SLANTY BLUES

-
AJ/FormS said:
I went to the Oregon site but could not find the 2106
None of those numbers can be used to calculate your Dcr
The 444/434 numbers are valve lift, probably design lift.
The 214/210 ar probably duration at .050
the 254 COULD be an advertised number, it looks about right, but it straddles the preceeding numbers so can't say which it belongs to. Maybe both I just don't know.
And without an installed centerline, you could still only guess at what number to plug in, and because it's a solid with no net installed numbers we're kindof screwed
Click to expand...
I went out and looked thru my stuff and found the cam sheet !
20181027_194531.jpg
 
AJ/FormS said:
Ya see what I mean? 254 at .020 tappet lift. Any number I wouldda given you wouldda been totally wrong.
You can't even get the ICA from the camcard!
Click to expand...


what does ICA stand for , so I can try to understand all this better.

I pulled the pistons out today, and #5 had the second ring broken and the top land looked burned up a little on the side against the cyl.
 
RAT ROD AL said:
what does ICA stand for , so I can try to understand all this better.

I pulled the pistons out today, and #5 had the second ring broken and the top land looked burned up a little on the side against the cyl.
Click to expand...
Yeah that's what I was expecting sorry. That would be detonation, probably what your travel-companion was hearing.

ICA is Intake Closing Angle. It is the supposed position of the piston in the cylinder, when the intake valve closes and therefore the position from which the chamber first starts to see compression.In your engine this is gonna be critical to know. It cannot be found on your camcard, but I'm working on estimating it.
 
AJ/FormS said:
Yeah that's what I was expecting sorry. That would be detonation, probably what your travel-companion was hearing.

ICA is Intake Closing Angle. It is the supposed position of the piston in the cylinder, when the intake valve closes and therefore the position from which the chamber first starts to see compression.In your engine this is gonna be critical to know. It cannot be found on your camcard, but I'm working on estimating it.
Click to expand...

Cleaned em up , ordered a ring set and bearings. Pistons not that bad gonna have to stick it in. This Cam spec stuff is pretty complicated chit.
 
Combustion
Chamber
63

that cannot be right,,
most stock slants have combustion chambers in the 56 to 58 cc's and you said
the head was milled .040
if the head was milled .040 I would expect to see chambers in the low 50's high 40's

also I have doubts on the .170 piston recession.
most stock slants have pistons around .180 down,
and here to again, you said the block was milled .040

either you have a stock head with oversized chambers and a block that
had a light clean up cut or you input data has errors.

how did you measure the combustion chamber cc's
how did you set the piston at Top Dead Center when you measured piston recession?
 
I did a compression check before I took it apart. 1- 4 ranged from 215 down to 175 And 5 was 50 , 6 was about 85. On a fresh rebuild I'd hope for closer readings than the span of the 1 - 4

also the 7.58 static compression ratio would never get you to the 215 to 175 cranking pressures you reported earlier.

recommend that you get the Static Compression numbers to make sense prior to working the Dynamic Compression calculations
 
Last edited:
Ok here's my best guess
the lash is spec'd at .015 VALVE lift, which back thru the rocker-arm ratio of 1.5 equals .010 TAPPET lift. So your engine will never see any duration listed at less than .010 tappet lift....... so long as the valve lash is .015 hot. Your card does not specify hot-lash.
Ok so say you lashed it hot and the .010 spec is right.Now on the card the duration from .010 is listed at 318/291 This is not advertised, this what I extracted from the card, and is what your engine will actually be seeing. So let's call it a 318/291/108 in at 104 per the card, this yields an ICA of 83*
This does not work out right in the calculator, requiring more than 13/1 Scr to achieve your pressures...... which would require a TOTAL chamber volume of 52cc @3.43x4.125. And I ain't buying that.
So bottom line is My head is against the wall. The only way I can help you is if you actually do the work of measuring the total chamber size, and also go to the trouble of establishing the ICA by finding it in the assembled engine.

But it's kindof moot because we have already established that your engine was detonating at the current pressures of 175 to 215 was it?
With this combo valve lash is critical.
And here's why; If your hot-lash was actually .030 at the valve, which is .020 tappet lift, then your intake duration falls to 254* and makes an ICA of 51*... which pulls your pressures into line at about 10/1. 10/1 seems more likely with your machining.
However, a hot-lash of .030 would be pretty noisy.

So at this point, you are looking at a pretty expensive repair bill.
Don't forget to have the rods checked for straightness,as well as the deck and head.
Also recall that I just guessed that the pressure during detonation lifted the head, and cylinder pressure escaped into the cooling system; it is a guess. If you don't pressure test the head and block, then you won't know they are good.
I would also replace the headbolts now, just in case they were overstressed. Cuz if you don't, and this happens all over again,you're gonna be saying;" why didn't you tell me?"
 
my68barracuda said:
Combustion
Chamber
63

that cannot be right,,
most stock slants have combustion chambers in the 56 to 58 cc's and you said
the head was milled .040
if the head was milled .040 I would expect to see chambers in the low 50's high 40's

also I have doubts on the .170 piston recession.
most stock slants have pistons around .180 down,
and here to again, you said the block was milled .040

either you have a stock head with oversized chambers and a block that
had a light clean up cut or you input data has errors.

how did you measure the combustion chamber cc's
how did you set the piston at Top Dead Center when you measured piston recession?
Click to expand...
Or possibly the rods are bent or short,lol.
So,Al, you seem to be up on the slanty stuff. I am not. Could you estimate what you would expect the total chamber volume might be in this combo with the info provided, and therefore make it possible to estimate the Scr; I mean just an estimate?
If you estimate the Scr, and I estimate the ICA,and RatRod Al can remember what he set the hot-lash to; that could help to get a handle on WTH happened here, and why,and what the next move should be.
 
