Going to rebuild. Concerned about what I'm starting with

[JQ02]

I have a '76 (VIN 2745571) with a non-matching block (2743228) and it looks like a 121 '69 head

 

When I installed a Mishimoto catch can I started having valve cover leaks. I re-routed the valve cover breather into a can and found that I was getting a ton of oily smoke - so lots of blow-by / very tired engine.

What are the chances that it's rebuildable - especially if I'd like to build a stroker?

(I'll definitely pressure test, etc., but hoping to reduce downtime)

Should I start looking for another block / head?

 

[Mike Self]

Obviously that engine has been messed with; normally a 121 head (used on 68-mid 72 engines--note the 1969 casting date) doesn't play nicely with pistons from an E12 ( mid-72 to 74/75 squarelights) or E21 (75/76 cars).  Your engine would have had an E21 head originally, so there's no telling what you'll find when you pull the head.  

 

Smoke on acceleration is generally worn rings; smoke on the overrun (coasting, throttle closed, in gear) is generally worn valve guides/stem seals.  Suggest doing both a compression test, then a leakdown test.  With the latter, hissing from the intake manifold = worn guides/seals; hissing from the exhaust = worn rings.  That'll at least get you started. 

 

mike

[Son of Marty]

Depending on the inspection results your engine can be rebuilt to factory specs, you'll  most likely need new pistons and a rebore and a head rebuild, then you need to figure out how many HP your after to select your cam and c/r.

[JQ02]

Thanks for your quick replies, @Mike Self and @Son of Marty. 

 

I was assuming I'd replace all the parts, given I want to do a stroker (+ cam, EFI, distributorless).

Does compression / leak down matter if I'm going to bore and stroke it?

If I replace the valves, guides, etc., what could matter if there are no cracks?

From what I've read, it sounds like the 121 matters for piston selection, but should be fine with the later block. Do I have that right?

I'm assuming my biggest risk is that the head has already been skimmed and there's not enough meat to do it again?

Given the unknown history of my engine, I may try to find another long block and give that to the shop so that I don't lose time after the engine's apart looking for another one.

[Conserv]

Agreed on all your points, JQ, but…

 

why do you believe “some other engine” is likely to be better than your current engine? They’re all 50 years old. Are you hoping to find an engine with 50 years of known history and receipts? Good luck with that!

 

Why don’t you break down your current block and assess it before you run off and buy someone else’s discard? At the same time you can assess your type 121 head, which would be perfectly fine for your purposes — if it’s not too thin, warped, or corroded. Some of the earlier 121 heads had smaller intake valves: I don’t know when the changeover occurred. Of course, with all the work you’re planning, that could be corrected if your head is so-equipped and otherwise good.

 

Presumably your “bore and stroke” are taking your new build out to 90, 91, or — God bless you — 92 mm. Overboring, and new pistons, can correct a lot of current deficiencies… 

 

That 2743228 block was probably cast around April 1976. You just need a crack-free block that doesn’t have too much corrosion in the jackets. With a stroker crankshaft, you might even be align-boring whichever block you eventually use. Again, and as you say, the comprehensive nature of your project doesn’t re-use a lot of wear components.

 

If your engine originally came out of a 49-state 1976 — the odds are with that over a California version — the original pistons (for the original E21 head) were flat-tops. That suggests that the 121 head could have worked with the block’s original pistons, so don’t be shocked if you find flat-tops.

 

Regards,

 

Steve

 

 

[tzei]

I was under impression that all 121 heads were 44/38 valved from factory. At least all i have encounterd have been so.

[Tommy]

21 minutes ago, tzei said:

I was under impression that all 121 heads were 44/38 valved from factory. At least all i have encounterd have been so.

No, not all. Most, maybe?

[Conserv]

On 9/11/2023 at 10:34 AM, Tommy said:

No, not all. Most, maybe?

Nobody seems to know the definitive answer. Some say 46 mm valves came to the 121 head in 1972-ish. That’s possible. Others say the difference between a 121 and a 121TI head is the valve size. I think that’s not correct. Anyway, it would probably be easy to upgrade valve size if your head’s condition warrants it!

