COLLAPSED PISTON

John Strenk

1980_Cj7 wrote
Here's the pics as promised. The first pic is No. 1 on the left and No. 3 on the right. The second pic is No. 5 on the left and No. 7 on the right. All showing the top (intake side) of the pistons.

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Just a silly question, Did you have this block line (or "Align") bored or honed? What if the crank was off a little bit front to back. ? If this block has never been touched since it was first manufactured things could of "shifted" a bit.

Also George I alway use a torque plate with those clearances but I'm not a big block builder. It's been years since I even owned a V8. 🙂

jeepsr4ever

Looks to me like the bores arent correct our you overheated the engine quite a bit.

1980_Cj7

Oops, missed a couple questions above. Ross hasn't offered to do anything for us. Nor would I expect them to if it wasn't their fault. We haven't really pinned down what caused this yet. Haven't decided on replacement pistons yet. The way I understand it, forged are more touchy than cast or hyper, like having to be warmed up for one thing. Thinking about the Keith Black 354's hypers that give the 9.5 CR, if I can be assured they will run on pump gas. I like the support KB has been giving us, even though we didn't buy their pistons, and all the great tech they have on their site. Their pistons have the proper 1.51 compression height to give the 0 deck clearance too. Need to see how the bores clean up first and decide what to do from there. MC, the engine wasn't over heated. Highest it ever saw was 225 maybe. We put a new oil filled mechanical Autometer temperature gauge in before we ever fired it up so we could keep a close eye on the temp. Put an Autometer oil pressure gauge in too. Those stock CJ gauges leave a lot to be desired. John, don't know how the engine was bored, other than the fact that a honing plate was not used. I asked about that after we had this problem. It was still stock when we got it, and not being engine builders, but at least knowing what we didn't know, we took it to a builder and just told him to do what needed done. We did have it balanced. I did notice when checking for burrs at the bottom of the bores, like someone posted about, that there is a step in the bottom edge of the cylinder walls. Hard to describe. Wish I could draw a picture. The interior bore is straight and smooth, but as you turn the corner at the bottom of the bore, like to feel the thickness of the cylinder wall, there is a distinct step there. Does this make sense? Has anybody else experienced this and is it normal?

John Strenk

I was talking about how the crank sits in the engine.

Read about align bore crankshaft:
http://www.eddiesvalvegrinding.com/boring-honing.htm

1980_Cj7

John Strenk wrote
I was talking about how the crank sits in the engine.

Read about align bore crankshaft:
http://www.eddiesvalvegrinding.com/boring-honing.htm

Yes, I understand. I just wanted to add something else I discovered to this thread in case it is pertinent.

AMX69PHATTY

Nominal Compression calculations for the KB 354 Pistons.
Shortened the Connecting Rod by .003 to represent re-conditioning.

Here's the calculations using the stock Connecting Rod Length

1980_Cj7

Thanks. Now, is anybody running that kind of compression ratio on an engine similar to ours and will it run on pump gas without pinging? Still waiting to hear back from the machine shop.

Blown7

1980_Cj7 wrote
Jeff, how do we figure the cam and it's timing's affect on the CR?

First let me say I'm no cam expert, cam theory is even debated by the experts. Find yourself a expert and let them figure it out, but heres a elementary link to explain whats going on.
http://e30m3performance.com/myths/more_myths1/comp_ratio/comp_ratio2.htm

Then move into a more detailed explaination
http://www.empirenet.com/pkelley2/DynamicCR.html

And here is a calculator
http://www.kb-silvolite.com/calc.php?action=comp

Then you have to consider the cam timing to engine (with the timing wheel and the dial indicators) and where and what keyways you use on the cam timing gear to advance or retard the cam. The problem your going to get on a forum like this or anyother for that matter is your going to get a engine built by a commitee. You have to figure WHAT YOU WANT then what you want for performance, and then your going to have to compromise to get it. Whether you want low end grunt or high end power.

Unless you build a blower engine, then you can have it all :lo1l: BTW I can change dynamic compression ratio just by changing blower pulleys.

Jeff

1980_Cj7

Thanks again Jeff. I ran the calculations with our numbers and here's what I got. I tried to cut and paste from the calculator, but it only pasted part of the numbers. Seems like it left out the numbers I filled in, and only pasted the calculated numbers. Anyhow, at least is shows the bottom line, the compression ratios. The static is very close to Ross's published 9.8. The dynamic with our cam came out to 9.2. Seems like that should have run on pump gas. I still suspect something is awry with the timing. Can't wait to get it back from the machine shop and check the cam timing. Fuzz has a degree wheel so we're gonna visit him and together see what we can find.

