: Cam journal caps broke



IXSLR8
08-24-11, 05:21 PM
OK. Iíve got a question regarding early northstar cam journal caps.

I've put about 2000 miles on a low mileage 1996 engine and reground 272 cams and started getting some lifter noise.

I pulled the motor to inspect what was going on today and found that the exhaust cam, on the left hand side, had two cam journal caps broken (on the bottom side of the cap). Those two cam journals must have had loose bolts in them and I think that they worked themselves loose and eventually broke with the cam slamming them. That is what was making what I thought was lifter noise.

So Northstar friends, I was just wondering what would cause the cam journal caps to break? Could it be the harder springs and reground cams from CHRF making more push against the journals? ...My head shop not tightening all the cam cap bolts correctly when they checked and installed the 272 cams?

Iím going to have to find two journal caps I guess. I kinda think that it is not good to use new caps on my used head since they may have variances since they were not line bored together. Also, what do you think about using blue Locktite so the bolts canít back out, get loose and break?

IXSLR8
08-25-11, 01:01 AM
I checked the other head to see if there were any issues with it.

I found that the exhaust cam had random loose bolts that were only hand tight at best. What's with that? The intake cams were fine on both sides but the exhaust cams had loose bolts.

Any thoughts?

Submariner409
08-25-11, 10:26 AM
Last line, second post: Someone doesn't know how to build an engine: Cam bearing caps don't just come loose - what about the other few million or so Northstars out there ? Those cam cap bolts have a specific torque sequence - it's in each year's service manual.

The heads and cam journals were probably not designed for high load springs - the engine is already spec'd to operate at 6,500 rpm - what were you winding it to that it needed heavier springs in the first place ??? (...........and the "reground 272" cams are not the answer.) Stock VIN 9 cams are already very close to a "272" at .006 (advertising hype) lift measurement. What are these at the real measurement lift of .050" ?

Go back a year or so in these threads and find the 8 cam specs cards posted by AJXTCMAN. You'll find that the original GM cams are pretty decent, duration-wise, as is while the CHRF cams are nothing special to write home about, either. For the stoplight derby guys, it's too bad that CompCams won't grind a set of their Thumper cams for these engines - true bling.

IXSLR8
08-27-11, 12:36 PM
Yes, I think your right. someone got a phone call and forgot to tighten them to specs at the head shop.

According to my service manual for 1996, the torque values are 106 inch pounds.

Yes, I was made aware of the cams by AJ as far as the specs go. They netted me an extra 20 HP on the dyno. Not worth the expense for the gain in my opinion.

The springs were put in to raise the rev if I wanted it at a future date with mods. I've only revved the engine up to 6500 and babied the engine pretty much. That's why I was shocked to find lifter noise on this low mileage 50K engine. When I opened it up, I found broken cam caps on the exhaust side and random loose bolts on the exhuast side of the other head. I think that's odd.

I'm going to retorque with blue locktite on each bolt and mark each cap when they are done.

I know this is sacreligious (because each head is line-bored with their respective caps) but I pulled some cam caps from a 4.0 Aurora. I torqued each one with plastigage on the cam journals. I did it on three areas of the cam caps to determine if they were out of round, offset or had enough room for lubrication. The were surprisingly accurate. So, I'm using them. I guess I'll see if I have more trouble on my cams in the future with the Aurora cam caps.

Submariner409
08-27-11, 03:44 PM
Nope - no trouble with caps that gauge correctly.

If the CHRF regrinds (no other work) gave a 20 hp gain at hp peak, that's nothing to sneeze at. With that running timing spec and your dyno results, I'd guess the cams come in at 4,000 and up. What did they do at low rpm normal starts ?? Any bog or hesitation ?? [1996 - was anything done to fuel mixture in this {tuneable} PCM ?] (This is interesting........)

IXSLR8
08-31-11, 03:31 PM
Well, I went back and retorqued each bolt on all the cams and used blue locktite on each bolt after cleaning. I had one bolt break off when removing it. I wasn't hard on it either. It simply broke. I decided to use the cap as a guide and transfer punch a divit for drilling. Surprisingly the 10.9 graded steel was easy to drill with a cobalt drill bit.

