345 Rebuild-quench, compression, cam

A

aeroron

New member
345 rebuild-quench, compression, cam:
*my ride: (my first post ever, hope this is ok)
1979 Scout II 345a, 727 trans, 4x4 with 3.54 gears, original 4bbl carter tq, original prestolite idn 4002r, emissions air pump, many oem options including a/c, cruise. Use is mostly for cruise-ins and enter in car shows, but also as a back-up daily driver. Use low/midrange power most often, but once in a while long interstate drives. (my other '79 is my rusty-trusty.)

*background:
I believe the engine is original and never been apart. The heads have never been milled (are 3.445" high/thick) and the bores are std. While the engine had some sudden problems arise requiring a tear-down for inspection, internal cleaning, and correction, it showed little wear and I was tempted to just re-ring it, clean it up and put it back together. However, that would have been marginal, and I would probably be sorry later.
So, I'm having the crank polished, heads redone with new valve springs, and guides machined to accept umbrella seals, etc. I'll be putting in silvolite 7082d.030 (can't get the +.020) w/sealed power rings (moly top) (hastings' warehouse is out of the top moly ring in this size).

*this brings us to my problem:
I wanted to keep this close to stock, and not make it "worse". I am concerned about the interrelationship of
quench (squish),
compression ratio,
and camshaft grind
with my carb, stock timing, etc. And available parts.

*what I have:
when I took it apart, I realized I should have made some measurements first, and stuffed #8 piston back in to see what I have:

piston deck height .040" (maybe .038" since it rocked).
Oem piston compression distance (measured with dial calipers) ~1.897" (note 7082d silvolites are 1.891", so this might make a new deck height without machining of .046"??).

Old embossed steel head gasket compressed ~.026". Gasket hole area is 82.13 cm^2 (to calculate cc's later). New compressed felpro will be ~.040"(?).

The above gave me a oem quench distance of .040"+.026"=.066". (seems kind of large to me for a quench-type chamber.(?))

I cc'd all 8 head chambers, got from 79.0cc to 79.8cc with 79.35cc rms average.
Head chamber hole area is 72.65 cm^2 (to be used for calculating change in cc's when milled).

I also took cam lobe and timing measurements for later comparison to a new one.

*where I'm headed(?):
I'm far from an expert or experienced, here, so I need help to decide what to do.

While the IH advertised cr for the '79 345a engine is 8.28:1, the above calculated volumes gives static cr~8.64:1. (perhaps IH meant dynamic, not static? If so, for marketing I would have used static.) since I had no problems previously with engine pinging with stock timing and a working egr, and sufficient pep for my uses, I would like to make sure I don't generate detonation or other problems with any changes.

I'm aware that keeping quench (squish) distance small is my friend to swirl the air and protect from detonation. To keep quench the same would require decking the block because of the thicker gasket (by .014") and maybe a lower piston height (by .006"?). From other forums here, it seems the expert opinion is to zd (zero deck the piston height).

However, several other things are at play here that concern me. To just get back the apparent oem quench distance of .066", the block would have to be decked .020" (still leaving a piston deck height of .026"). This raises static cr. In addition, my shop says I should have the heads milled--I don't know how much yet but let's say .010". This raises cr even more. My calculations show that the final static cr with decking, milling, and my .030"over bore is 8.893:1.

However, with a higher (static) cr I would think one would now especially want a little better 'quench" (smaller than the .066"). Am I on the right track? Suppose I pick a new quench height of .050". Then the block would have to be decked .036", and then the new static cr would be 9.176:1 (piston deck height .010"). Like chasing one's tail. I feel uncomfortable changing from the orginal that much, since I just wanted a stock or only slightly "better" ride before all this happened.

And to top it all off, I have to select a cam. I was thinking of the sealed power cs415 or clevite 229-1415 and new cht945 lifters. Having measured the cam that was in there, including its .006, .020 and .050 lobe lifts and its timing as best I could, these seem to be kinda' close to stock from what little specs I can find. However, I'm aware my "new" dynamic cr is affected by the previously proposed changes and the cam is part of this equation.
I noted the isky 190156 looks good too, but its spec has a .281" tappet lift for both intake and exhaust, and so would give a higher-than-stock .450" intake lift (rocker ratio 1.6:1), but also a whopping! .478" exhaust lift (rocker 1.7:1). It seems to me this is way too much on a slo-mo emissions (or even not emissions) IH.