Again, our intent wasn't to build anything radical, but to just cheat a little more power out of the engine since we had to buy new pistons anyhow.

ENTER YOUR DATA CALCULATED DATA
Cylinder Head Volume (cc) Cylinder Head Vol
(cubic in.) 03.538
Piston Head Volume (cc) Piston Head Vol
(cubic in.) 01.403
Gasket Thickness (in.) Swept Volume
(cubic in.) 50.863
Gasket Bore (in.) T.D.C. Volume
(cubic in.) 05.820
Cylinder Bore Diameter (in.) Gasket Volume
(cubic in.) 00.644
Deck Clearance (in.)
Note: Neg. nubmer above deck, Pos. number below deck Deck Volume
(cubic in.) 00.235
Stroke (in.) STATIC COMPRESSION RATIO 09.739

OPTIONAL DATA
Rod Length (in.) Adjusted Stroke (in.) 03.456
Intake Closing Point (degrees)
ABDC @ 0.050 lift plus 15 degrees DYNAMIC EFFECTIVE COMPRESSION RATIO 09.207

Luv your blown engine! (Hey guys, I think we just found somebody with more power (read "money") than Fuzz. :mrgreen: )

AMX69PHATTY

Here's the calculations using nominal values for an engine I had in my
'69 AMX for many years and I had no problems with pinging on pump gas.
It's out of the car now cause I spun a rod bearing taking it to ₇₀₀₀ rpms
and it was not built for that and I didn't have the oil line in the lifter valley.

The hydraulic Cam was a stock unit reground by Chet Herbert.
Only have limited data on it, .512/.529 lift, 280/295 adveritsed, 110 centers.
Used Crane Hi-Intensity semi-anti-pumpup Lifters.
Cast Sealed Power Pistons, dished tops with 29cc, .020 shorter than stock.
Manufacturers of stock type replacement pistons make them .020 shorter
to allow for Cylinder Head and Block deck milling and to still maintain stock CR.
I have a '69 343 block with the shorter deck hieght, 9.175
Stock 343 4V had flat top pistons that were .060 down in the hole.
The Sealed Power units were .080 down in the hole with a huge dish.
This was "made up" by using a 304/360 crank in the 343 block.
There is a .160 stroke difference between a 343, 3.28, and a 304/360 crank, 3.44.
So the 304/360 crank pushed the pistons up .080 further to 0.000 deck and
with the dish in the SP Pistons compression came out at 9.5 thereabouts.
Recurved Distrubutor, 26 deg mechanical, 10 deg initial, 36 total at 3500.

I did not have any problems pinging running pump gas in this motor.
This motor made about 400 HP at the flywheel, 325 HP at the tires.
It chassis dyno'd 285 HP at tires before swapping on milled ported heads.
325 Tire HP calculated using the cars wieght and 1/4 mile MPH from the track.

I am currently working on getting this motor back together with more CR.
This time I offset ground the 304 crank .010 for a 3.46 stroke
and the pistons stick out of the block .007-.010, and CR is around 10:1.
I am also advancing the same cam 4 crank degrees where before it was strait up.
This closes the Intake valve sooner and creates more effective CR.

Per the SilvoLite page compression calculator.
I'm surprised my Dynamic compression was less than 8.0:1
That goes along with me not having detonation problems, like 82Waggy mentions below.

82Waggy

Dynamic compression ratios in excess of 8:1 are typically considered too high to run on pump gas, and you generally want less if you are going to be towing or lugging the engine to prevent detonation. If you are planning on using the KB 354 28cc dish pistons, just do the math and try to get as close to zero deck as you can within a couple out or three - five thousandths down (after decking the block square, taking off as little as possible) . With an .045 thick head gasket (4.275bore) you will have a good quench distance (.043 - .050 is good for a steel rod 401). You then should probably consider polishing out the head chambers to around 62- 65cc to get the static compression ration down as close to 9 - 9.25:1 as you can - polishing the chambers (smooth surfaces) also helps reduce potential detonation. With proper bore clearance you should be golden. Oh, and go ahead a put that valley line in. So long as it does not leak it won't actually hurt anything. #-o

AMX69PHATTY

I added an image of the SilvoLite page calculations for my 365 engine to my previous post.
My dynamic compression was less than 8.0:1
so that goes along with what 82Waggy had to say about detonation.

Here is the specs I fould for what I believe is your Clevite Cam
and the results of the SilvoLite Compression Calculator for your 401.
It indicates a dynamic compression of 8.63:1.
I wonder if this much dynamic compression may have been causing detonation.
Wonder if detonation may have something to do with the piston scuffing ??
Let me know if any of the values are incorrect.
This is interesting since I'm currently building an engine myself.

