are these parts stock?

[clutchdust]

guys, i know i'm going to get thumped but i spent the last half hour searching, so i need some help.

background: i come from the SBC world so this is my first L6 i've rebuilt. any suggestions you'd like to throw out there is welcome.

i'm putting together a mild little street motor for my '72 consisting of a '73 2.4 block and head but crank, rods and pistons from a 2.6 (unknown year, i just got the engine). i know the 2.6 was rebuilt at some point as it had been turned .020 on the crank and .010 on the rods already. the thing that has me a bit flummoxed is the pistons are flat tops with what appears to be near 0 quench. i thought the 2.4 and 2.6 both used a slight dish on the pistons. were 2.6 flat tops? i also noticed inside the sleeve has AMPCO cast into it. is that a factory nissan part?

if all this is stock, i should be looking at about 8.8:1 CR with the stock '73 (E88?) head, right?

if flat tops were not stock, any approximations on what the CR might be?

i'm tempted to throw in a compcams 260* cam while i've got all torn apart but don't think i want to put much cam on a <9.0:1 motor. not only that, but i think i'd like to put fresh valve springs on a new cam too, but don't know where to shop for L6 valve springs.

thoughts?

[Kennysgreen280zt]

I get 9.28:1 compression using the L26/E88 combo with no piston dish. That is based on a super old L-engine program I have.

 

I dont know if they are stock or not. are there valve reliefs cut in them?

[Dragonfly]

In the United States the 2.6L was only made in '74 and both of the ones that I have had in the past had flat top pistons. I believe what you have is all stock. Some of my knowledge in the L24 and L26 engines is getting rusty so I am not going to try to answer the rest of your questions, but I will make a suggestion that may help you out if you have a little time. Look for and purchase the HP book "How to Modify Your NISSAN/DATSUN OHC Engine" by Frank Honsowetz, it will answer the questions you have asked and many more, it also provides you with part numbers etc.

 

Dragonfly

[blue72]

Sounds all stock to me. You'll basically have a stroked l24 that displaces 2.6 liters (what the L26 was in the first place).

 

I'd love to calculate the compression ratio for you, but I'm missing a piece of information or two. In all of my searching so far I haven't found the head gasket bore for an L24/L26 motor. If you have some calipers handy and a minute or two I'd appreciate a quick measuring because I've long since been rid of my L24 stuff. I'd also need to know if you'll be running a Nissan or Fel-Pro head gasket (or other brand) because they differ slightly in thickness.

 

Oh, and does the E88 head you'll be using have this bump in the combustion chamber near the spark plug hole?

 

 

Since it's from a '73 I'm assuming it doesn't and that it has the redesigned chamber E88 head of August '72 and up.

 

Once I know those things I could compute what your motor's compression would be.

[clutchdust]

thanks, guys. i pulled the original 2.4 apart and seem to recall those pistons had a slight (1/8"?) dish. these are completely flat, no valve relief. i'll check the head when i'm at the shop tomorrow and post the results.

as for the head gasket, i know it's not a fel pro. it's out of one of those 'master' gasket kits, so it's fairly thick (thicker than i'd like).

i suppose if i can get over 9:1 on sCR, i wouldn't feel so bad about popping in that 260* cam. any thoughts on that?

don't know if i clarified in the earlier post, i've built several SBCs but this is my first L6. it's definately a budget build, but i'm looking for the best results i can get. what i have currently:

stock 2.4 block and 2.6 rotating assembly, assembled with hastings ring set and clevite bearings.

mildly ported stock head with hardened seats and new valves.

fresh chain and guides.

pertronix

arizona Z intake

390 holley

i'm still looking for (probably will buy from MSA) coated header. speaking of which, 6 to 1 or 3 to 2? maybe 6 to 1 since i'm looking for a more broad power curve rather than peak power.

i'm also ditching the mechanical fan and shooting for 200fhp or better.

what say you?

.

.

.

.

[EDIT] just checked and it is in fact an E88 head and no, it doesn't have that nifty "compression" bump cast in. (bummer).

[blue72]

As far as the "is it stock?" question, I dug through my old pictures and parts and here's what I found.

 

When I tore down my old L24E I found AMPCO cast into one side of the pistons as well.

The other side had a funny little symbol and some more numbers.

I noticed that same symbol was on the rods as well, so I assume everything was stock.

My L24E pistons had small valve reliefs cut into them as well. Note that these came out of motor L24-229575, from a '77-'79 Datsun 810.

 

The E88 cylinder head pictured in my other post is from my Z, a 2/'72 production car, so it had the 44.7cc chambers with their funny bump near the spark plug.

 

Okay, moving on to compression ratios. The listing I've found for later E88's states 47.8cc chamber size. My best guess on L24/L26 gasket bore so far is 86mm. Assuming the gasket is close to the stock Nissan HG in thickness we'll go with a 1.2mm compressed gasket thickness.

 

Crunching the numbers for all of the above combined with flat-tops gives me a 8.88:1 compression ratio.

 

You might like to know that the E88 head from the 260Z should have the same combustion chamber shape and size, but 2mm larger exhaust valves (35 vs. 33).

 

If you're looking for more power than stock, then the general consensus is headwork and cam (plus carb and exhaust, but I think you've got that covered already). You seem to be on the right track so far.

[2fast2Z]

If the head you have is from a L26 then try to look at the cam and see what it's stamped, if it have a C stamp you have a slight bigger cam, if you by chance have 2 cams you can send the other out for re grind, it's less than $100 at Delta.

Please take a look here:

http://www.atlanticz.ca/zclub/techtips/cam/index.htm

 

Chris

[Xnke]

Yes, the Ampco pistons are stock. I have dismantled 3 P30 blocks, and all had Ampco pistons with valve reliefs.

[clutchdust]

thanks for the input guys. the only thing that really threw me was the flat top pistons with 0 quench. when i pulled the original 2.4 apart i seem to recall they had the two valve relief (as did a previous 2.4 i had the head off).

i did notice the kind of trademarked symbol on the pistons as well as the rods. i think it used to be an old 'nissan' symbol.

the head mic'ed fine so i didn't have the machine shop mill it. now i'm thinking about doing that for the CR bump before i swap the cam. with an aluminum head (bare in mind i come from the SBC train of thought), i just think i'd like to have 9:1 or better before throwing any more cam at it.

would it make more sense to mill .005-.010" off the head or just get a thinner gasket?

[Daeron]

old?

[Dragonfly]

would it make more sense to mill .005-.010" off the head or just get a thinner gasket?

 

Personal opinion is the less material you remove from the head the better i.e. use a thinner gasket. No matter how you go about it since this is an overhead cam engine you need to be prepared to install cam tower shims in order to maintain the correct distance between the cam sprocket and the crank sprocket. You have some leeway but you do not want the chain tensioner to be sitting to far out of its base... because if it pops out for any reason your engine will be scrap.

 

From a engine safety aspect as far as the chain tensioner goes they (Nissan Motorsports) sells one with a sheet metal limiter on it so the tensioner shoe can not come out.

 

Dragonfly