85 z24 random knock and stutter.

[ElliotV]

So today when I got home from work I ate lunch and then went to leave for school 20~min later and the truck started to make a bit of extra exhaust noise like it started leaking at a gasket or something and then I tried driving and it was acting weird sort of shaking and stuttering when I was just starting off and sounding like it was missing hard. I backed up to my house and when trying to quickly diagnose it I blipped the throttle really quick and I head 2 knocks when coming up to rpm and not like rod knock like ignition knock. Withing the past 10k miles I have done ngk spark plugs new wires and cap and rotor. I'm really unsure of what would be causing this but I have a couple thoughts but I'm hoping it's nothing internal. 

 

I'm thinking it's either something has fallen apart in the distributor causing the 'lack of power', timing guide taking a dump and causing the exhaust and intake blades to open late(feels unlikely to me because when I had the valve cover off the timing chain and cam gear had very little wear for 160k), or perhaps the carb has taken a dump? The truck has all the stock Hitachi and emissions crap on it still so it's possible over 40 years that it's just given up?

[NC85ST]

If I understood correctly, you said it sounded like it spark knocked. I would say that you’ve probably have a blown head gasket, but I hope I’m wrong.

[ElliotV]

15 minutes ago, NC85ST said:

If I understood correctly, you said it sounded like it spark knocked. I would say that you’ve probably have a blown head gasket, but I hope I’m wrong.

Yeah I sat and thought about in class and the more I think about it the more it makes sense. More air getting pushed out of one of the cylinders making the exhaust seem like it's louder and it would cause a stutter and lack of power. I'm going to pick up a compression tester after school and pull the plugs and do a compression test. The motor never got hot and I even have a aftermarket inline gauge to keep a eye on it. If it is blown then I do have 2 other trucks with viable motors so I will probably debate swapping them or just doing the head gasket. 

[datzenmike]

Are you aware that the head gaskets can blow at approximately 100k intervals? and the factory recommends re-torquing the head bolts once a year? A blown head gasket is possible at 160k.

 

A compression tester may show two adjacent cylinders lower than the other two.

 

Perform a leak down test which is much more definitive. Gaskets tend to blow between cylinders at the narrowest point between them and the compression seesaws back and forth between cylinders. If this is the case, two adjacent cylinders will test low and more importantly, there will be a hissing sound out the carburetor from the other cylinder's open intake valve that can be heard at the open end of the carburetor.  

 

 Sometimes they can blow into the cooling system which can show as bubbles in the coolant if you look with the rad cap off and idling. This compression in the cooling system can over pressurize the rad cap and push into the coolant recovery bottle so watch for unexplained coolant loss. Last, coolant can be boiled to steam and the exhaust will smell sweet with antifreeze.  

[ElliotV]

4 minutes ago, datzenmike said:

Are you aware that the head gaskets can blow at approximately 100k intervals? and the factory recommends re-torquing the head bolts once a year? A blown head gasket is possible at 160k.

 

A compression tester may show two adjacent cylinders lower than the other two.

 

Perform a leak down test which is much more definitive. Gaskets tend to blow between cylinders at the narrowest point between them and the compression seesaws back and forth between cylinders. If this is the case, two adjacent cylinders will test low and more importantly, there will be a hissing sound out the carburetor from the other cylinder's open intake valve that can be heard at the open end of the carburetor.  

 

 Sometimes they can blow into the cooling system which can show as bubbles in the coolant if you look with the rad cap off and idling. This compression in the cooling system can over pressurize the rad cap and push into the coolant recovery bottle so watch for unexplained coolant loss. Last, coolant can be boiled to steam and the exhaust will smell sweet with antifreeze.  

Yeah I know these engines like to blow head gaskets that was what had been done to the engine in my 86 before I bought it and they did the head gasket and I put the rest back together and now that one is running. I'm going to pull all the exhaust plugs and run a compression test on it. The idea is that it will show really low compression on any that are blown between each other since there will be nothing to stop air from leaking out of the other affected cylinder. I'm really hoping it's not a head gasket but the more I think about the more it seems likely. Do you happen to know if anyone is selling the timing chain wedges for these trucks? I'm sure I could make one but would rather not if possible.

[ElliotV]

Welp definitely a blown head gasket 3 was 40lbs and 4 was 30lbs 

[datzenmike]

I've always used wedges but I don't like them. It relies on friction and hammering it in tight enough. Would prefer the plastic tensioner blocker. I've heard that a folded length of garden hose shoved down between the chains will work. Has to go all the way to the crank shaft sprocket.

