1984 720, piston slap? How long do I have?

[Stewart]

I moved this to a new thread in case it’s useful to someone.  Here is the old one for background.  Thanks to everyone who has been helping my meager mind grasp the mechanics involved!

 

I ended up taking it back to my mechanic to look at again.  He played with the valve lash as well and it didn’t change much so he did a compression test and got 125 psi on #4 and 175 on 1-3.  This is after a new head gasket and all the other associated gaskets.  He reminded me he had observed a small sliver of material missing from the top of #4 piston (missing from the edge on the exhaust side).  He thinks that is what is causing the noise (probably made noticeable after the cylinder hone on the head, which probably wasn’t really neccesary), there is just enough clearance for it to rattle a bit now.  That and the lower compression there is what is causing the spark plug to be a bit dirtier than the others.

 

So barring an engine rebuild that I don’t really have the funds/skills for, how long can I run it?  It drives just fine other than the clicking noise.  It’s a camper though and we like to get off the main road and don’t want to break down unexpectedly.  I don’t think it’d throw a rod or something though, it’d probably get worse slowly over time right?  Probably just start fouling that plug?

[datzenmike]

For $2,000 you could have had it rebuilt. Hell a re manufactured short block is under $1,500, a few hours to swap your alt, manifolds on and install it. Your mechanic should have at least pulled and replaced that piston, honed that cylinder and put new rings in it. Stay away from him.

 

I can't remember... did you pull the fan belts off and run it??? 

[Draker]

If it's piston slap, it would get worse over time. Who knows how long.. may take forever. Normally piston slap is worse when the engine is cold and will get a bit better when it warms up. If it's really bad.. you may not be able to tell a difference. That is if it's going from really bad to marginally less bad. lol.

 

If it got really bad, you would just lose compression. Maybe break a piston skirt or something. Could be bad if you are off road. We once took a 521 running on 3 pistons on a 200+ mile trip. Sure it used some oil.. but it didn't leave anyone stranded.

 

It's a gamble either way.. Do you have a video of the it running?

[Charlie69]

KA or VG it.  I like my Z24 but when it goes it will be tossed and a VG will be installed in my 86 King cab 720.  I want a little more power for towing.

[Charlie69]

My 86 wash getting a lot of valve lash noise and I got to thinking about my oil changes and I have been having surgeries for over 5 years now and I have had the local lube shop changing my oil.  I have been requesting Shell Rotella 15w-40 for it because of the high zinc content.  I went back to the shop and had the manager check their records and found out that they wear putting a high mileage semi synthetic oil in it in a 5w-30.  I live in Phoenix and with the summer time temps the 5w-30 is a joke in an engine with over 400,000 miles on it.  So I did an oil change with the Rotella 15w-40 and and a new filter and within the first week of driving the old truck I noticed that the valves were a lot quieter.  It is even quieter now about 3 weeks after the oil change.

 

Make sure your valve lash is set correct and put some Shell Rotella oil in your engine and see if it helps.  This oil is cheap at Walmart.

Edited September 5, 2018 by Charlie69

[datzenmike]

Piston slap is primarily a brief clatter on cold start up. It's for the most part harmless. If that piston is missing material from the top, however small, the rings or the ring lands below it may be damaged. If the bore is ok a new standard size piston and rings and hone the cylinder wall and you should be fine.

 

 

This sounds more like the chain rubbing something or the fan blade.

[datzenmike]

34 minutes ago, Charlie69 said:

My 86 wash getting a lot of valve lash noise and I got to thinking about my oil changes and I have been having surgeries for over 5 years now and I have had the local lube shop changing my oil.  I have been requesting Shell Rotella 15w-40 for it because of the high zinc content.  I went back to the shop and had the manager check their records and found out that they wear putting a high mileage semi synthetic oil in it in a 5w-30.  I live in Phoenix and with the summer time temps the 5w-30 is a joke in an engine with over 400,000 miles on it.  So I did an oil change with the Rotella 15w-40 and and a new filter and within the first week of driving the old truck I noticed that the valves were a lot quieter.  It is even quieter now about 3 weeks after the oil change.

 

Make sure your valve lash is set correct and put some Shell Rotella oil in your engine and see if it helps.  This oil is cheap at Walmart.

 

I've been on a 720 forum and it was mentioned that when a Z series engine is due for an oil change it starts making noise. Several found that the engine was always quieter after an oil change. I laughed at this but who knows?

[DrvnDrvr]

I put the Rotella 15w-40 in my 83 Z-24 for 3 years now and have never really noticed a change in the sound. However when I changed the oil in a 86 Toyota 22RE i had for over a decade it reduced the rattle in the front of the engine every time. Timing chain tensioner I guess. Who knows.

[bottomwatcher]

I use the diesel oil in just about every motor I have. The diesel truck and boat are expected but the lawn equipment, Datsun, air-cooled 68 bug and 4 stroke outboard all get the diesel oil at change time. The best part is autozone always seems to have one gallon jugs on sale for 14 bucks. The brand seems to change weekly but walk to the back and the diesel oil is usually half price from regular oil. Good news because the Duramax takes over two gallons. The diesel oil is the best bang for buck!