best head

[hang_510]

you dont think the pistons were eyebrowed? def had work done at some point.

 

...something, and the tensioner fell out.

 

i drove the L20 w/o a tensioner for some time(~50K mi :eek: ). nothing catastrophic happened to it, but damage for sure w/many parts in the pan :mellow:

maybe thats how the block cracked??? :lol:

[datzenmike]

Nope. There's lots of stock piston motors out there with monster cams and everything clears the tops if timed correctly. You never hear of anyone doing this because it isn't needed. Besides they would look something like this to allow for the intake to be either on the back (#1) or front (#2) side of the cylinder.

 

http://i138.photobucket.com/albums/q251/datzenmike/L%20Z%20Heads%20and%20Motors/motorZ20EandZ20S720pistons4.jpg[/img]"]

 

It would be symmetrically cut... those all look different depths. And this is is a valve imprint...fucked!!!:

 

[sdsurf]

Now that is the help I am talking about...

1) should I use the pistons if the cylinders are good?

2) should I use the head and replace the valves or have a shop check the valves or pull the valves and check myself?

3) should I get a new head?

 

Thanks DatzenMike!!!

[datzenmike]

First, what do you know about that L20B block?????

The head you have... it's not from that L20B block is it????

 

Need more info.

 

 

 

Pistons look fine to me, maybe lightly sand down any sharp edges.

 

Did you clean those pistons that clean??? Because it doesn't look like it's been run much... too clean inside.

[sdsurf]

I know nothing about the block. pulled it from a 620 at the J/Y.

Yes that is the head from the block

Yes I cleaned the pistons but they weren't bad, actually really clean

[datzenmike]

Assume the timing chain was ok looking???? If so it was replaced and run OR tried to run and they gave up. If ran I would expect a lot more deposits on those marks on the pistons.

[sdsurf]

yeah timing chain looked good.

 

upon looking at the valves, they don't look at all like they were banging the pistons. Also, there is a different casting number on the head than the block so maybe it is a different head?

 

Assume the timing chain was ok looking???? If so it was replaced and run OR tried to run and they gave up. If ran I would expect a lot more deposits on those marks on the pistons.

[sdsurf]

Bump? Any response to my last thread?

[pl521sss]

yeah timing chain looked good.

 

upon looking at the valves, they don't look at all like they were banging the pistons. Also, there is a different casting number on the head than the block so maybe it is a different head?

 

You won't know till later if the timing chain is stretched or not.

And how much the head has been shaved off.

 

Block casting and cylinder head casting numbers are always different.

What's the casting number?

Bottom end is not something you can take apart once it's in the cartruck.

Cylinder head on the other hand is fairly easy if there's issue with it.

Just my thought if funds is an issue getting it serviced.

Sort of trial and error

[datzenmike]

The marks on the #4 piston would indicate a bent valve... possibly it was replaced. If so the motor was run afterward, or you would see marks on all the valves where the deposits would have been knocked off when hitting the piston tops. The whole head could have been changed also.

 

With all the timing guide plastic and tensioner springs in the pan, something fucked up since the oversize pistons were put in on the last rebuild, (dented pistons) or someone would have removed them while it was apart. The chain was likely replaced along with the other timing stuff.

 

Square or round exhaust ports?

[sdsurf]

it is a square port.

Is there a way to measure or tell if a head has been surfaced numerous times?

[datzenmike]

Yes. Measure down from the valve cover surface, the stock uncut head thickness should be 4.248" or 107.9mm

 

This is a U67 head, yes?

Edited March 2, 2009 by datzenmike

[sdsurf]

So I am thinking of leaving the block as is and getting the head worked on. What do you think my cost is going to be?

1) milling

2) valve job

[datzenmike]

Probably a couple hundred.You could remove the springs and lift the valve off the seat 0.413" and see if there is any sideways movement indicating valve guide wear. If they are snug just lap with compound if the seats look OK and install new seals.

[sdsurf]

I took a look at the engine today. There is no "ridge" at the top of the cylinder. The chain guides look relatively new and the cylinders look clean. I am debating leaving the pistons, rods, bearings and crank alone and get the cylinders at least checked out or pulling everything and going complete rebuild. What are things I might look for that would make me leave it alone? I have the "datsun rebuild" book and it is making me sway towards leaving it.

[hang_510]

I am debating leaving the pistons, rods, bearings and crank alone and get the cylinders at least checked out or pulling everything and going complete rebuild.

pistons are out = new rings and bearings, honing the block, at a minimum.

should be the plan w/an unknown JY motor.

 

the components are likely fine for re-use.

once you measure everything youll know better.

[sdsurf]

ok. So i pulled the pistons, rods, bearings and crank. The block and head are now at the machine shop getting the once over. So we will see if all is good!!:D

[sdsurf]

rebuilt head - $200

Block bored .040

new pistons

rings

bearings

magnaflux

cleaned

freeze plugs

 

all for $729 what do ya think?

[hang_510]

did ya get yer crank polished? :lol:

 

i think its assembly time!

[sdsurf]

dropped off my deposit today and it includes getting my crank polished :lol:

[datzenmike]

So where is the best head and crank polishing?

[sdsurf]

So where is the best head and crank polishing?

 

I hear there is good polishing in mexico;)

[72240z]

I hear there is good polishing in mexico;)

 

Ya and they throw in the std's and muggings at gunpoint for free WOOOOT :lol:.

[sdsurf]

got everything back and am using the U67 head I got rebuilt.

 

Here is the latest Dilemna:

 

I just picked up 2 A87 closed chamber heads. One had been milled at least once, the other has not. What are the advantages to the A87 vs U67?

Compression?

Power?

 

Give me all scenarios

[hang_510]

got everything back and am using the U67 head I got rebuilt.

 

What are the advantages to the A87 vs U67?

Compression?

that'd be about it... and a better 'squish' from the peanut.

since the U67 is done, dont keep changing your mind (it costs a lot to do that - uhhh dont ask!)

custom pistons to bump the CR if thats what you want.

i have an A87 notched for FI that will someday get used :D

 

the A87 ports are smaller, as are the valves (in stock config)

i have a ported A87 @ 1.5" that has damage on #3 CC(repairable) this would be a cheaper starting point for a build then spending the $$ to port your A87's.