What is your take on this? And what block decking and head milling and cam combo makes sense?

Sorry if this is too long of an introduction to my problem, but I thought I'd try to explain what I have and how I'm thinking. Like I said, I'm no expert. Please tell me where I am wrong (or right), or if there is another route entirely. Thanks in advance for your thoughts on this.
 
Last edited:
Congrats on the cool rig. I also have a '79 that had a sudden problem (head gasket) that necessitated (or not?) a rebuild. I figured since its history was unknown to me, and changing heads with the engine still in the rig was a pain, why not?

You're on the right track with the quench. That should be as tight as possible. .045" is about as much as I would go. I ended up decking my block and milling the heads to end up with both tight quench (.005" piston below deck) and 9:1 compression. Hindsight being 20-20, I should have offset ground the crank to extend the stroke and save the decking. You May want to consider this if the boat hasn't sailed on that yet.
For a cam, its hard to go wrong with the isky grinds Jeff sells here. I have the single pattern, .450" lift in my '74 and really like it. Great diesel torque, good vacuum, and mileage I can live with. My '79 got a comp cams piece that is good, but not blowing my dress up either. Should have done the isky.
Best thing to do is search the "rebuild" threads. Lots of people have gone down your road. Look up threads by Robert kenney. He's a moderator here and has plenty of insight. I'm sure he'll chime in soon. And also, call Jeff at the shop and pick his brain.
Take pics and keep us in the loop. We all like a good story!
 
Stock cr with your volumes works out to 8.3 when you add for piston crown to ring top volume. Abour .25 in^3.

Interrelation between quench distance and compression ratio?

Zero decking regardless of how you achieve it will increase your static compression ratio.. Unless you replace the non swept volume. The rest of your information is interesting and the first step in getting you a good setup..

Proper quench/squish band distance is .040-.045. Any bigger and it is worthless..

Silvolites for all intents and purposes are stock compression distance slugs. Dry assemble one cylinder on each side to see it you need to machine the block and even it up also to determine where you need to go.

The most conservative approach would be to create a optimum .040 quench with fp head gaskest, do not mill the heads but only to clean them up. Run the isky 156 cam. Lift is not the problem with emissions of low end performance, duration is. Also adding duration will require a bump in compression to compensate, which you will get from .040 quench and boring .030 over. Should make a nice runner.
 
Last edited:
Thanks for your responses. I ordered an isky 190156 today.

The machine shop said they already took off .010" from the heads to clean them up. I was hoping for less, but oh well... (with a 'minor' valve seat dressup job maybe I get back to an effective .007" milled as far as head cc's are concerned?)

thanks for calling my attention to my error: I forgot to add the piston crown-to-cylinder volume above the top ring in my calculations. My crowns measured ~3.854" diameter in the 3.875 bore (I forgot to check ring-to-top, but estimated from memory at ~.5"). This gives me almost a third of your .25 in^3. (of course, at room temperature.) using your .25 in^3 I do get a cr of ~8.3 as you said. If I put my .067 in^3 in my calculations I get an original 'static' cr of 8.55. If I then zero deck the block later to ~.002 piston in the hole, I calculate a static cr of 9.22 with my .030 bore. More than I was looking for. (using your .25 I would get a new cr of 8.96.) either way, (since it's the dynamic that counts) I hope this will still be good for 87 octane and the same prestolite's timing. If needed, I’m not sure I can recurve it, or even know how to do so properly. Comments on this would be welcome.
 
I personally don't know if calibration parts are available for the prestolite distributer. But to start with limit the total mechanical timing to 33-34 during engine break-in. After you put some miles on it and are comfortable leaning hard on it see if you can hear any pinging/detonation. The bigger cam should like around 2-4 degrees more initial timing than stock but watch total.

Compression can be funny when trying to determine how far to go.. The 156 will run fine with 9-1 but only if you achieve .040 quench distance can you have a good chance of running 87 octane and good total timing.
 
