Why I Couldn't Get RPMS !?
 

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

I've been playing with big blocks for 30 years and I've never seen a broken guide plate either. Did you find the pieces? It's hard to believe a pushrod can cause that kind of damage without bending or breaking. Are your rockers hitting valve spring retainers by any chance? Could you post more pictures?

Kirk,

Check the pivot on the rockers to make sure the spherical face is towards the head and the flat face is towards the adjusting nut. I believe the correct pushrod length for your Gen VI motor when changing to the adjustable valve train are 7.55" ex and 8.55" intake (could be the other way, but those are the right lengths). If the spherical side was towards the adj. nut or the pushrod lengths wrong, your rocker geometry would be off causing all sorts of side loads on the valve stem. Ring me tonight with the news from your head doctor.

Mark

That is a strange looking pic! I have never seen rockers running like that! I know if it were me, I would replace the guides, valves rockers and everything. Running as long as you stated with that kind of side load could weaken some parts in a hurry! I would use the Jesel sportsman rockers and guides. They have tons of experience is 9800 RPM big blocks where geometry is absolutely critical.
I would gues the tips and bearings in your rockers are trashed.

I just ran into and issue with a guide plate problem,had to extend the pushrod length to solve these issues,all due to lifter change.....crane to comp cam! problems were all found and solved during adjustment....actually had to lengthen pushrods .225 to get the stems up past the guide plates or would have run into that exact problem!!!!these were manley hardened 3/8 w 3/8 guides and the bevel on the pushrod was in the guide plate when the valves were closed!have also seen that problem when the stud size on the guide plate hole was bigger than the stud,allowed the guide plate to mount crooked!leaving the exact problem that I can see in your photo....rockers being alighned off center to the valve stem!

Changing cams, lifters, valve springs can all affect pushrod length. There is no set pushrod length when you use aftermarket stuff. Usually, if you use one company's stuff, they size everything. But if you buy a cam from one company and valve springs and retainers from another, you may need custom length pushrods. The key is to center the tip of the roller on the valve without coming into contact withanything else. In extreme cases you may have to grind clearence in the rocker.

What I do to check the pushrod length is use a magic marker or Dykem blue to mark the valve stem. Then get the cam for the valve you're working with on it's base circle. Place the rocker on the stud and wiggle it slightly. The horizontal line left on the valve stem should be on the inboard (towards the intake) third of the valve tip. If the mark is in the middle, or toward the outboard side, the pushrod is too long. Because of the rocker geometry, the rocker tip will travel across the center of the valve stem as the valve opens with the proper length pushrods.

Mark S.

My push rods are 7.5" and 8.5". My Lifters are the aftermarket roller, horizontal bar by Federal Mogal(now out of business)

I did ruin (3) rockers. The heads are being inspected. I would anticipate several new valves, all new guides and then reassembly.

I will then inspect the valve train with the procedure described by Mark above. I trust nobody anymore!!

Just because is says machine or speed shop above the door, it doesn't mean it is one!

20.9 hours on the engine.

I have Dart aluminum heads and use the Comp Cams pushrod guide plates.

BTW, The Iron Eagle cast iron heads have had A LOT of core shift issues. Talk to Jack/Budah he can tell you all about it! "Doug" (Pure Adreniline) here on OSO had major issues with those heads about a month ago and Jack/Budah fixed him up. Also, check to make sure the pushrods aren't hitting the sides of the holes in head castings.

Upgrade the rockers
 

Should I look into a shaft mounted set up? What would cause (3) to come off like that?

Here's what I'm considering:

http://www.jesel.com/

Pantera24-650/ have been running the Jesel Competition Series with no problems. But as Breathe Later stated, you really have to pay attention to the geometry when you setup as you have you have less adjustment available with the Jesel.