 

[ElliotV]

18 minutes ago, datzenmike said:

I've always used wedges but I don't like them. It relies on friction and hammering it in tight enough. Would prefer the plastic tensioner blocker. I've heard that a folded length of garden hose shoved down between the chains will work. Has to go all the way to the crank shaft sprocket.

 

I have found this one but it doesn't appear to go far enough down

https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChcSEwi39srry9WJAxXAH60GHbeSMdEYABAMGgJwdg&ae=2&aspm=1&co=1&ase=2&gclid=Cj0KCQiA88a5BhDPARIsAFj595hPKgd8QXesRXH3K2rcDZzcc_iCA3s2Fm-MgJEJqqWY3LRo_PPgt8kaAqI6EALw_wcB&sph=&ohost=www.google.com&cid=CAESxAHg9uPiqnWV9IWuQuGBUxUj0oN8xSITjiBrWcVQQ4slDTQnAtwcEIUcM8mVp95xhMCVak46CUfYNOzCvy6SWuZsvrrzxOvauEMIfjoqV8VEq3BuH_vdfG1iVhEU3V29FGIjEft_Ca7xyc_HPuFAYwpEiktRwHRPnwj3ikqpeJridMpLkVR5aZ1gNo-hbk65cySkbFwKg8yF-KNSHZdFy7jycakQwlaHVh64VhBsbYFHHPAptbAm2ZyQF0NGS96VXWbctLDw&sig=AOD64_1VDZh4r4Di7nrNfIYxDQZ_f0N4Lg&ctype=5&q=&nis=7&ved=2ahUKEwj888Try9WJAxWROTQIHWGiB2MQwg8oAHoECAgQDA&dct=1&suid=27306093434&ri=27&adurl=

[datzenmike]

Yeah, that's a wedge.

[ElliotV]

12 minutes ago, datzenmike said:

Yeah, that's a wedge.

Alright I got that one on order and have a head gasket set coming in tomorrow too. Hopefully I can get this taken care of soon because even though I have some more modern vehicles that I could drive I just love driving this truck and it's treated me good over the last year as a daily.

[NC85ST]

20 hours ago, ElliotV said:

I have found this one but it doesn't appear to go far enough down

Yeah, I tried that one and ended up taking the timing cover off my engine. The only positive thing about it was, I sat the head back on and made one out of wood. It worked great. 

[ElliotV]

14 minutes ago, NC85ST said:

Yeah, I tried that one and ended up taking the timing cover off my engine. The only positive thing about it was, I sat the head back on and made one out of wood. It worked great. 

So I should just go ahead and make one out of wood then since the one datzun mike has is no longer for sale?

[RLJ]

https://zcardepot.com/products/timing-chain-guide-retainer-tool-240z-260z-280z-280zx?_pos=1&_sid=b6ff1196f&_ss=r

[ElliotV]

1 minute ago, RLJ said:

https://zcardepot.com/products/timing-chain-guide-retainer-tool-240z-260z-280z-280zx?_pos=1&_sid=b6ff1196f&_ss=r

I'm going to order that right now. I'm going to do the head this weekend and have a head gasket coming from Nissan themeselves.

[ElliotV]

well I got the intake off today since I pretty much only had a half day but I did manage to break all the exhaust manifold bolts loose with no problem so that is a win. I also picked up a new alternator for a 89 240sx for a alternator upgrade since the alternator is right there anyways I thought why the hell not. Still waiting on my wedge to come in from USPS so I will not be finishing it this weekend sadly. I have decided that I will be replacing the valve seals on the head since I will have it off anyways as well. 

 

Also does anyone trust fel pro head gaskets. The nissan one I ordered came in and they folded the front corner by the timing chain so I'm not sure I should use that one or just use the fel pro gasket or try to get them to send me another one.

 

[datzenmike]

FelPro are fine. The front around the timing chain only seals in oil spray and fumes. You could smear the thinnest amount of RTV at the fold, install head and wipe off what squeezes out.

[ElliotV]

1 minute ago, datzenmike said:

FelPro are fine. The front around the timing chain only seals in oil spray and fumes. You could smear the thinnest amount of RTV at the fold, install head and wipe off what squeezes out.