You have been of great help. I have read a number of threads here and this is a great site. I showed some photos from this site of the rear cam bearing install to my machine shop. He found them useful. As I get more information, I am trying to stay ahead of the game and plan ahead for future steps. I hope this is not too many questions, but this is my first complete rebuild and I would like some other advice on:

valve seat pressure:
I’ll have to check to see if my shop already got springs. What seat pressure should I ask my machine shop to do on my new valve springs for both intake and exhaust for the isky 190156 cam? I’ve seen numbers like 70# and 80-85#. I think stock had a spring rate of 296#/in and I think I read they are typically compressed .2” closed, giving a seat pressure of only about 60#. At a oem .440” valve lift that would have been .640”x296#/in=189# at max lift. For the isky cam with a higher lobe and valve lift, is there a max or min recommended valve spring force at max lift (exhaust and intake different since different rocker ratios)? Again, this is just a show Scout that will do some interstate travel, so I don’t expect to make it a high rev machine.

Cam timing:
is the 156 cam properly timed with the timing gear marks aligned, or might I have to manually advance it a tooth? I think I can figure out how to check the cam timing with my degree wheel, but I would want to know what is best for my ride if it's not how isky timed it to my keyways.

Pushrod length:
since this cam is a higher lift, we will check spring binding, especially for the exhaust 1.7 rocker ratio. However, I am also wondering about pushrod length, and if the hydraulic lifters can collapse enough to accommodate my changes of perhaps .044” (when both cold and hot). I never did check how much travel the lifters had left to collapse or extend before I took everything apart. Have there ever been issues about this?
(where my heads milled -.010”, block decked possibly -.046, head gasket thicker by .014”, valves and seats ‘cleaned up’ total ~-.003 divided by rocker ratio = .010+.046-.014+.003/1.7 = a total of .044” change in pushrod ‘level’).

Quench with felpro gasket:
the new felpro composite head gaskets I just got measure non-compressed .046”-.047” thick (replacing the compressed steel .026”). As you suggested, I will have the block zero-decked or .005" 'in-the-hole' to my new 7082d silvolite pistons for a target minimum .040” +.005/-? Quench. I’m not sure what to expect in variation due to assembly tolerances, etc. Has experience shown that the gaskets consistently compress to not less than .040”?

Piston-valve clearance:
just curious, although it seems to me this should be checked somehow anyway: what is the piston-valve clearance in the 345 with the 156 cam when the cam is timed right (assuming original deck, head, gasket, etc.)? Or, do I have so much clearance it’s not ever an issue in the IH 345 engine (with emissions heads)?

Thanks for any info in advance.
 
Areoron,
you have a lot of data that looks pretty loosely stated. So lets just go on what historically works flawlessly for the engines I build for people. Yes happy people.

Valve springs need to be of a known variety eg the comp 961. Install them @ 1.800. Should yield just under 77# seat. That is very conservative and safe for your engine. I have no data of history on any other spring that I care to post here. I have run many others but for members here that are more conservative I'll leave those for the play ground. Remember the 156 lobe lift is .281 while the stocker is .225 from what I have measured in the past on nice stock cams. Suppose that could be off a small % but close enough. Use that to calculate the rough lift increase you can expect and you get 24% more lift.

Cam timing depends greatly on where you go ultimately on compression ratio quench distance and fuel quality.
9-1 .040 and current 87 octane regular I'd install it straight up.
Because I'd want a bit more hp and like to run more timing than most. For the same setup but leaning toward more low end and a bit less timing I'd install it @ 106 intake lobe cl.(4 deg advanced) which is where it should install with the stock marks and key location. I have yet to be happy with any grinder's IH cams and have made offset keys for them.
Note of warning: always degree the cam.

Pr length and lifter preload needs to be measured to know if you are ok with the stock pr's. .050-.075 lifter preload is perfect but .025 -.100 will fly.


You seem to have the compression ratio calculations down pat so crunch your numbers first. Don't just zero deck it without calculating your ultimate cr while zd or .005-.010 in the hole. Stick with 9-1 (give or take .1) max from what you say you desire to run as fuel. .050 qd is still ok but on the big side.

The fp composite hg crushes to .040-.042. I use .040.

With your setup piston to valve clearance will be huge. Lift at tdc (over lap) is less then .040 and the valves are tucked up in the combustion chamber .4". Even after the intake valve chases the piston past tdc you will have tons of room.
 
