efficiently push down on the piston maximum pressure should occurs at or around 17 degrees after TDC where the combustion chamber and the space above the piston is relatively small. The L20B timing is 12 degrees and it will likely idle smoother and  stronger at 12 than 8.

Link to comment

So your saying to advance it 2°? I mean I guess that makes sense because if it is too retarded it will not ignite at the right time and then you’ll have either preignition or too late of ignition which can leak to the combustion cycle burning away at the head and gasket and block. Uh huh. 

Link to comment

I'm saying run the timing at what the factory calls for. L20Bs are 12 degrees I believe. Make sure your idle speed is about 750. Much higher and things like mechanical advance will automatically be added in and you don't want that.

Link to comment

you adjust the mixture at the base of carb to get it running best. turn in/out till runs best then time it also then set the speed screw.  the speed screw you should not have to tourn more than 1.5 turns if that to get the idle speed up to where you need.  My 521 its barely even turing it.  IF one has to turn the idle screw in more than 2 tursn your bypassing the idle jet and running on the main jet!!!!!!!!!!!!!!!!


ITS A FINE MEDIUM TO GET WHAT TOU WANT. I advance the dist and it will raise the rpm. but you need to see whats the timing then adjust the mixture or speed scre ect… back forth


ps over time it moves around a bit.  so readjust. timming and mixture.  mine changes abit also.I ajust for winter and then summer.

Edited by banzai510(hainz)
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.