Blown7

Awww AMX69PHATTY your doin all his homework for him, I was hoping 1980CJ7 would figure this out all on his own. Yes the numbers sound about right, a recipe for a internal engine nuclear bomb. Unless you run high octane fuel or alcohol. Typically the cams with over 112 degrees are some pretty finiky cams. This is the reason why a engine is absolutely built around a cam as the FIRST item. Pistons being one of the last as the pistons can be massaged to work. Thats why I like these new tuner kids you hang with them a while and find they are running damn near 20 to 1 static compression pistons in those little Hondas and yet running pump gas. Jeff

82Waggy

I went with a Crower grind myself, with an intake closing point closer to 60 ABDC. You have to watch cam selection as many are designed to improve dynamic compression ration on low static CR stock engines. The following static CR recommendations were clipped from an article on the KB Site. Note that these are for "regular" grade gas. You might get away with another .25 or so in CR if running Premium gas. ----- The following compression guide should be considered realistic for sea level operation. Cam timing and special applications can move the recommendations around some, but in most cases the following recommendations work. PUMP GAS (regular) 8.5:1-Non-quench 2 valve head road use standard sedan, without knock sensor. 8.5:1- Quench head engine for tow service, motor home and truck with torque cam. 9.0:1- Street engine with proper .040" quench, 200¬? @ .050" lift cam, iron head, sea level operation. 9.5:1- Same as 9:1 except aluminum head used. Light vehicle and no towing. 10:1- Used and built as the 9.5:1 engine with more than 220¬? @ .050" lift cam. 10:1- 4" and smaller bore, high RPM cam, cold plugs, good fuel distribution, full power limited to 30 seconds W.O.T.

1980_Cj7

Oops, I forgot to add the 15 degrees to the intake closing point when I did the calculations. Wasn't stock compression ratio for the 401 8.5:1? Is that static CR that they list? If so, I wonder what the dynamic CR is on a stock 401.

Blown7

For comparison, here are the stock AMC V8 cam specs taken from my 1977 technical service manual:

'74-78 304
'74-'74-79 360 ' 74-78 401
Lobe lift .266" .286"
Valve lift (1.6x) .426" .458"
Intake valve opens 14.75* BTDC 25.57* BTDC
Intake valve closes 68.75* ABDC 90.75* ABDC
Exhaust valve opens 56.75* BBDC 80.80* BBDC
Exhaust valve closes 26.75* ATDC 42.75* ATDC
Valve overlap 41.50* 68.32*
Intake duration (adv) 263.50* 296.32*
Exhaust duration (adv) 263.50* 303.55*

Lobe separation angle
(computed by me, error-prone) 111* 115.8*

Stolen from another site, I don't have my TSM at home
http://www.jedi.com/obiwan/jeep/wagoneer/401/cam.html
Yes stock SCR is 8.5 to 1
Jeff

82Waggy

Yes, the CR recommendations listed by KB are static ratios.

1980_Cj7

Jeff, I'm trying to compare the stock cam to our cam, and also use the calculator to see what the dynamic CR is on the stock engine. Why are there two sets of numbers after each event, like intake opening 14.75* and 25.57*?

Blown7

1980_Cj7 wrote
Jeff, I'm trying to compare the stock cam to our cam, and also use the calculator to see what the dynamic CR is on the stock engine. Why are there two sets of numbers after each event, like intake opening 14.75* and 25.57*?

First number is 304/360 engines and the second is the 401, the cut and paste didn't work well with my computer if you click on the hyperlink the box comes up correctly.
Jeff

AMX69PHATTY

WOW ! - 6.3 Dynamic Compression !?!?!?!? for a stock 401 :shock:
did I get sumthin' wrong ???? - fixed intake closing angle - ( thanks 82Waggy )

For a stock 8.5:1 AMC 401 camshaft I assumed a 30.75* Intake valve closing ramp,
subtracted from 90.75* in the AMC Manual ends up as 60* ABDC @ .050 lift.
The Badger Piston dish spec I have of .300 is pretty dang gone deep !
I guessed at the stock Piston Volume of 40cc's to get the 8.5 Static CR.
Unbelievable stock Dynamic CR is only 6.3:1 !!!!
If this was common, no wonder smog motors where so dead.
I assumed you started with a post '72 8.5:1 CR 401 Motor ?
I have a stock '73 401 sittin' in my garage waitn' for the next time.
Crank turms twice per one Cam revolution, Cam angles are in crank degrees.
Cam spec angles designate the valve events and corresponding crank position.
ATDC = After Top Dead Center
BTDC = Before Top Dead Center
ABDC = After Btm Dead Center
BBDC = Before Btm Dead Center

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