I will probably just run the fel pro gasket then and get my money back out of the Nissan gasket if I can't get another one in time. Just really annoyed that someone would go through the effort to ship something and forced it into a box like that.

[NC85ST]

Just FYI for future reference, you don’t have to take the intake off to remove the head. The bolts for the intake are a real pain with the head still on the engine. If you want to save yourself a lot of time and effort, before you put the head back on, bolt the intake to the head first.

[ElliotV]

9 minutes ago, NC85ST said:

Just FYI for future reference, you don’t have to take the intake off to remove the head. The bolts for the intake are a real pain with the head still on the engine. If you want to save yourself a lot of time and effort, before you put the head back on, bolt the intake to the head first.

I will likely be installing everything as one unit but the reason I took it off yesterday was #1 it really isnt that bad to do all in all because most of the time was spent disconnecting stuff from the intake itself and the intake really isnt that bad to take off this is the second one I have done and yes a couple bolts aren't very easy but they wouldnt be too much easier with the head off becuase usually it is the intake that is in its own way and really I could only see the bolts better if the head was off. #2 With the intake off and then the PS pump it will be easier to get to the alternator to upgrade since I figured my wedge would be late.

[datzenmike]

Make sure the dowels are in the front and rear left side head bolt holes. These will locate the gasket and align the head in place.

 

You took the hood off, right? Makes taking the head off/on with manifold/carburetor in place way easier with help. Two can easily drop the head in place with the intake on.

 

Do not lay the head with the combustion chambers facing down. Some are open and it's a good way to bend one. Set on blocks of wood.

 

Check head surface is level or you'll be doing this again. It's just insurance.

 

Mark chain and cam sprocket so there is no guessing when assembling.

 

Replacing valve seals? Keep in order. Check rocker surface for wear and start using an oil with high ZDDP content such as Shell Rotella T4

 

 

 

 

[ElliotV]

2 minutes ago, datzenmike said:

Make sure the dowels are in the front and rear left side head bolt holes. These will locate the gasket and align the head in place.

 

You took the hood off, right? Makes taking the head off/on with manifold/carburetor in place way easier with help. Two can easily drop the head in place with the intake on.

 

Do not lay the head with the combustion chambers facing down. Some are open and it's a good way to bend one. Set on blocks of wood.

 

Check head surface is level or you'll be doing this again. It's just insurance.

 

Mark chain and cam sprocket so there is no guessing when assembling.

 

Replacing valve seals? Keep in order. Check rocker surface for wear and start using an oil with high ZDDP content such as Shell Rotella T4

 

 

 

 

I have been using zinc supplements and 10w-40 oil in this truck and changing the oil every 2k miles. I am definitly checking the head and if there is any question I already had a shop quote me 200 bucks to just do the seals and deck it. I have not taken the hood off yet but will be doing that whenever I can get someone over here to pull the head with me. I'm still not supposed to be doing too much since I decided to stick my finger in the bead of a tire and rim.

[datzenmike]

Get Rotella T4 in 15w40. It is available everywhere and 1,200 PPM ZDDP. No mixing or buying extra additives. You know that to much ZDDP is as bad as too little?

 

If the PCV valve is functioning in your Z24, 5-6K is fine for oil changes.

[ElliotV]

8 minutes ago, datzenmike said:

Get Rotella T4 in 15w40. It is available everywhere and 1,200 PPM ZDDP. No mixing or buying extra additives. You know that to much ZDDP is as bad as too little?

 

If the PCV valve is functioning in your Z24, 5-6K is fine for oil changes.

I'm not going to run 15w40 in the winter in this truck but definitely during the summer. Since I'm still running conventional oil I wouldn't even go past 3k but once I start getting past 2500mi I start burning a little oil so I figured I might as well just change it at 2k since it doesn't hurt to change it more often. 

 

This is what I'm running for a zinc additive.

[ElliotV]

Hey mike what is a good valve lash to set when the engine is cold once I get this thing torn down and put back together. I know warm is .014 but wondering if there is a recommended amount for initial startup.

[datzenmike]

Rotella T4 also comes in 10w30 so that covers the winter also. No mixing, no guessing.

 

Nissan does not specify a cold setting but at a guess probably 0.002" less. That's the problem with a cold setting it assumes a lot... like it will open up to the correct amount when warm. What is cold anyway? You might be setting it at 40,F 60F or even in the summer at 85F. A hot engine is always 180F.