345A cam timing

[techengnr]

I am refreshing a 345a in a ’79 sii with a thermoquad, a tf 727, 3.07 gears, and 30x9.5x15lt tires. I use this truck mostly as a parts getter and dog hauler, and to wander up the back roads, with an occasional run up the interstate.

The cylinders and crankshaft are within specification, so I am using standard bearings and rings.

I am replacing the camshaft with an isky 190156 256-hyd supercam and schneider 5510 hydraulic lifters. I had the block hot tanked and new cam bearings installed. I have checked that the bearings are properly aligned, especially #5.

I have read most of the threads here and on bp regarding cam timing, so I printed out a degree wheel and checked the new cam.

The cam card calls for (@ .050” lift) the intake to open at 11° atdc and close at 33° abdc; for the exhaust to open at 33° bbdc and close at 11° btdc. Lobe center is 112°.

I installed the cam with the marks aligned and checked lift at the #8 cylinder. These are the numbers: (@.050” lift) the intake opens at 5° atdc and closes at 28° abdc; the exhaust opens at 39° bbdc and closes at 17° btdc. Lobe center is 106° [corrected from original post]. As I understand the definition, this is advanced.

I moved the cam gear 1 tooth clockwise and have these results: (@.050” lift) the intake opens at 13° atdc and closes @36° abdc; the exhaust opens @30° bbdc and closes @ 9° btdc. Lobe center is 108°. As I understand the definition, this is retarded.

So, my choice is to run the cam advanced by 6° or retarded by 3°.

Based on my reading:

advancing the camshaft increases low speed and mid-range torque while causing high-speed power to suffer slightly.
retarding the camshaft usually provides an increase in top-end
power and consequently a slight loss in low-speed and mid-range torque.
​

I prefer to have the low speed and mid-range torque.

- is the 6° too much advance? What are the symptoms?

- does anyone have an offset key that will bring this camshaft closer to the straight up position?

- what is considered 'high speed' for this engine?

- does anyone have any other recommendations?
​

If you have read this far, thank you for your attention.

I'm not sure that I understand all of this, but I'm trying...

johnnyb

retired technical engineer, former millwright, former farm tractor mechanic.

 

[Robert Kenney]

Johnny,
if your cam degreeing is accurate, and given how you describe wanting to use your rig, you definitly want it advanced. 106-108* intake lobe cl. Your at 106* and I'd leave it there.
Compare your advanced numbers with the ones in this thread. Compare the intake closing event you measured to the stock values jesseb posted for a stock cam. You are still going to make more power on the high end and way more low end torque with the higher lift.
http://forums.IHPartsAmerica.com/gas-engine-tech/1205-timing-set-indexing-sv-4-cyl-apps.html

 

[techengnr]

Robert,
I’m comfortable with the accuracy of my numbers but sometimes I have trouble understanding what they mean. I took you lobe cl number and backtracked on mine and found my error. The lobe cl is the number that concerned me the most in my original readings.

I've attached two images showing my degree wheel and indicator setup.


Thanks for your help, I think that I’m good to go.

Johnnyb

 

[jauringer]

Hey techengnr,

just read your cam timing info and man, that just doesn't look right to me. The isky's don't have any advance ground into them off the shelf so that 6 degrees advance would all be coming from the timing gears. Directly or indirectly involved, I've never heard of one that was advanced with the marks aligned unless it had quite a bit of advance ground into it. All retarded actually. Mine isky came in @ 6.5 degrees retarded, the block in my garage right now had a comp cam that was 2 deg retarded(4 degrees advance ground in),just helped a guy out on another board just a week or so ago that was 6.5 degrees retarded....you get the picture.

Not trying to discredit your data and hey, they might be right. I'm no cam expert. It just doesn't follow what I'm used to seeing/hearing and it's no fun digging back into an engine to mess with the cam again.


Jason

 

[Robert Kenney]

hey techengnr,
the isky's don't have any advance ground into them off the shelf so that 6 degrees advance would all be coming from the timing gears.
Jason

Not entirely accurate ja. I never say never or always when speed parts are concerned. But........

Iskendarian has been grinding advance into their cams since the flat head days. I've had many opportunities to hang out with the cam father, ed and his son ron who is currently running the show. I had a lengthy conversation with him at a friends speed shop specifically about the IH stuff and the 4 popper cams. I discussed the fact that so many cams for our IH's were retarded. He and I agreed that depending on who set up the grinder they May be indexing the cam the wrong way due to the cam being gear and not chain driven. They were going to look into it. I do suspect they resolved it.

