73 bus engine problems: valve way out of adjustment

I adjusted valves 2 weeks ago.

yesterday, I had extreme power loss.

I opened up the valve cover, and
cylinder # 3 (front left of engine) had
about 1/4" clearance on intake valve. It
was firing out the carb, and pushing fuel/
air out of carb.

What would cause this? the "lock nut" was
tight....

bent push rod?
flat spot on cam suddenly?
cam follower suddenly shaved off 1/4"?

Jen

wrote:
> I adjusted valves 2 weeks ago.
>
> yesterday, I had extreme power loss.
>
> I opened up the valve cover, and
> cylinder # 3 (front left of engine) had
> about 1/4" clearance on intake valve. It
> was firing out the carb, and pushing fuel/
> air out of carb.
>
> What would cause this? the "lock nut" was
> tight....
>
> bent push rod?
> flat spot on cam suddenly?
> cam follower suddenly shaved off 1/4"?
>
> Jen
>
Valve seat came loose, or is now cocked slightly.
That holds the valve head more in the "open" position
and moves the stem "inward".

Since the valve can't seal, the cyl fires back thru the carb.

Eventually, the seat will (maybe) move some more and the
valve head will bang into the piston and the engine will
be toast.

As a check on my theory, remove the rocker arm shaft.
Hold a straightedge across the valve stems. If #3 is
further in, the theory fits.

--

Speedy Jim
http://www.nls.net/mp/volks/

I'll check this...

engine has made a noise ever since I bought it, a
knock sound (low frequency,maybe 4X - 6X per
second)... Could the valve seat be making this
noise?

Thanks,

Jen

wrote:

> I'll check this...
>
> engine has made a noise ever since I bought it, a
> knock sound (low frequency,maybe 4X - 6X per
> second)... Could the valve seat be making this
> noise?
>
> Thanks,
>
> Jen
>
That could be the valve head hitting the piston.

Jim

valve #3 stem was approx 1/4"
shorter when measured with a
straight edge compared to the
other valve stems.

Engine is out of the bus,
head has been removed.

guess what? The speedy answer
that Speedy Jim gave me is correct.

The valve seat moved all around in
the head. The knocking was the
valve head hitting the piston.

The piston now has approximately
1/8" deep gouge into it...

Makes me think either a)connecting
rod has been worn b)bearings on
connecting rod have been worn or c)
bearings on crank have been worn.

Any ideas or suggestions on what
to do about this? replace the piston?
It isn't cracked. less than 1/8" deep
gouge into it.

I am looking into getting the head
rebuilt, or just buy a new one. Any
suggestions for this?

Thanks to Speedy Jim!


Jen

wrote:

> valve #3 stem was approx 1/4"
> shorter when measured with a
> straight edge compared to the
> other valve stems.
>
> Engine is out of the bus,
> head has been removed.
>
> guess what? The speedy answer
> that Speedy Jim gave me is correct.
>
> The valve seat moved all around in
> the head. The knocking was the
> valve head hitting the piston.
>
> The piston now has approximately
> 1/8" deep gouge into it...
>
> Makes me think either a)connecting
> rod has been worn b)bearings on
> connecting rod have been worn or c)
> bearings on crank have been worn.
>
> Any ideas or suggestions on what
> to do about this? replace the piston?
> It isn't cracked. less than 1/8" deep
> gouge into it.
>
> I am looking into getting the head
> rebuilt, or just buy a new one. Any
> suggestions for this?
>
> Thanks to Speedy Jim!
>
>
> Jen
>
Actually, the piston/rod may have come thru OK, just dented.
(No guarantess...)

I vote for a new head; pressing/shrinking new seats
in is beyond the ability of any normal shop.

Jim

Something (any ideas what?) caused
the valve seat come out of where it
was pressed into.

The head got chewed up a bit when
the seat came out. The seat is
dented from the valve not hitting
it flush..

I have a milling machine that is
computer controlled. I would like
to machine a new valve seat.

I'll have to mill the receiving hole
on the head to a larger diameter,
because the edges are chewed
up. Also make a new seat on
the lathe, with large outer diameter
to fit in the widened hole.

I looked around and found rebuilt
heads for $189. Ne heads is $500.

This head with the
bad valve doesn't have anything
else wrong with it, and I think I may
be able to repair it.

I'll give it a try while I research
cheaper parts.

Jen

wrote:
> Something (any ideas what?) caused
> the valve seat come out of where it
> was pressed into.

Overheating? Pinging? Just came to the end of it's natural lifespan?
Makes me wonder if the other seats would soon follow. (get you worried yet?)



> The head got chewed up a bit when
> the seat came out. The seat is
> dented from the valve not hitting
> it flush..

I would also inspect the valve guide carefully. Especially since you
need it to be straight and tight when working on the seat, because you
need to use the valve guide when lining up the seat and machining it.


> I'll have to mill the receiving hole
> on the head to a larger diameter,
> because the edges are chewed
> up.

Is there enough room to safely do that? Without risking cracks?
You will need to know fitting tolerances.


Jan