Jump to content
jagman

My 720 smokes more than I do!

Recommended Posts

I overheated the truck.  Replaced the head gasket and noted the antifreeze incursion  in cyls 2 and 3.  I also replaced the pcv valve and replaced the original carb with a weber. All appears normal and timing is now spot on.  I fired her up and she smokes (oil) on deceleration at speed ( 35-45 mph).  Will this clear up with use?

Share this post


Link to post

A few questions:  How do you know its oil?  Did you surface the head before replacing the gasket?  Is the coolant level remaining constant? 

Share this post


Link to post

I'll assume that it didn't do this before and it's a new symptom. Very possible to get coolant and oil into the cylinders and exhaust manifold when changing a HG. A half hour drive should burn all trace of it out.

 

1/ I would check the oil and the oil level. If coolant got into the cylinders some of it also got past the rings and into the oil. Water will sink to the bottom and the oil float on top raising the level to where the crank may splash it onto the cylinders and over load the rings. On deceleration combustion chamber vacuum is very high and oil might get sucked up past the rings. If the oil is cloudy change it and the filter.

 

Possibly also the head is warped and leaking coolant into the 2 or 3 cylinder and you're seeing coolant steam

 

2/ Another source of oil are the valve guide seals. Over heating may have finished them off and oil will run down the stems and into the cylinder and / or the exhaust manifold. New ones are a couple of bucks each and can easily be replaced with a spring compressor and a piece of rope with the head on.

 

3/ The head is warped badly in or around the 2 and 3 cylinders. This is also where the oil from the block enters the underside of the head to lubricate the valve train. Oil may be getting into one or both cylinders.

 

 

Share this post


Link to post

Did you check the head and block with a machinist straight-edge?

Edited by DIY 1985

Share this post


Link to post

I did check the head with a 4 foot machinists rule and it is straight.  I took it out for a 20 mile drive and found that the smoke dissipated after 6 miles. I again drove it the next day after putting in two quarts of oil and the same thing happened.  The oil ( no antifreeze, the oil was changed) still appears to run out of the back of the engine but not from the area of the head or head gasket, that is dry.  I have it timed for 5 degrees btc with no vacuum to the distributor as per your specs but she acts as though I have it too advanced when starting. Running, she has all the performance I could ask for. The oil leak is the bug in my soup now.  You could say that I am the turkey of the day. 

Happy Turkey day!

Share this post


Link to post

Two Quarts in 20 miles!!!!!! You said smokes. A leak is different.

 

Leak is between the engine and transmission at back of the oil pan???

Share this post


Link to post

The smoking stops when the engine is run until hot. It might quit altogether if it is because the cylinders were scoured by the steam from the blown head gasket.

The leak appears to be  between the engine and transmission.  It leaks when sitting and must leak more when running and with the new carb it runs very well.  Do I have a blown rear seal?  Can I put one in without pulling the engine? 

  • Like 1

Share this post


Link to post

The entire underside of the truck must be oil covered. Probably on the exhaust and it burns off.

 

If lucky it's the pan gasket but might be easier to pull the engine to do a good job with that... and then you may as well change the rear seal anyway. The flywheel has to come off for this.

  • Like 1

Share this post


Link to post

I will try to get the truck on the lift to check the pan and determine where the leak originates. I was hoping for a warm up but thats not happening soon!

  • Like 1

Share this post


Link to post

Check your oil filter.  I have had problems with the NAPA Gold filters not sealing.

Share this post


Link to post

Maybe the rubber gasket fell off or the old one stuck and you have two on it.

Share this post


Link to post

I got her up on the lift today and cleaned the entire bottom of the truck  (oil everywhere! ) and found the leak to be dripping from the metal plate that appears to be the front of the transmission.   Two other folks looked at it and their observations were "it's the rear seal or the rear of the pan gasket".  I checked the bolts on the pan and they are tight.  I also climbed up and started the truck and the drip became a piddle.  It looks like I will be pulling the transmission.  I am hoping that I can replace the pan gasket and the rear seal when the tyranny is removed without having to pull the engine. I will also get a complete clutch kit for reassembly.  Any advice would be appreciated.

Share this post


Link to post

The oil sender is not leaking nor is the filter, so I am going to begin the disassembly process today with great trepidation.

I will fly the banner of stupidity because there is no law against it!

Share this post


Link to post

I am just about to pull the tranny but have lost the little circlip that holds the shifter together.  Where can I get one  to fit?

Share this post


Link to post

Take the pin into a hardware or fastener store and look for an 'E clip" that will fit.

 

Nissan may still have it. The number is 32854-24900 used last in '86.5.

Share this post


Link to post

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.

Guest
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.

Loading...

×
×
  • Create New...

Important Information

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