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Comp cams

Started by _Bluejinx202_ , Oct 19 2012 04:01 AM

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114 replies to this topic

#76 _oldjohnno_

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Posted 05 August 2013 - 08:57 PM

Can you recheck at 0.050" tappet lift, and post the numbers in BTDC/ABDC format?

What lobes are they?

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#77 _Bluejinx202_

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Posted 05 August 2013 - 09:32 PM

Int. opens 19 btdc@50
Closes 50dabdc @50

Ex opens 135 datdc @50
Closes 27 datdc @50

Lobes are 6302/6303-110

I'm not sure if I've put what you have asked for here

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#78 _oldjohnno_

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Posted 05 August 2013 - 10:01 PM

There seems to be a bit of a discrepancy with either the cam or your measurements. The intake lobe is only out by a degree of duration but the exhaust is out by two. As well the LSA works out to about 102 and the ICL is retarded. But before you get too excited check with Comp on the lobe centreline location - it can turn out to be different to the "normally" calculated position with these assymetric lobes. I wouldn't be surprised if this is the case here. What are the figures on the cam card for 0.050"?

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#79 _Bluejinx202_

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Posted 05 August 2013 - 10:19 PM

Looking at the card now- it says

Int, @50

15 btdc
55abdc

Ex, @50

57 bbdc
17 atdc

I have

19/50 in
45/27ex

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#80 _oldjohnno_

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Posted 05 August 2013 - 10:53 PM

The LSA looks to be closer than it should be. Time to talk to Comp about returning it.

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#81 _Bluejinx202_

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Posted 30 August 2014 - 01:54 PM

Just started to take engine apart with a suspected blown head gasket after dropping cyl 6 last week. Got the rocker cover off to find no rocker movement on number six, took out those two lifters and the cam isn't turning 1-5 is fine, looks like I have a snapped camshaft

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#82 warrenm

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Posted 31 August 2014 - 06:39 AM

Ouch.

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#83 _Bluejinx202_

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Posted 02 September 2014 - 08:00 AM

Got the engine apart last night, pulled out the two pieces of camshaft. It is a clean break, I can sit the two pieces together and you would struggle to see where it seperated the crack is that clean. The cam appears to be broken in two pieces only, no fragments. There is no evidence of any contact with anything that it shouldn't be (ie, conrod that I thought it was going to be). All bearings and bearing surfaces seem clean and of normal colour and shape. The end bearing that the broken piece was resting is not seized and seems still fine. Should I slide a new cam in and keep going? I feel like I need a reason this happened to be confident it doesn't happen again....

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#84 greens nice

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Posted 02 September 2014 - 11:29 AM

Something is going on, has it broken right of the edge of the machining undercut?
I'm assuming you saw my broken comp cam? But I put mine down to running 400lbs open pressure, maybe not.
I've got two more here that I'll crack test before they go Into service.
I have one still running with .392" lobe lift and 370lbs though.

Take some pics and send it to comp.

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#85 EunUCh

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Posted 02 September 2014 - 11:54 AM

Has been a couple of broken cams lately,bit hard to tell what happened,in my case it was a regrind and after a close look at the ramps it looks

like what happened was the lifter dug itself into the ramp and decided to pull things up a bit,after blaming the oil and 350lb open springs it looks like because of the grind i got it went through the hard facing and was not re-hardened,this made sense to me because most lobes were worn and the worst one was 1mm worn.

Edited by EunUCh, 02 September 2014 - 11:54 AM.

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#86 _Bluejinx202_

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Posted 02 September 2014 - 12:52 PM

529E46E5-1BAD-4898-BAE0-B314580E951E_1.j

Couple of other things to mention in light of the above posts.

The spring pressure is 125lb/300lb there are straight cut gears involved. I don't like them and only put them in because it was the only set I had with adjustable keyway. The retainer is broken, I didn't think much of it as one side was still bolted to the block and thought it might have broke when I undid the bolt.
This might be a sign that helical gears should be preferable in these engines.

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#87 _Bluejinx202_

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Posted 02 September 2014 - 12:56 PM

Something is going on, has it broken right of the edge of the machining undercut?
I'm assuming you saw my broken comp cam? But I put mine down to running 400lbs open pressure, maybe not.
I've got two more here that I'll crack test before they go Into service.
I have one still running with .392" lobe lift and 370lbs though.

