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Sun Nov 01, 2009 9:17 pm

I have a '72 bus with stock 1700 with dual Weber carbs. My alternator is going dead on me. I drove down to get some gas and she wouldn't start when I went to leave. I had my mom come jump me and on the way home she saw a big puff of smoke about the same time my oil light popped on. I got her home (about a block) and shut her down. Checked the oil... no loss... So i let her sit for a while and went out and got it started. I was hearing a pretty good knock from the right side (if standing at the back facing engine) but that went away somewhat. However, the exhaust on that side has significantly less pressure coming out of the pipe than the left.

Any thoughts??

Sun Nov 01, 2009 9:23 pm

the puff of white smoke & loss of power is usually indicative of a dropped valve.

don't know what the oil light has to do with it though.
do a compression test.

Sun Nov 01, 2009 10:45 pm

sounds like a dropped valve / valve seat. Did the oil light stay on or just come on for a second?

I am thinking that lifter float when the valve hung open, opened up the lifter bore oil passage for a second since T4 lifters can come all the way out of their bores.

When it cools down, check your valve adjustment on the weak side and see if one of the valves has excessive or strange clearance now.

Mon Nov 02, 2009 7:26 am

Please excuse my stupidity... when people say "dropped valve" I have a hard time picturing what that actually means. Does the valve actually drop out of the head... wouldn't that result in a lot bigger problem that I have... such as destroying the piston and anything else that might get in its way?

I'm just confused by what this actually means.

Thanks

Drew

Mon Nov 02, 2009 7:37 am

the valve drops out of the head or the seat drops out of the head. Type 4 motors are famous for dropped seats. The valve sticks partially open and the puff of smoke could have been oil pulled through the guide when that happens. The clatter is the rocker arm being loose as to adjustment because even if the valve seat goes back it usually cocks a little so one valve is too loose. When the valve sticks open because the seat is out, there is a lot of play on that rocker arm. The lifter on a type 4 has nothing holding it in except the pressure from the valve. That can cause it to come far enough out of the bore that the oil passage near it opens and that dropped your oil pressure. Like I said, pull the valve cover on that side and see what you find.

Mon Nov 02, 2009 7:38 am

You're picturing it right. And you described a "pretty good knock" on the right... bummer.

A dropped valve can punch a hole in the piston, or get bent by it. A dropped valve seat is a little less traumatic, but still sucks. Pull that valve cover off and have a look.

Mon Nov 02, 2009 9:39 am

there are a number of reasons why a valve could quit working--which SGKent explained well, as usual.

the term "dropped valve" is just a general statement for "valve not working".

Mon Nov 02, 2009 9:58 am

borninabus wrote: the puff of white smoke & loss of power is usually indicative of a dropped valve.

This thread is so dismal...The kid never even said, "loss of power" in the OP.
I've dropped a few seats (see pic below) and never did it smoke! I've driven 1200 miles with a dropped seat, again, no smoke.

"A big puff of smoke about the same time my oil light popped on"...that's the clue. Was it so small the driver didn't notice? Was it a huge white cloud? (valve guide) Did the oil light stay on or just flicker? And then the knock that went away...That's concerning.

A compression check is never a bad idea...and sure you can pull valve covers and compare valve heights.

No smoke or knock when these two dropped at the same time...well maybe some knock, but I was 3 miles from home and didn't hear it. (but the piston felt it)

Mon Nov 02, 2009 7:39 pm

I'm away at college now... I won't have a chance to look at it again for a couple of weeks. I'm not really sure of the color of the smoke, but there was a slight loss of power.

The oil light would only come on at idle... when I would rev it up the light would go out. Also, I let it sit and cool for a while... when I went out and started it back up, the oil light didn't come on at all.

Thanks

Drew