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#1
09-10-2023, 07:26 PM
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cam timing
In the process of rebuilding the 400 out of my son's 69 Bird. The cam is a hydraulic roller with duration of 248/254 at .050. Just pulled the cam card to verify the intake centerline which is 105*. That # represents 4* advance ground in, and it did degree in at that number 14 years ago when the cam was new. Now when I degree the cam I am seeing 110* intake centerline. IIRC the rational for grinding in a certain amount of advance is to allow for the inevitable timing chain/sprocket wear, which in my case has certainly happened. Question is whether I leave it alone or use one of the other key ways on the Cloyes crank sprocket to get back to the 105* centerline or maybe shoot for something in between. Any thoughts?
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69 Bird w/1970 400 block(409 cubes), #64 heads, hyd. roller, Q-jet by Jeff E., original interior, ps, pdb, th350, and 3.73 gears. Pump gas, street driven muscle. 3800 lbs. race weight. Best, 11.39 @118, my son's car. 79 T/A w/463, Scat crank, Eagle rods, Icon pistons, Lunati solid roller, 262/270, KRE 325 heads, Northwind intake, QF950 carb, full interior, ps, pdb, th350, and 3.73 gears. Pump gas, 3650 lbs. race weight. 10.68 @ 126 so far... no tuning yet. |
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#2
09-11-2023, 11:33 AM
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Well since you race it you get to decide by your time slips.
If you want to keep the mph where it is then leave it as is, but back at 105 might do you better interms of ET.
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#3
09-11-2023, 07:24 PM
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They don’t seem to ever stop stretching.
I would just put a new chain on it, or complete new timing set, and put the cam timing back where you want it. Having a loose chain with a lot of slack isn’t very ideal. |
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#4
09-11-2023, 08:15 PM
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Roger that. I was leaning toward a new chain or complete set.
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69 Bird w/1970 400 block(409 cubes), #64 heads, hyd. roller, Q-jet by Jeff E., original interior, ps, pdb, th350, and 3.73 gears. Pump gas, street driven muscle. 3800 lbs. race weight. Best, 11.39 @118, my son's car. 79 T/A w/463, Scat crank, Eagle rods, Icon pistons, Lunati solid roller, 262/270, KRE 325 heads, Northwind intake, QF950 carb, full interior, ps, pdb, th350, and 3.73 gears. Pump gas, 3650 lbs. race weight. 10.68 @ 126 so far... no tuning yet. |
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#5
09-12-2023, 08:26 AM
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Think there was guidance in a Thread to use the stock-style chain from a certain MFGR (forget the mfgr), and a few good Double-Bicycle Rollers (forget the mfgrs). Bet CLIFF knows.
I have had good results with the double bicycle chains that i bought (cheapo) and have seen sloppy results in a few engines that got torn down. Original Factory stock though probably the worst as the slack slapps the Timing cover. |
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#6
09-28-2023, 05:39 PM
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The main problem with the Pontiac factory timing chains was the nylon outer gear that wore out and chunks coming off and the chain jumping timing. They used them for many years because supposedly they were quieter. They eventually stopped using them I don't know what year they started using the all metal cam gears.
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Tim Corcoran |
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