COLLAPSED PISTON

[82Waggy]

I do believe that the designers of the AM V8 had a bit more knowledge than anybody here, and they got it right, with the exception of the oiling issue solved by the bypass line.

Bypass line is worthless, does nothing, can flow no additional oil unless gallery is blocked since pressure is otherwise the same at both ends - it is a closed loop back upon itself.

Only way to increase oiling to the mains is to increase system pressure or decrese pumping to the top of the engine with reduced ID pushrods.

[jeepsr4ever]

Actually the oiling line does something but its not at the end of the cycle its the begining. By forcing more oil to the back of the block it improves the flowback due to the mains being fed well and that where its primary benefit lies.

I would say the bore on this motor was wrong and it should be checked again.

[1980_Cj7]

Not that I'm an expert, but the way I understand it is
that forged pistons are for high rpm reliability, like more than 6500.
I think Perormance American Style says cast pistons are ok for up to that much.
So for the rpm's yu're looking for cast pistons should be ok.
But, cast pistons come with what ever dish volume they are,
whereas forged pistons can be ordered however you want them.

So lets see, you have a 401 .030 over with stock 58cc Heads right ?

9.208 Deck Ht., 3.68 Stoke, 5.858 Rod, alll nominal
So if we make a target Deck Clearance of .005 in the hole,
you need a piston with a 1.505 Comp Hieght,
and to get 9.5:1 compression, you'd need a 28cc dish.

So if my numbers are right you need a 28cc 1.505 Comp Ht Piston to get 9.5:1 Compression.
I believe stock 401 Pistons are 1.508 Compression Hieght.
Trouble is most aftermarket replacement pistons are shorter as you've found out.

Please let me know if any of the specs are different for the parts you have.

I think the cam you have would be ok with 9.5:1.
did you keep the lifters in order as to what hole they came out of ?

Let me know what compression ration you're after and your specs
and I'll do what I can to help and run calculations to help select pistons.

We're after whatever compression ratio is going to give us the most power and run on pump gas, even if we have to go to 94 octane.

.030 over with stock 58cc heads, correct. All the dimensions on the engine are stock. The Ross pistons we had trouble with have .145 deep 23cc dishes and have 1.493 compression height which puts them down the hole .017. Ross claims a 9.8:1 compression ratio with them.

We were getting pinging on 94 octane if we advanced the timing to where the engine would produce any kind of power. When timed with a vacuum gauge, it wanted 20 degrees initial timing (advanced to get max vacuum of 17" backed off 2" to 15", then checked with the light). At 15 degrees initial we were getting 35 total. The engine would crank very hard until you got the timing to 20 degrees, then it would crank over normally. With initial timing down at 10 degrees, the engine was deader than a doornail. The tired old 258 would have run circles around it. As I have been saying though, something seemed srewy with the timing on this engine. I did verify that the timing marks were correct.

We only picked forged pistons because they were the only ones we could find in the 9.8 CR that we hoped would give us a little extra power, but still work on pump gas.

[Blown7]

[quote="Holeshot"]Regarding the squirt holes in the rods, THE 1971 AMC technical service manual states, on page 2-10:

The connecting rods are stamped with the cylinder numbers in which they are assembled. The numbers are opposite the squirt holes and face the outside of the cylinder in which they are located. The connecting rod squirt holes in one bank lubricate the cylinders in the opposite bank

I knew that, I've got the same manual I purchased new in 1976!
Doesn't mean the engineers knew it all, you got to remember that engines were produced on a assembly line where time to fit all the parts correctly, and to basic tolerances was not a issue, time is the enemy on the assembly line. Squirter holes are a bandaid fix, we even have them on aircraft engines and Rambler had them back in the 1950's.


As for the pistons when you get to a corrected compression ratio of around 12.4 to 1 pump gas becomes a no go.
Corrected Compression Ratio = FCR - [ (altitude??1000) x 0.2 ] at 59 degrees F 29.92 inches of Mercury and don't forget your cam and it's timing will also play a part in your final compression ratio.



Jeff

[Blown7]

I do believe that the designers of the AM V8 had a bit more knowledge than anybody here, and they got it right, with the exception of the oiling issue solved by the bypass line.

Bypass line is worthless, does nothing, can flow no additional oil unless gallery is blocked since pressure is otherwise the same at both ends - it is a closed loop back upon itself.

Only way to increase oiling to the mains is to increase system pressure or decrese pumping to the top of the engine with reduced ID pushrods.

Ah heck, thats what blew your engine up, that damn bypass line.