 

[jauringer]

Hey Robert, hope all is well? You're right, didn't mean to sound so definitive. I was just referring to the off the shelf IH grinds. None of them have advance ground in them. Edit: no referring to any advance/retard due to tolerences in the machine work.

The 4 I know of anyway. 190156,190125/26, 190162, and the 190170.

Jason

 

[techengnr]

Hi jason,

just read your cam timing info and man, that just doesn't look right to me.

This was my first time degreeing a camshaft. You can imagine how I felt when the numbers that I saw were so away from those on the cam card.

I decided to check the numbers on this camshaft after installing it, just on a whim, after reading the procedure for cam setup in the brochure from isky, then from several threads in this forum. It would be good practice in case I ever have to do it for ‘real’. I expected my numbers to pretty much match the data on the cam card within +/- 1 or 2 degrees. When I took my first set of numbers I was really surprised that there was so much difference from the cam card.

So I did some research, mostly here and on the bb to see if I could understand what I was seeing. I took two more sets of numbers. These agreed with the first set. So I changed the timing at the gears by moving the cam gear 1 tooth clockwise, so that the dots were 1 tooth off.

That move gave my these readings: the intake opens at 13° atdc and closes @36° abdc; the exhaust opens @30° bbdc and closes @ 9° btdc. These numbers also repeated the second time.

I moved the timing back dot to dot and rechecked again. Now the readings duplicate the original numbers: the intake opens at 5° atdc and closes at 28° abdc; the exhaust opens at 39° bbdc and closes at 17° btdc. This agrees with the data from my first set up and that’s where I left it.

I don’t know why my numbers don’t match the cam card data. I have read somewhere in the last few days that it was not unusual for the keyway in the crankshaft to be off a little, from the factory. That might be hearsay or urban legend or whatever.

As I said before, I’m still trying to understand what all the numbers mean.

I thought about reinstalling the old cam to see how it looked with a degree wheel, but at this point I had already spent 3 days on this one lesson and needed to move on. On the next tear down, I’ll be a little more diligent about checking and recording clearances and settings as I take it apart.

I appreciate your comments and am interested in seeing any more ideas you have on this.

Johnnyb

 

[Robert Kenney]

I would suggest checking another cylinder. I always use #1. It will require a full reset and then if you get the same numbers its safe to say you're good.

 

[jauringer]

hi jason,

this was my first time degree'ing a camshaft. You can imagine how I felt when the numbers that I saw were so away from those on the cam card.

Morning techengnr. Yep, I remember feeling the same way @ 6.5 deg retarded. I did the same thing you're doing here, "ask Robert".

I decided to check the numbers on this camshaft after installing it, just on a whim, after reading the procedure for cam setup in the brochure from isky, then from several threads in this forum. It would be good practice in case I ever have to do it for ‘real’. I expected my numbers to pretty much match the data on the cam card within +/- 1 or 2 degrees. When I took my first set of numbers I was really surprised that there was so much difference from the cam card.

So I did some research, mostly here and on the bb to see if I could understand what I was seeing. I took two more sets of numbers. These agreed with the first set. So I changed the timing at the gears by moving the cam gear 1 tooth clockwise, so that the dots were 1 tooth off.

That move gave my these readings: the intake opens at 13° atdc and closes @36° abdc; the exhaust opens @30° bbdc and closes @ 9° btdc. These numbers also repeated the second time.

I moved the timing back dot to dot and rechecked again. Now the readings duplicate the original numbers: the intake opens at 5° atdc and closes at 28° abdc; the exhaust opens at 39° bbdc and closes at 17° btdc. This agrees with the data from my first set up and that’s where I left it.

I would have probably done the same thing here. The numbers all correlate and were repeatable. Roberts suggestion is a good one. If they follow suite from here it sounds like you've done everything you can to confirm those numbers. Great example why it's so important to degree a cam!

I appreciate your comments and am interested in seeing any more ideas you have on this.

Johnnyb

Again, the intention wasn't to discredit your numbers and send you into a frenzy. Just better to be safe than sorry. Assuming the the numbers match up on this last test, it sounds like it will end up working out pretty nice, being right in Robert's recommended 106-108 intake centerline.

Jason

 

[techengnr]

I would suggest checking another cylinder. I always use #1. It will require a full reset and then if you get the same numbers its safe to say you're good.

I checked #1, and for just for grins, #5 too. The numbers are all the same, so I guess it is all good.

again, the intention wasn't to discredit your numbers and send you into a frenzy.

Better they be discredited now than later, so that if there is a problem it can be fixed. I learned early on that if the readings don’t match expectations, then the first step is to recheck the readings. And then again just to be sure. Then you can start looking for the discrepancy.

Sometimes it takes a frenzy for them to know that I’m still kicking.

johnnyb