The problem was getting out the metal threads as some of the bolts had corroded with the aluminum and wouldn't come out easy. The more I worked that hole, the worse it became...to the point that I thought I should just get another head(the proper thing to do since they are line bored together). I ended up getting most of it out with tools I had to make and old dental tools. For the rest of the debris, I just drove the matter to the bottom of the hole. I used a stud instead of a bolt in that hole.

The Aurora cam caps are working fine. So, I'm having spirited fun again. Put 120 miles on it so far and not a lick of lifter noise.

The cams are kinda weird on the low end. I find them to almost hesitate, as you describe, like a soft miss or something at low rpms and idle. When your into it with your foot, that's all gone and it pulls strong all the way up to 6500rpms. Since I'm using the LS1 PCM, I'm not personally tuning it. I did have the dyno folks working on the LS1 tune for 12+ hours working out the bugs. Its drivable but It still has a random stall at 205-210 degrees and higher occasionally. I don't like that at all.

After doing this, I would not recommend the 272 CHRF cams with a stock Cadillac PCM for an early 94-99 Caddy...or an LS1 PCM. Perhaps another more Cadillac-like cam may work by a different manufacturer. I understand that the CHRF cams have the centerline set-up differently(I don't know what that means). According to Howell engine developments, you can use up to a 272 cam with out ill effects on a stock 1995 Cadillac PCM #16196402. But, I don't know what brand cam they were talking about when I talked with them two years ago.

Anyway, I really like the Northstar but it seems to work best in a stock configuration. That's my take at the moment with out spending thousands of dollars.

Here's my first dyno run to see what the Shelby/LS1 Tune on the Northstar is doing: http://s423.photobucket.com/albums/pp311/I-XSLR8/?action=view&current=DynoShelbyNorthstar025.jpg
I don't think this is very impressive for 272 cams and headers and the Shelby program.

Submariner409
08-31-11, 05:49 PM
I understand that the CHRF cams have the centerline set-up differently(I don't know what that means).

The cam center line (think of 12:00 on a clock) is the number of degrees before/after TDC calculated in the opening/closing events of a particular grind. It's the "12 o'clock" relationship of the intake and exhaust durations. Ok, all well and good. If you get a set of cam gears that have adjustments for +4, 0, and -4 degrees timing in relation to crank rotation, then you can do three things: Advance the cam 4 degrees - the power curve comes in earlier in rpm. Set the cam to design - 0 - degrees and the cam performs about as advertised. Set the cam timing to -4 degrees and the power curve moves up in the rpm curve.

The kicker with the Northstar is that there is no way to advance/retard cam timing unless you slip a timing chain tooth one way or the other - and that's too many cam degrees to do any fine tuning. So, I would assume that there are two cam regrind options: move the curve one way or the other a few degrees, BUT, regrinding a cam removes lobe lift, so you have to be damn careful how much (grind) and how many (degrees) you move the lobe profile.

Get into any of the major cam manufacturers sites and find a timing card for any old cam. It gives you a slew of timing events. Just like a watch dial, if you rotate the cam card clockwise you retard the cam (timing); conversely, rotate the card counterclockwise, you advance the cam (timing). (EDIT: This CW/CCW offset depends on the engine rotation itself)

I hate to say this, but the dyno graphs appear to indicate that, compared to a stock engine, you actually lost power. Will you have before and after strip timeslips to compare ? If the graphs are engine crankshaft power, one thing; power on the pavement, another.

IXSLR8
08-31-11, 11:10 PM
Thanks for the Education Sub. I appreciate that a lot.

The dyno numbers were HP and Torque at the rear wheels.

I bet I would not have the tuning/Performance issues using stock VIN 9 cams. I guess I need to look for a good set of VIN 9 cams.

I imagine you could modify the cam sprockets and make them adjustable where they mount to the cams to allow for some degree + or - movement.

Submariner409
09-01-11, 08:50 AM
No problem - that explanation left out a lot and is pretty simplistic. If you really want to go freako on cam design and how they can be changed to make/lose power, get into the CompCams, Edelbrock, Lunati, Mondello, or Engle sites.

IXSLR8
09-10-11, 09:10 PM
Still no issues after 800 miles. Not a lick of lifter noise. I like that!