[AMX69PHATTY]

Here is the compression ratio that an excel spreadsheet I made
comes up with using the provided numbers.
It comes out with the compression Ross claimed.



And here's what it comes up with for the Keith Black 354 Pistons
Shortened the Connecting Rod by .003 due to re-conditioning in these calculations


I'm not sure what was going on with the timing.
About 35 degrees total should be about right and
9.8:1 with 94 octane gas should work good without pinging.
I would stick with a dial back timimg light rather than the vacuum gage method.
The cam can reduce the engine vacuum at idle due to overlap.
Make sure the Distributor is properly phased, curved, and installed.

Sounds like to me you had everything picked out and set up right.
There seems to be agreement the Pistons were to tight in the bores.
Deck Clearance of 0.000 is optimum, but .017 in the hole should be ok.
There seems to be disagreement about the oil squirter holes.
Does anyone have old stock Rod Bearings in the size you need with holes ?
Can you put the crank, #1 Piston/Rod, Dampener, and Timing cover
back on the block and check the timing marks using a dial indicator
to indicate Top Dead Center on the piston and see if the marks line up ?

Has Ross agreed to replace the pistons ?
Or have you decided on replacement Pistons ?
If you're not going to be driving in the winter the AirGap would be good,
but due to larger runners it shifts the torque curve up some in the rpm range.
Make sure and use a fuel pressure regulator set to 5-1/2 psi.
Low engine vacuum makes a carb run rich, this can be fixed with springs or power valves.
Said you had an Edelbrock right ? May I ask the part number ?
Manual choke style is set up richer than the electric choke model.

So does everyone else agree that everything seemed to be set right ?
Other than the pistons being to tight and the timing wierdness ?
Reading through the posts it seems that way.

Man, 1980_CJ7, I hope you get it back together and it works out right.

[Blown7]

Speaking of the heads where they ever CC'd? To find out the actual chamber volume? And from the pics of the block it looks like it was decked (too shiny)

https://home.comcast.net/~rwsr50/Com...Piston_009.jpg
So that chart you have, may have errors made on assumptions.

Jeff

[FuzzFace2]

On the timing try another light as some ign. systems don’t play nice with some lights I’m told. You are running an HEI right every light should work with it???

I had a 304 that when checked with my light (snapon dial back) came up with 40* BTDC no vacuum. I checked the timing marks to make sure they where true and they where. The dist. was an old Mallory duel point with a mag. Pick up conversion, no box & steel core wires.
Thinking RF noise from the wires to the pick up and maybe the light I updated the ign system to MSD ( dist., 6al box, blaster coil, 8.5 wires) setup. Well even with the MSD setup light still did the same thing funny thing is light worked on my stock 75 v8 Gremlin!
Never did find out why it came up with 40* BTDC as motor got a knock so I built a 360 can’t remember if I put the light to it yet but motor starts faster & sound like it runs better.

Note to self: put timing light to 360 motor!
Dave ----

[1980_Cj7]

Let me try to answer everybody's questions.

Didn't use a dial indicator, just did it by feel, but I did bring No. 1 piston up to TDC with the head off, then checked the timing mark, and it was right on. I'm pretty comfortable that I had TDC even without a dial indicator because I went back and forth a couple times, then when I checked deck clearance with a feeler gauge, I got .020. Calculating mathmatically gives .017, so I'd say I was very close.

We have a Craftsman adjustable timing light. Ignition is stock with the exception of a Ford TFI coil. Good point on trying a different timing light. Never thought of that. That's what's great about these forums, two heads are better than one. Come to think of it, we did try a different timing light, well, kind of. Fuzz checked the timing at his place, but...he had the exact same model timing light we do.

The Edelbrock Performer 750 CFM carb was an electric choke, I forget the model number, but the whole choke assembly was removed and the holes where the shaft went thru were plugged with epoxy. We set it up for the base setting on the manual chart.

Not sure it the block was decked or not without checking the machine shop bill. It would seem it wasn't because the deck clearance measured exactly what it calculates to mathmatically with the compression height of the Ross pistons.

The heads were not cc'd.

I still want to degree the cam when we get it back from this latest machine shop that is looking at it.

Jeff, how do we figure the cam and it's timing's affect on the CR?

[Goose]

Yep.. aluminum rods.. Looking back I think jeez what a Dumb@ss.. but then just like in this thread, It's not the first 999 little details you check and double check.. it's the one that doesn't even occur to you ..

(But with out those occurances we wouldn't have any cool stories would we?)