Take some pics and send it to comp.

I haven't seen you're broken cam. It has broken where you describe. If you see the pic above, the first lobe above the crack is the intake of cyl6

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#88 greens nice

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Posted 02 September 2014 - 05:33 PM

But I don't get why it's on no. 6 on both cams.
I would have thought it would be most stressed right behind the timing gear, before now I've only heard of them breaking there.

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#89 EunUCh

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Posted 02 September 2014 - 06:30 PM

Could be wrong, but by the looks of the wasting away it looks like a regrind,the odd thing about where it broke?,when the horrendous

starfire cam broke it was at the back as well,#4 intake?

The other thing i was wondering without drifting too far off topic is do we really need all that spring pressure?

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#90 _Bluejinx202_

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Posted 02 September 2014 - 06:45 PM

Has anyone got another holden six comp cam to look at? This picture shows my old cam which appears much stronger than the comp.
Note the same core number

Edited by Bluejinx202, 02 September 2014 - 06:46 PM.

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#91 _Bomber Watson_

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Posted 02 September 2014 - 07:10 PM

Kev has my brand spankers new one in his hot little hands atm, i'll see if he can get a pick of it to compare.

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#92 _oldjohnno_

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Posted 02 September 2014 - 08:21 PM

The undercut is normal for highish lobe lifts - without them the grinding wheel hits the shaft on the base circle. Lower lift lobes don't need it though. The most likely cause of the break is insufficient fillet between the machined and unmachined sections. A larger fillet - or simply just machining the whole length of shaft between the lobes - probably would have saved it. Keep in mind that Holden (and Chev) sixes put unusual stresses on the shaft because there is such a long distance between the journals. Lay one alongside a SBC cam and you'll see what I mean. For big lifts, heavy springs and prolonged use it might pay to use a billet steel core, once you've done your testing on the cheap cast cores.

Heres another comp with moderate (0.56") lift.

Edited by oldjohnno, 02 September 2014 - 08:24 PM.

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#93 _Bomber Watson_

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Posted 02 September 2014 - 08:37 PM

I see what you did there.

Why such a good cam manufacturer makes such a mistake, of just hard cutting edges, is beyond me.

Once Kev hands mine over to me in a cople of weeks i might look at putting it in a lathe at work and taking the whole thing back to the size of the undercuts....Or just run it....Hmmm, decisions decisions.

Cheers.

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#94 N/A-PWR

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Posted 02 September 2014 - 08:40 PM

Great Information Oldjohnno,

I haven't seen one of those Cam's before, with the shaft relief,

but yes about the edges having some sort of radius instead of a machined sharp corner,

as this is to prevent cracking.

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#95 greens nice

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Posted 02 September 2014 - 08:58 PM

So it's got around .370 lobe lift john?
After this amount of carnage something has to be done about it.

Eunuch, they were xtq&xtx lobes, 140 seat pressure and 370 open and the valvetrain went nuts after 7100
.900 core diameter probably isn't much of a problem in a shorter v8.

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#96 _Bomber Watson_

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Posted 02 September 2014 - 09:00 PM

Yeah, sure, something ahs to be done about it AFTER you get my cam in........Demand a recall, i dont need mine instantly

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#97 greens nice

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Posted 02 September 2014 - 09:09 PM

Hey I ordered it before any of these problems arose, you know I would make it right......

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#98 _Bomber Watson_

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Posted 02 September 2014 - 09:13 PM

I know i know

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#99 _oldjohnno_

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Posted 02 September 2014 - 09:16 PM

So it's got around .370 lobe lift john?
After this amount of carnage something has to be done about it.

Eunuch, they were xtq&xtx lobes, 140 seat pressure and 370 open and the valvetrain went nuts after 7100
.900 core diameter probably isn't much of a problem in a shorter v8.

Something like that, I don't remember exactly...

I wouldn't get over-excited, and I don't think it necessarily means that every undercut cam for a Holden is going to break. I wouldn't worry too much at all for a street and strip or a drag car, but for something that does prolonged high rpms (like a boat perhaps?) it might pay to check it out.

Like most aftermarket parts these things are made to a price, and I really don't think you can complain when the occasional cast-core cam breaks when it's run with heavy springs and a few revs. It's rare to find a performance part that's 100% ready to use straight from the box.