Pushrod length: @!$$%#^!

I'm back now. I've been away awhile. Also just had a big layoff scare where I work. They didn't select me this time around. Not yet, anyway. In the meantime, I refinished the entire engine compartment while I waited for my machine shop to finish. I got everything back, now. I'll post photos of some "curious" things I've found later.

I had been wondering about pushrod length, since the shop decked the block to .007 in-the-hole, milled the heads, and did a valve/seat cleanup. I had hoped the isky cam would compensate, since its base circle is .030" smaller in radius than the oem cam that was in there.
I put my pushrods in between a rocker and a lifter in a fixture on the bench. I checked all the pushrods this way, they differ .015" length shortest to longest. I have a pr checker from comp cams (7704-1), although it's got smaller radius ends than the IH pushrods do. I put the checker in my pushrod length fixture and adjusted it to where a pushrod length had been set. That way, even with a slightly different radius ball end, I can at least get a comparative length in my engine assembly to see if my pushrods will give the right lifter preload.
I installed the cam, lifters, heads, and rocker assembly temporarily. It turns out the demons are against me. For the pushrod that is the shortest, my left bank has lifter preloads from .073" to .098". The right bank has preloads from .098" to .143"! Longer pushrods would give up to .158" preload! I noted the johnson lifter has a total plunger travel of ~.185", and if it's like the IH lifters its internal port might be nearly closed before it bottoms. I did stick the shortest pushrods in the worst locations, and they really do disappear down into the lifter.
I want to shoot for .030 to .065" preload (although maybe I could accept anything <.100"?), so I guess I'll have to have smith bros. Make me some pushrods. Unfortunately, they won't all be the same length. @!$$%#^! If they can accomodate me, I'll get three lengths and some spares.
@!$$%#^!
 

Attachments

  • DSCF1494.jpg
    DSCF1494.jpg
    35.9 KB · Views: 2,527
I made a typo above, meant to say my target is .030" to .075" lifter preload.

Btw, here's my cam bearing installation. Other bearing oil holes were opened as needed to match passages. No need to grind away at rear oil passages like in a photo elswhere in this site, and the full surface area was utilized of all cam journals with the clevites properly positioned. (I had to buy another set and do rear again, since my machine shop put it in too far to the rear and ground it away at the oil passage. Another @$!.)
 

Attachments

  • cambearingrear.jpg
    cambearingrear.jpg
    63.6 KB · Views: 1,373
  • cambearinghole.jpg
    cambearinghole.jpg
    84.1 KB · Views: 1,299
Now that's it's mostly too late.. You can find out how sloppy I have been. :)

my data for the head gaskets is .038 and .042, depending on the brand. I, too, use ".040" as the number, since that works out to "ideal" quench and it's handy.

I offset grind the crank, then deck the block to get to "0" clearance. On my stroked 392, that was .036". On my new race mill, it was .050"-ish.

I have taken .036 and .042 and similar numbers off blocks without milling the intake and without changing pushrods.

I do have a 304 that we took so much off, the pistons come out .020" and we had to mill the intake for fitment.

I'm nuttier than most, and on valve springs, run bbc ls6 springs, and 350+lbs of open (iirc) pressure is normal for me.

I have a stroked 392 that is zero-deck, with an isky 256/262 grind. I run this in my 1t travelette, pulling 20,000 pounds in the mountains in the hot summer.. And I run 85 octane.

This is on a 406cid engine at 9+:1, but over 3 or 4,000ft in altitude. It does not ping.

I know you don't want anything too wazoo, but my take is, it costs so much to a) build and b) operate these engines, that you might as well go all out and enjoy it more. :d
 
Probably to much duration unless you plan on some significant improvements.
I like this cam for a more stock build but still keeping compression in the 9-1 range. https://www.ihpartsamerica.com/store/isky-190125-26.html The important things to look at are duration @ .020 (202 and 208) and lobe lift .281.
Remember the stock cams were roughly 188 duration @ .050. Moving to 202* @ .050 is a big change in rpm and peak torque rpm location.

Please start a new thread so we can focus on your build and variables that are critical to cam choice.
 
You must log in or register to reply here.
Back
Top