Topic: holed piston or twisted cam or ?

[Odge]

I was blasting home last night and poof! I lost power on the two right side cylinders. I was stuck on the freeway overpass onto highway 24 on Oakland which must be half a mile long and 200 feet high with cars flying by at 70+. How can my baby let me down like this?! After pushing it home for 3 miles or so, I have been trying to figure out the extent of the damage. As far as I can tell, it's not the ignition, and it is unlikely that two carbs fail simultaenously. It blows a lot of smoke out of the breather, and it back fires through the carbs from time to time. Another wierd thing- the tachometer stopped working! I am thinking this means it is cam related, but as we know there is only one and the left cylinders are still firing. Is it possible that the cam broke? I am thinking at minimum i need to pull the engine Anybody have any experience or wisdom to share?

[bistromath]

You got it. Sounds like a broken camshaft. It happens, usually from a careless rebuild where some of the oil passages get plugged by gasket goop. If you're lucky, the cam bearings aren't shot.

[Gordon]

Ouch!  Did you hear any screeching before the break-down? 

[magnum56]

I was blasting home last night and poof! I lost power on the two right side cylinders. I was stuck on the freeway overpass onto highway 24 on Oakland which must be half a mile long and 200 feet high with cars flying by at 70+. How can my baby let me down like this?! After pushing it home for 3 miles or so, I have been trying to figure out the extent of the damage. As far as I can tell, it's not the ignition, and it is unlikely that two carbs fail simultaenously. It blows a lot of smoke out of the breather, and it back fires through the carbs from time to time. Another wierd thing- the tachometer stopped working! I am thinking this means it is cam related, but as we know there is only one and the left cylinders are still firing. Is it possible that the cam broke? I am thinking at minimum i need to pull the engine Anybody have any experience or wisdom to share?

From your description, it is very possible that you have indeed broken the cam.  It may be difficult to tell for certain without pulling the engine and removing the rocker cover, because without a "load", even a new 2 piece cam    may "appear" to turn and actuate the rockers/valves.    

With that being said you may want to first investigate further by removing the plugs and rocker adjustment covers to determine if the compression stroke related to 3 & 4 still jives with your timing marks.    
 

[MCRider]

I was blasting home last night and poof! I lost power on the two right side cylinders. I was stuck on the freeway overpass onto highway 24 on Oakland which must be half a mile long and 200 feet high with cars flying by at 70+. How can my baby let me down like this?! After pushing it home for 3 miles or so, I have been trying to figure out the extent of the damage. As far as I can tell, it's not the ignition, and it is unlikely that two carbs fail simultaenously. It blows a lot of smoke out of the breather, and it back fires through the carbs from time to time. Another wierd thing- the tachometer stopped working! I am thinking this means it is cam related, but as we know there is only one and the left cylinders are still firing. Is it possible that the cam broke? I am thinking at minimum i need to pull the engine Anybody have any experience or wisdom to share?

From your description, it is very possible that you have indeed broken the cam.  It may be difficult to tell for certain without pulling the engine and removing the rocker cover, because without a "load", even a new 2 piece cam    may "appear" to turn and actuate the rockers/valves.    

With that being said you may want to first investigate further by removing the plugs and rocker adjustment covers to determine if the compression stroke related to 3 & 4 still jives with your timing marks.    
 

I have broken one, and seen 2 others. It is quite easy to know. Just pull all tappet covers, turn it over and watch. If its broke, 3 and 4 in and ex valves will not be moving. all the friction in the world between the 2 ends of the cam will not over come the valve spring force.

The tach is driven by the 3/4 end of the cam. And it ain't movin.

Oh and by the way... it's broken.

PS: Never on a stocker, always on one that's been apart. Has yours been worked on? A little piece of debris, likely silicon gasket sealer, gets stuck in the oil orifice that feeds the cam. It is a very tiny hole. The offending side, usually 3/4 for some reason, seizes in the cam holder, which is also toast. When mine seized there was a very distinct "PING" as the cam was twisted in half.  Probably 4 rockers too. No reason it can't be 1/2, just the luck of the draw.