Jump to content


Photo
- - - - -

L20b 86mm pistons


  • Please log in to reply
111 replies to this topic

#41 Kingcab

Kingcab

    Member

  • Members
  • PipPip
  • 62 posts
  • Location:Roseburg Oregon
  • Cars:Datsun 720

Posted 21 December 2017 - 03:44 AM

(Verified) they are the plugs you menchennd!

#42 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 72,566 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 21 December 2017 - 05:37 AM

Pull them and have a look at them. They may be fouled.

 

Black dry sooty is over rich

Black oily is oily

White or very light color is lean

Light brown or tan is just right


Posted Image

#43 Kingcab

Kingcab

    Member

  • Members
  • PipPip
  • 62 posts
  • Location:Roseburg Oregon
  • Cars:Datsun 720

Posted 26 December 2017 - 02:33 AM

Every thing that has been menchennd has been checked multiple times and still has the same problem.

#44 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 72,566 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 26 December 2017 - 08:42 AM

Pull them and have a look at them. They may be fouled.

 

Black dry sooty is over rich

Black oily is oily

White or very light color is lean

Light brown or tan is just right

 

What about the plugs? If the carb was swapped for another and still the same, we can (for now) eliminate the carb as the cause. Spark plugs are where the tire meets the pavement. You can't see them working. Do you have an old set you could clean and install?

 

Do you have the old cap and rotor and wires? Sure would be handy to swap them on and see it this fixes anything.


Posted Image

#45 Kingcab

Kingcab

    Member

  • Members
  • PipPip
  • 62 posts
  • Location:Roseburg Oregon
  • Cars:Datsun 720

Posted 26 December 2017 - 08:01 PM

I have used my new cap rotor plugs and wires and I have also swapped out plugs and wires and cap with ones I had laying around.

#46 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 72,566 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 26 December 2017 - 08:15 PM

Well maybe a bad valve then. Possibly that low cylinder?


Posted Image

#47 Kingcab

Kingcab

    Member

  • Members
  • PipPip
  • 62 posts
  • Location:Roseburg Oregon
  • Cars:Datsun 720

Posted 28 December 2017 - 01:28 AM

Okay guys I got a new head gasket and finely got it all back together started right up the studder in the idle has stoped it sounds really smooth now. But tomorrow I'm going to retune the carb and hopefully get the hesitation,while full throtle to stop. Any pointers would be greatly appreciated!

#48 Kingcab

Kingcab

    Member

  • Members
  • PipPip
  • 62 posts
  • Location:Roseburg Oregon
  • Cars:Datsun 720

Posted 28 December 2017 - 01:30 AM

Also there is a slight tapping it sounds like it's coming from the back of the head I'm going to double chek valve lash once again and see if it fixes it

#49 Crashtd420

Crashtd420

    Datsun Mechanic

  • Senior Member
  • PipPipPipPipPip
  • 2,135 posts
  • Location:Massachusetts
  • Cars:1972 Datsun 521

Posted 28 December 2017 - 05:07 AM

I'll be honest I'm surprised the head gasket was your issue... not saying it wasn't because the new one clearly fixed something..... and ya these heads are a little ticky, i think that's the nature of flat tappet cams....

I have a question for you.... what head gasket did you use the first time and the second time?
I ask because the ones that you can get from the parts store are for the l16,l18 and l20b and only up to a 85mm bore....

#50 Kingcab

Kingcab

    Member

  • Members
  • PipPip
  • 62 posts
  • Location:Roseburg Oregon
  • Cars:Datsun 720

Posted 28 December 2017 - 08:21 PM

Not sure on the brand at the moment but I just used a stock one and put it together the first time after the build and didn't realize my head was worped so re surfaced the head then reused that head gasket and the issue with the idle started. So then I got the same head gasket bran new and put it on and now it doesn't habe the idle problem anymore.

#51 Kingcab

Kingcab

    Member

  • Members
  • PipPip
  • 62 posts
  • Location:Roseburg Oregon
  • Cars:Datsun 720

Posted 28 December 2017 - 08:25 PM

With the stock headgaskets there is no overlap over the cylender walls with the 86mm bore at least with whatever brand I am using I will specify the brand when I get off work later.

#52 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 72,566 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 28 December 2017 - 08:35 PM

Yeah, you can't reuse a head gasket. It's crushed when torqued down and you can never get it exactly in the same place and seal. 


Posted Image

#53 Kingcab

Kingcab

    Member

  • Members
  • PipPip
  • 62 posts
  • Location:Roseburg Oregon
  • Cars:Datsun 720

Posted 29 December 2017 - 12:47 AM

It's a fel-pro head gasket

#54 Kingcab

Kingcab

    Member

  • Members
  • PipPip
  • 62 posts
  • Location:Roseburg Oregon
  • Cars:Datsun 720

Posted 29 December 2017 - 12:48 AM

But now I can't figure out why from idle if i floor it it has a huge hesitation and if I don't let off the gas it backfires out the card and dies

#55 Crashtd420

Crashtd420

    Datsun Mechanic

  • Senior Member
  • PipPipPipPipPip
  • 2,135 posts
  • Location:Massachusetts
  • Cars:1972 Datsun 521

Posted 29 December 2017 - 05:45 AM

With the stock headgaskets there is no overlap over the cylender walls with the 86mm bore at least with whatever brand I am using.

Well that's good....

#56 Kingcab

Kingcab

    Member

  • Members
  • PipPip
  • 62 posts
  • Location:Roseburg Oregon
  • Cars:Datsun 720

Posted 03 January 2018 - 04:12 AM

Figured it out!!! Not sure what it's called but it was part of the choke on the weber I was using. The piece with the blater on it was broken. Replaced it and tuned it and it runs better than ever!

#57 Crashtd420

Crashtd420

    Datsun Mechanic

  • Senior Member
  • PipPipPipPipPip
  • 2,135 posts
  • Location:Massachusetts
  • Cars:1972 Datsun 521

Posted 03 January 2018 - 06:53 AM

Figured it out!!! Not sure what it's called but it was part of the choke on the weber I was using. The piece with the blater on it was broken. Replaced it and tuned it and it runs better than ever!


Gotta luv it.... atleast it's fixed...

#58 Roadster-ka

Roadster-ka

    Advanced Member

  • Members
  • PipPipPip
  • 146 posts
  • Location:Vallejo
  • Cars:71 510 wagon

Posted 03 January 2018 - 06:57 AM

Blater??? Consider spell check.

#59 Kingcab

Kingcab

    Member

  • Members
  • PipPip
  • 62 posts
  • Location:Roseburg Oregon
  • Cars:Datsun 720

Posted 04 January 2018 - 03:25 AM

Right I Stoked I finally figured it out! I was wondering the best way to break in new piston rings and fresh bore.. also what oil is best to use??

#60 Crashtd420

Crashtd420

    Datsun Mechanic

  • Senior Member
  • PipPipPipPipPip
  • 2,135 posts
  • Location:Massachusetts
  • Cars:1972 Datsun 521

Posted 04 January 2018 - 04:03 AM

Oil anything with the high zinc... guys here like the rottella I believe.... I actually went the royal purple route they offer a HPS high zinc and phosphorus oil..

As far as break in the rings hasn't it already been running?
Basically now just drive it....
I actually broke my motor in on a dyno and all we did was a couple pulls to 2000, let the motor compression settle it back to idle then go again with a bit more rpm, but I was also breaking in a cam and stuff too.... once done I was making pulls to about 5500 ....
If your running and driving just go for a cruise vary the rpm and let the motor compression slow the vehicle and you'll be fine....
I'm sure I'll be corrected if someone disagrees...