Well, I dropped down to a 24P Prop in attempt to get higher RPMS out of my 650 HP motor. (See previous posts)

http://www.offshoreonly.com/forums/s...threadid=55657

After making (2) runs, only able to get 4950 - 5000 RPM, I pulled the throttle back to slow down and the port exhaust started sounding funny...I shut it down, pulled the boat out, and removed the port valve cover to find this:

A similar sitution occured on the dyno. If the engine was held at 4000 RPM for a few seconds, the valve guides would hold open valves not allowing them to close. The builder disassembled the heads and honed the guides for proper clearance. Seemed to work on the dyno, but what would cause the above?

Since installing the motor, I could not get any power at higher RPMs. I used to turn a 29P at over 5000 RPM, yet since the rebuild, I wasn't able to get over 4650 RPM

Before I go ballistic, I'd like some sound input on what would cause this.

What was done on the rebuild? Same parts just new rings, valvejob & bearing?

Total rebuild with reuse of the rods, pistons and valves.

Heads were pressure tested, new guides installed, new springs, new keepers, and a valve job performed.

As stated above, we were experiencing a loss of power at high RPMs on the dyno, and then a rocker came off of a valve just like above. We pulled the heads and measured the stem to guide clearance and the guides were actually tapered. The machinist honed the guides and we tested it again on the dyno. Appeared to be corrected.

All summer I have been trying to solve a problem of not being able to turn a 29P, 28P or 27P prop over 4650 RPM so I tried a 24P. I got 5000 RPM and then the above occured.

I think the problem has been there from day one and thats why I couldn't spin the higher pitch props.

The boat is a 24' Pantera 4500#. Engine dyno'd out at 650 HP. 28P props should be no problem to turn.

Hard to tell from the picture, but it looks like the rockers have rotated off the valve stem. It looks like you have polylocks, but I don't see any guideplates to keep the pushrods in line.

If there aren't guideplates, that could be the source of your problem. As you know, since BBC heads have canted valves the pushrod has a slight angle and will put a side load on the rocker and hence the valve stem and guide without guideplates (or shaft mounted rockers).

You don't see the guide plates because they broke off...what caused them to break?

Your guideplates broke off? I have never seen or heard of that happening, they are generally made of hardened steel, at least when used with hardened pushrods, which most are. The guideplates are secured by the rocker stud and are very rigid.

Are you using aftermarket cylinder heads with relocated valves or non-stock valve angles?

The picture above is the port side. i just pulled the starboard side cover and it appears that # 4 cylinder was running like this for a long time. I guess thats why I didn't have the full 650HP to turn larger props. Looks like its going to be a fun Monday talking to the engine guy!!

I too recently had my 454's totally rebuilt after owning the boat for about a year. During the initial year, I was in the valve train a few times, replaced a cam etc. Noticed that a few push-rods had been changed somewhere along the way and I had broke/bent one myself during the initial year.

When I had them rebuilt, the mechanic informed me the the push-rods were 5/16" with 7/16" plates and that he had found a couple to the crane rocks (same as yours) off the valve stem too. This causes side loads on the push-rods and was probably the reason for the bent and breaking push-rods as well as the reason the rocks weren't staying on the valve. He of course changed the plates and I haven't had a re-occurrence since. So, check to make sure the push-rods and guide plates matched. Let me know what you guys find.

Al

Thanks Al -

I have Dart heads, which I think causes the push rod and valve stem geometry to be a little bit off.

Anyone know which pushrod guides are best for Dart Heads? I thing they are Iron Eagle