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Cam grind and this sucks
https://slantsix.org/forum/viewtopic.php?t=6725		 Page 1 of 1
Author:  customsportsman [ Fri Aug 29, 2003 6:20 am ]
Post subject:  Cam grind and this sucks
Fellas,
DD asked what cam I used that I was so happy with. The cam was a crane 720771. Works great when the engine WAS running.

However last night, I bent 2 push rods. One popped off and I found the #1 intake valve partially stuck open. It popped free, but I wonder if the machine shop who did my head work didn't check the stem to guide clearance. Also #1 exhaust was bent, but still on. Engine runs fine, compression is still good so no valves were mashed into the piston, but I wonder what caused this in the first place? Geez, now I don't trust this motor AGAIN!! Sucks doesn't it?? Anybody else ever have this happen to them?
Author:  Tom Drake [ Fri Aug 29, 2003 8:09 am ]
Post subject: 
What kind of pushrods were they? Stock or aftermarket?
Author:  relic-lover [ Fri Aug 29, 2003 8:14 am ]
Post subject:  Bent pushrods
I had 2 pushrods bend in our 63 Dart in a completely stock engine.
Have never got a "for sure" answer why it happened. I believe one
of two problems caused it. The cooling system was suspect - So could
have overheated the head and caused the valve clearances to get too
tight. The other was the car had been sitting for a long while and old
varnishy gas can gunk up the valves. I tore that head off and sent it
to be rebuilt (needed hardened seats anyway). No bent pushrods since
- knock on wood.
Author:  Doc [ Fri Aug 29, 2003 9:06 am ]
Post subject: 
Do you have a cam card or spec sheet on this grind?

Check for valve spring coil bind and for clearance between the bottom of the valve retainer ant the top of the valve guide, you need at least .050 clearance.

The other cause is the "sticky valve guide" issue already touched on.
Time to take some measurments.
DD
Author:  Charrlie_S [ Fri Aug 29, 2003 10:13 am ]
Post subject: 
Crane Camshaft Specification Card
Part Number: 720771
Grind Number: F-218/2933-12
Engine Ident: 1960-1985 PLYMOUTH-DODGE SLANT 6 CYLINDER
170-198-225 CU. IN. GOOD IDLE, DAILY
USAGE & OFF ROAD, HIGHWAY TOWING

VALVE SETTING: INTAKE .022 EXHAUST .022 ----> HOT

LIFT: INTAKE @CAM 2933 @VALVE 440 ROCKER ARM RATIO
EXHAUST @CAM 2933 @VALVE 440 1.5
ALL LIFTS ARE BASED ON ZERO LASH AND THEORETICAL ROCKER ARM RATIOS

CAM TIMING OPENS CLOSES ADV DURATION
@ .014 INTAKE 28 BTDC 72 ABDC 280 °
TAPPET LIFT EXHAUST 72 BBDC 28 ATDC 280 °

SPRING REQUIREMENTS
TRIPLE DUAL OUTER INNER
PART NUMBER 99838

LOADS:
CLOSED 110 LBS @ 1.688 OR 1 11/16
OPEN 281 LBS @ 1.297
RECOMMENDED RPM
RANGE WITH MATCHING COMPONENTS
MINIMUM RPM 1500
MAXIMUM RPM 4000
VALVE FLOAT 5500

CAM TIMING OPENS CLOSES MAX LIFT DURATION
@ .050 INTAKE 2 BTDC 36 ABDC 107 °ATDC 218 °
TAPPET LIFT EXHAUST 46 BBDC (8) BTDC 117 °BTDC 218 °

REMARKS:
USE WITH CRANE RETAINER PART #99954.
Author:  Dennis Weaver [ Fri Aug 29, 2003 10:29 am ]
Post subject: 
...I assume you're getting good oil flow to the head, yes? Where I live, a mud dauber wasp can plug up a small hole faster than you can turn around...

"DW"
Author:  MitchB [ Sat Aug 30, 2003 7:36 am ]
Post subject:  Re: Cam grind and this sucks
Quote:
Fellas,
DD asked what cam I used that I was so happy with. The cam was a crane 720771. Works great when the engine WAS running.

However last night, I bent 2 push rods. One popped off and I found the #1 intake valve partially stuck open. It popped free, but I wonder if the machine shop who did my head work didn't check the stem to guide clearance. Also #1 exhaust was bent, but still on. Engine runs fine, compression is still good so no valves were mashed into the piston, but I wonder what caused this in the first place? Geez, now I don't trust this motor AGAIN!! Sucks doesn't it?? Anybody else ever have this happen to them?
Remember that coolant flows from the back of the head to the front, so the #1 valves will run hotter than the rest. I bent the #1 exhaust pushrod after the valve siezed in the guide. The valve hung open and kissed the piston. No damage to the piston. In my case, the valve-to-guide clearances were good. However, I ran the engine too lean and with too much spark advance. This caused the valves to run too hot and led to the siezed valve. In your case, I would pull the head and check everything. If you found the #1 intake valve stuck open, then the guide is already ruined. After that, check for proper oiling, coolant temp, carb jetting and spark timing.

Mitch
Author:  bud L. [ Sat Aug 30, 2003 4:33 pm ]
Post subject:  ?
Speaking as one who has done a few heads, I'll give you a couple of scenarios I've seen.
Some customers on a budget, will try to skimp, and want to reuse the old valves. If the valves are sufficiently worn, the stems will be 'hourglass shaped'. The rebuilder will have a tough time reading the stem to guide clearance, and will tend to make them tight at the ends of the valve lift trying to keep the clearance right in the middle(necked down area of the stem).
Another problem is dirt. The stem and guides have to be spotlessly clean, with only clean lube. The smallest speck of grit will gall the stem and stick a valve.
V. stems are surprisingly soft. The stems should be polished and handled carefully. just 'clinking' the valves together can dent the stem and raise a burr, which will definitely stick a valve.
Get the correct length pushrods. If the rocker geometry is wrong, you introduce all kinds of extra problems.
Drill a small hole (1/16") in the edge of the thermostat, so it'll tend to bleed off air in the system. If you get a bubble of air in the head, you can overheat the engine.
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