Timing gear/cam help ID
Thread Starter
Pro
Joined: Nov 2004
Posts: 607
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From: North Alabama
Timing gear/cam help ID
I took the timing cover off only to uncover a mystery...the engine was physically verified to be in time but the dot on the large cam gear is at the TOP of the gear, not at the bottom across from the dot on the crank gear? has anyone ever seen this?
the marking on the end of the cam is CC 292 and what appears to be a backward 4...could it once have been an H making it a crane cam 292H grind number?
Also the marking on the large timing gear is PTC S390...anyone heard of this?
yes, I am absolutely sure the everything else lines up at TDC of the compression stroke. It is just that the dot on the large gear is at the top rather than the bottom...what gives?
the marking on the end of the cam is CC 292 and what appears to be a backward 4...could it once have been an H making it a crane cam 292H grind number?
Also the marking on the large timing gear is PTC S390...anyone heard of this?
yes, I am absolutely sure the everything else lines up at TDC of the compression stroke. It is just that the dot on the large gear is at the top rather than the bottom...what gives?
Last edited by vettepilot68; Aug 20, 2005 at 03:34 PM.
Melting Slicks
Joined: Apr 2004
Posts: 2,083
Likes: 2
From: Montreal Qc.
My 79 had both dots pointing straight up at 12 o'clock when at exactly TDC on compression stroke. These were the stock gears, had never been removed or touched.
No idea on the cam questions though.
No idea on the cam questions though.
Le Mans Master
Joined: Nov 2004
Posts: 6,128
Likes: 21
From: North Alabama
Originally Posted by vettepilot68
Thats the way this one is...just never seem it before and it is contrary to the manuals.
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
Originally Posted by vettepilot68
I took the timing cover off only to uncover a mystery...the engine was physically verified to be in time but the dot on the large cam gear is at the TOP of the gear, not at the bottom across from the dot on the crank gear? has anyone ever seen this?
the marking on the end of the cam is CC 292 and what appears to be a backward 4...could it once have been an H making it a crane cam 292H grind number?
Also the marking on the large timing gear is PTC S390...anyone heard of this?
yes, I am absolutely sure the everything else lines up at TDC of the compression stroke. It is just that the dot on the large gear is at the top rather than the bottom...what gives?
the marking on the end of the cam is CC 292 and what appears to be a backward 4...could it once have been an H making it a crane cam 292H grind number?
Also the marking on the large timing gear is PTC S390...anyone heard of this?
yes, I am absolutely sure the everything else lines up at TDC of the compression stroke. It is just that the dot on the large gear is at the top rather than the bottom...what gives?
When the dot is straight down, directly opposite the dot on the crank gear, that is TDC#6.
Le Mans Master
Joined: Mar 2004
Posts: 7,499
Likes: 1,507
From: Little Rock AR
Originally Posted by vettepilot68
huh?? thats what I have...dot on cam gear is straight up..., but I always have seen it the other way...cam gear at six oclock and crank gear at 12 oclock.. 
Keep in mind that the engine is at TDC on both #1 and #6 at the same time BUT only #6 is at TDC "Firing Position", #1 is at TDC "Exhaust Position" with the crank dot up and the cam dot down. The manual tells you to assemble it this way as an assembly aid but they never bothered to tell you it would be #6 Firing position at that point.
If you have both dots pointing UP, you are on #1 TDC "Firing Position". Both dots together when you assemble the timing gears is #6 firing position. This might sound strange but this is true.
-Mark.
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Thread Starter
Pro
Joined: Nov 2004
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From: North Alabama
Thats very interesting...and I believe all three people here that are saying the same thing, but I was just reading in the haynes manual and it said that prior to 1980 the dots should be at 12 and 6 and if it is later than 1980 they should be at 12 and 12...one of those things that makes you say hmm...
Melting Slicks
Joined: Aug 2003
Posts: 2,135
Likes: 2
From: Dayton Oh
Originally Posted by vettepilot68
Thats very interesting...and I believe all three people here that are saying the same thing, but I was just reading in the haynes manual and it said that prior to 1980 the dots should be at 12 and 6 and if it is later than 1980 they should be at 12 and 12...one of those things that makes you say hmm...
I didn't know that the car would know the difference ! 
Le Mans Master
Joined: Nov 2004
Posts: 6,128
Likes: 21
From: North Alabama
Originally Posted by marshrat99
Holy crap ! I replaced my 79's engine using a block out of an 85 Suburban. I didn't know that the car would know the difference !
I didn't know that the car would know the difference ! 
Instructor
Joined: Oct 2004
Posts: 118
Likes: 1
Your chain is on right just turn the motor over one revolution and your dots should line up on the gears, the crank turns two times for every one time of the cam, your cam should be a comp cam magnum 292, there should be more numbers on it like 12-213-3, the H on cams usually just stands for hydralic, if it has the obove number on the cam the specs are: 292 adv. duration, 501 lift, 244 duration @.050, rmp range is 2,500-6,500.