 

Regards,

 

Steve

 

 

 

 

 

[JQ02]

Thanks very much, Steve! and @Tommy and @tzei

That's a fair point about using what I have.. I just like driving the car as much as I can and if I pull the motor, break it down, and then have to go looking for another motor, I'm further out from getting it back on the road. I don't have an endless amount of cash, so I think I'll take your advice and keep my fingers crossed. 

 

Thanks for the additional comments! Yeah. I'm thinking it's worth replacing the valves, so might as well go bigger if the head can take it. I'm assuming that the ECU mapping and injector sizes can help me sort out crank, piston, valve, cam decisions. I'd actually be pleased with a slightly lopey idle, so not worried about that. I'm talking to the machinist tomorrow and then can iterate through what makes sense and make sure I'm not putting together something that doesn't make sense.

 

If I only drive 2-3k miles / year and not tracking the car, I'm wondering if I can go 92mm and is it worth the risk for the 46 CCs? I'm sure this has been answered many times over. I'll do some reading.

 

I'm still hoping for feedback from someone that's done the IE Stroker crank. Seems like a fast (but $$$) path to 2.3l with 91mm pistons.

 

Also, I like torque, so not looking for bragging rights on HP. (which is why I was originally thinking m20 and am not as big on turbos)

 

I'm so grateful for the support of this community! 

 

Edited September 11, 2023 by JQ02

[TobyB]

While there is no replacement for displacement, 

you're only looking at incremental torque gains with a stroker.

 

So if you take the same amount of money you'd spend on the crank, etc

and spend it instead on cam, valvesprings, pistons, compression and tuning, would you make

MORE horsepower by winding it to, say, 7500 instead of stroking?

Would you like the zing more than the grunt?

 

As to where to start- me, I like keeping a running engine in a vehicle while I'm 

building its replacement.  And a 121 head's the lowest of the flow/detonation resistant

bunch.  So if you could find (ideally) an E12 or E21 donor engine, build that, then inject your 

current engine as a project, get it debugged, THEN put in a fresh block, THAT's going to give

you the best result.

Yes, get the bugs out of any induction system on an old engine.  

A. it's more tolerant of mistakes, as the cam's bedded, rings are sealed, bores are properly glazed, etc, etc, etc.

II.  if you blow it up, well, you weren't planning on keeping this one anyway.

 

my 02,

t

 

[JQ02]

That's a lot to think about, @TobyB Thank you.

If I go with bigger pistons and a header how relevant would the tuning on the old bottom end be?

 

I was thinking I could maybe do a supercharger (even later) vs. $3300 on a crank (now). Though then no ITBs.

 

And I think I prefer grunt over zing:) But of course both is better

Edited September 11, 2023 by JQ02

[TobyB]

Well, there's a supercharger (I have one from a baby Merc in the barn, just in case I need it)

and a turbocharger (I have a fistful of those, but only 2 on cars at present)

 

and both are LOTS of fun.  Me, I like turbo, because you can be all grandpa in town,

and then HELLION when the neighbors and the cops aren't looking.

Also, lots of plumbing.  Who doesn't like lots of plumbing?

 

The only down side is that if you plan on running real boost (over 1 bar) and yes, the M10 can take it,

then you end up having to run relatively low (9:1 or less) compression for detonation reasons.

Unless you go talk to PreYupy about some hemi pistons for a turbo car.  He's kinda good at that sort of thing...

 

t

 

[66m10]

Only 121 Tii heads have 46mm intake valves. The rest are all 44mm

[TobyB]

....that's been proven to be completely untrue for what's out there now...

 

t

 

[Conserv]

5 hours ago, 66m10 said:

Only 121 Tii heads have 46mm intake valves. The rest are all 44mm

Perhaps. But, if no 121 head ever received 46mm valves, there are certainly 121TI heads with both 44mm and 46mm valves. Many of us 🙄 have hoped to summarize and generalize the mysteries and applications of 121 and 121TI heads only to be proven wrong by… pesky facts. 121TI heads have been around since at least 1966, and many have 44mm valves. Below is a 121TI head cast in 1966. Smarter and more knowledgeable ‘02 guys than I have also claimed that (a.) only tii’s received 121TI heads, and, at other times, (b.) only tii’s got 46mm valves. Neither claim has panned out.

 

So, certainly, on this subject, I’m no longer claiming to know the whole story… 🙄

 

But I’m betting that any good 121 or 121TI head could be upgraded to 46mm valves without too much trouble!

 

Regards,

 

Steve