Last edited:
AJ/FormS said:
Ok here's my best guess
the lash is spec'd at .015 VALVE lift, which back thru the rocker-arm ratio of 1.5 equals .010 TAPPET lift. So your engine will never see any duration listed at less than .010 tappet lift....... so long as the valve lash is .015 hot. Your card does not specify hot-lash.
Ok so say you lashed it hot and the .010 spec is right.Now on the card the duration from .010 is listed at 318/291 This is not advertised, this what I extracted from the card, and is what your engine will actually be seeing. So let's call it a 318/291/108 in at 104 per the card, this yields an ICA of 83*
This does not work out right in the calculator, requiring more than 13/1 Scr to achieve your pressures...... which would require a TOTAL chamber volume of 52cc @3.43x4.125. And I ain't buying that.
So bottom line is My head is against the wall. The only way I can help you is if you actually do the work of measuring the total chamber size, and also go to the trouble of establishing the ICA by finding it in the assembled engine.

But it's kindof moot because we have already established that your engine was detonating at the current pressures of 175 to 215 was it?
With this combo valve lash is critical.
And here's why; If your hot-lash was actually .030 at the valve, which is .020 tappet lift, then your intake duration falls to 254* and makes an ICA of 51*... which pulls your pressures into line at about 10/1. 10/1 seems more likely with your machining.
However, a hot-lash of .030 would be pretty noisy.

So at this point, you are looking at a pretty expensive repair bill.
Don't forget to have the rods checked for straightness,as well as the deck and head.
Also recall that I just guessed that the pressure during detonation lifted the head, and cylinder pressure escaped into the cooling system; it is a guess. If you don't pressure test the head and block, then you won't know they are good.
I would also replace the headbolts now, just in case they were overstressed. Cuz if you don't, and this happens all over again,you're gonna be saying;" why didn't you tell me?"
Click to expand...


Would it make my life a little easier If I threw the Oregan Cam in the scrap pile and put the stock one back in?
 
RAT ROD AL said:
Would it make my life a little easier If I threw the Oregan Cam in the scrap pile and put the stock one back in?
Click to expand...
NOOOOOO! that will make it worse, cuz the ICA would be waay too early, trapping even more pressure. I have the stock cam listed at 240/236/111+1, which yields an ICA of 50* about the same as the Oregon when measured at 254, which I am sure is not correct. And if it was, you would be giving up a lotta power going down 2 cam sizes for no good reason.
I tell you the truth Al, I'm having a really really hard time believing your compression tester. The data is just not syncing up.
 
Last edited:
AJ/FormS said:
NOOOOOOOOO! that will make it worse, cuz the ICA would be waaaaaaaay too early, trapping even more pressure.

I tell you the truth Al, I'm having a really really hard time believing your compression tester. The data is just not syncing up.
Click to expand...

Ya, me too. Like you said earlier , It may have still had some coolant in there. Although I spun it a while with the plugs out to try and get most all of it out prior to checking. Just as the other #s. I don't have a machine shop out in the garage. I have to use what I have at hand, so I know they are not exact #s. I asked the machine shop to take off .040 each and assumed they did so. I could put a stock head back on instead of this one ( I have 2 more). If that might help ? Thanks for racking your brain for me , I appreciate it.
 
The data is just not syncing up.

exactly,, the original poster already wasted one motor, and the data being supplied currently has to have errors in it.

I know they are not exact #s.

But the numbers need to be exact or a second engine will be wasted

Al, I think that is the original poster,,, don't take it the wrong way, but maybe you are not the right person to be checking and
assembling your engine.
There is a guy that posts on this forum for time to time,, Charlie S, that is in FL, a bit north of you. Charlie knows slants.
Charlie is a mechanic by trade, so he would need compensation, free don't pay the bills,, but you would do it once, do it right and
be able to really enjoy that nice van that you have.

just my recommendation from following these three pages of posts and trying to help
 
Last edited:
my68barracuda said:
The data is just not syncing up.

exactly,, the original posted already wasted one motor, and the data being supplied currently has to have errors in it.

I know they are not exact #s.

But the numbers need to be exact or a second engine will be wasted

Al, I think that is the original poster,,, don't take it the wrong way, but maybe you are not the right person to be checking and
assembling your engine.
There is a guy that posts on this forum for time to time,, Charlie S, that is in FL, a bit north of you. Charlie knows slants.
Charlie is a mechanic by trade, so he would need compensation, free don't pay the bills,, but you would do it once, do it right and
be able to really enjoy that nice van that you have.

just my recommendation from following these three pages of posts and trying to help
Click to expand...



I believe I have talked to the same Charlie S Before, on other matters. I have built, rebuilt, numerous engines in the past, Never had this problem . Just frustrated right know. Thanks for your help also.
 
You must log in or register to reply here.
-

Back
Top