Rering refresh???

[Bearwen]

Hello all,

I have read a lot of posts and have read some say to rebuild some say to leave the factory stuff in the bottom end and I'm wondering what I should do.

i have  130,000 mile 1979 280zx it has the 42 block and the 47 head. It ran and drove and didn't really smoke maybe a little we didn't drive it much just around the block brakes have issues.

my son did a compression check on a cold motor and did not open the throttle and all cylinders read around 120 give or take 5 lbs.

unfortunately We didn't do it warm and with the throttle open also after pulling the motor ( have chassis work to do) we noticed the valve lash was tight all were tight enough you couldn't get a .007 under any of them on a cold motor. Also the timing was a little retarded. Now the head is off and in the cylinders opposite of the piston skirt sides you can still see cross hatch in every cylinder and no big scratches but no cross hatch on the skirt sides on the skirt side you can see wear but not scars.

now we plan to put a megasquirt with newer style 20-25lbs injectors as well as a header and probably a custom intake as well as a 236 duration @.050 lift with a max lift of .460 cam.

we may boost it in the future at least a year from now.

my question is should we mess with the bottom end at all?

i read a post that tonyD says the factory stuff is better than anything after market and in that post he said if you do anything pull the rod and pistons and clean the ring lands so rings don't stick and put it back together and only replace anything that is noticeably bad.

from the looks of the insides of this motor I think it's in ok shape. So should I bother to pull the pistons and clean the ring lands and do I need to torque the rods with the bearings and measure them out of the motor or should I reuse the rod bearings?

this is a street motor and is only getting hopped up a little for street fun and what not it's is NOT a race motor.

so what do you guys think leave the bottom end alone take the rods out and clean the piston ring lands and reinstall with original rings and rod bearings or new rings and rod bearings and hone the block.

 

thanks for the replies

 

[grannyknot]

These are tough engines and 130K is not a lot miles, having the throttles open would have given you better idea but since all cylinders were equally starved of air and you had fairly consistent numbers you can probably leave it as is and save yourself some effort and money.

For me any excuse to rebuild the engine is a good reason but you will probably be fine by just resealing it.

 

You might want to pull 1 or 2 main bearing caps and conrod caps just to make sure.

[Bearwen]

So pulling the caps and then retorqueing them is ok?

should I put any assembly lube on the bearings when I put the caps back on or just some oil or leave them dry.

I have experience with old school chevy and ford motors and well those things when you pull a cap you replace stuff cause it's cheap but these nissans are suppose to be tanks.

[grannyknot]

4 hours ago, Bearwen said:

So pulling the caps and then retorqueing them is ok?

should I put any assembly lube on the bearings when I put the caps back on or just some oil or leave them dry.

I have experience with old school chevy and ford motors and well those things when you pull a cap you replace stuff cause it's cheap but these nissans are suppose to be tanks.

Okay technically, the main bearing caps should be loosened in 3 steps from the ends moving towards the center exactly opposite of the tightening sequence and to be safe that procedure really should be followed.  The conrods caps however can be loosened independently of each other with no harm.

Sure, I would throw some assembly lube on them if the bearings are in good shape and button it all back up.

I've always found conrod bearings wear out before the main bearings so if you check a couple of the conrod bearings first and they are good you may not have to touch the mains at all.

Personally I would find it irresistible not to go all the way, but if everything is in spec then rebuilding it isn't really going give much more than what you have right now.

[Bearwen]

 We are debating if we want to do anything as we have another motor and another z car.

we are thinking we will just put this one back together for now and just drive it and build the other motor up after we figure out what we want power wise and then we will rebuild this motor to go in the other car.

Father and son cars the one we are currently working on is son car so dads can wait. 

Thanks for the replies I may pull a couple con rods and see how they look.

 

so if the con rods look good and since I took them off should I run a quick bottle brush hone in the cylinders and put it back together ( after cleaning it ) and use the original rings assuming the cylinders are in spec.

 

Edited March 6, 2021 by Bearwen

[grannyknot]

3 hours ago, Bearwen said:

so if the con rods look good and since I took them off should I run a quick bottle brush hone in the cylinders and put it back together ( after cleaning it ) and use the original rings assuming the cylinders are in spec.

Absolutely not, those existing rings are perfectly mated to the cylinder walls just the way they are, if you deglaze then you have to put new rings in..

[Bearwen]

That's what I figured but i wanted to double check.

 

thanks again for the replies.