HELP! I lost 1200 rpm!
 

Yesterday I got the chance to run my boat hard for the first time this season, and it was not pretty. The boat felt like it didn't want to get on plane and I could barely hit 4000 rpm. Last season it snapped on plane and I could touch 5200 rpm. I had the engine out over the winter. Here are the specs and what I did to it:
Specs:
Small Block Chevy 406
Vortec Heads
Installed new last season approx 30 hours on it
Alpha outdrive
21p Rapture prop

Mods:
Pulled Outdrive
Pulled Engine
Removed Heads
Removed Oil Pan
Installed new oil pan (with dipstick welded in)and pickup
Re - Installed heads With no mods
Re-installed engine
Added Eddie Marine oil cooler and perma cool stat
Replaced stock coil with MSD blaster coil
Installed new bosch platinum plugs
Had Alpha professionally rebuilt including new seals, and lower gear set.
Reinstalled drive

Before starting I primed with an oil pump primer
Initially I had the timing out and could not get it to fire, so i did crank on her quite a bit before she took.

Engine starts easy and sounds normal (except I think one or two rocker arms may be out of adjustment), but it just doesn't have any grunt.

What could cause this massive power loss? I suspect that my valve train could be a little loose. Could that cause a 25-30% drop in power. How do I go about finding the problem?

Regards
Mike Olson

If it is loose it could yes. You would not be opening your valves properly. Timing?

Verified timing yesterday. 12 degrees initial advance, 34 total. Just like last year.

ttt

What kind of carb? How's the oil pressure? Could the crank be submerged with the new pan?

Carb is an edelbrock performer 750 cfm model # 1410. Oil pressure looks perfect, roughly 70 psi at wot, and 40 psi at idle. Same as last year. The pan is a milodon 7 qt pan for early sbc's. It's pretty similar to the old pan just kicked out at the bottom a little. I added the universal dipstick because my exhaust interfered with the block mount dipstick. I don't think that the crank is submerged, but I can probably do a rough check based on the dipstick. Could that cause such a major power loss?

Thanks!
Mike

Well, it doesn't happen often, but submerging a crank could cause something like you are describing. All things being equal, and the pan being the only variable, that would be the first place I would look- especially on a stroked SBC.

As for the carb, that would be the second place I would look. Sounds like the secondaries aren't opening...

Who adjusted your rocker arms? If some are off, some may be too tight, bad news. Your power loss seems to be accross the board. Are your wires (spark) hooked up right?

RPM Loss
 

Olysan.
Check all the small stuff, timing, are the plugs gapped properly and wires set up with the correct firing order.
Did you possibly hook up the throttle linkage in a different position not allowing you to get full throttle?
Valve adjustment would effect the motor pull the covers and have someone reset them.
Could you be lacking fuel, is there something crimping the fuel line?
Is is possible you may have a loose connecton on the inlet fuel line causing some lack of fuel.
Is your water seperator new? I have seen filters with three inches of water in them and one inch of fuel due to a bad batch of fuel from some marina with a water problem.
Post your findings so we all know what happened.
Tank U

Thanks for the feedback guys that gives me a few things to look at.

BBToys: The fuel lines are good, and the water seperator is new, I will pull it and check for water. I did make some minor adjustments to my throttle linkage, so I will verify that It's opening fully, but wouldn't a carb problem be more of a top end only issue? I feel like power is down across the board.

John B: I did the rocker arms on the stand. I was really paranoid about getting them to tight, so if anything I think that they're loose. I guess we'll know tomorrow when I pull the valve covers.

Havasu: You're scaring me. Pulling the pan means pulling the engine, and I really don't want to do that. I'll bite the bullet and check it tomorrow. Wouldn't submerging the crank create frothy oil, and if so what symptoms would that produce. In other words are there any other indications that the crank is submerged?

Here's my plan:

Replace Bosch plugs with a new set of Champion RS12YC plugs, because that is what I ran last year.

Verify all wires are correct, pull distributor cap, verify condition.

Pull valve covers and adjust rockers while engine is running.

Check oil level vs. crank

Verify throttle linkage adjustment

Verify water seperator is full of fuel

Post results!

Thanks again.

Mike

Well Mike...
 

Don't mean to scare you.

One time, when I changed my pan, they gave me the wrong dipstick...and I didn't realize I was overfilling the pan. Very few symptoms, but the pressure was a little erratic. I don't think that's your problem, but it doesn't hurt to check...

I think all these guys are right on track. When troubleshooting, I tend to start with the simple things, like making sure the linkage is set correctly, wires, etc.

Something I just thought of...did you have an external ballast resistor on the stock coil? I think that MSD coil has an internal one...just a thought.

Jeff

I'm not sure about the ballast resistor? My ignition is staright stock T-bolt IV salvaged from my old 350 magnum. When I changed out the coil I just swapped the wires over nothing else.

I'm not familiar with that ignition, maybe someone could chime in. On my old Volvo ignition, the ballast resistor was mounted in-line on the wire to the positive side of the coil...it was fairly close to the coil. It was an inch or so long, and had plugs on each side.

The resistor limits the voltage to the coil, to keep it from self-destructing. If you still have a resistor in-line with a coil that has an internal one, you may get a very weak spark. Hard starting, power loss, etc.

A quick test would be to put a voltmeter on the positive side of the coil while it's running (or the key on). You should get 12-14 volts. If there is a resistor, it may only read 10 volts or so.

Once again, just thinking out loud.

I pulled the plugs this morning. 1 & 3 look like new almost like they've never even fired. The wires were tight when I pulled them, and I verified my firing order. The rest look pretty good, a couple were a little on the dark side, and a couple were a little to clean looking, but generally pretty good except 1&3. Could this be a coil related problem or does this indicate something else?

Did they smell like gas?
 

Generally, if they are not firing, they will smell like gas.

If I want a quick test to see if they are firing, I will usually take the wire off, and place the exposed (brass) end 1/4" from the engine block. Now, crank the engine for a couple seconds...there should be a spark jumping from the end to the block.

As for the coil, a weak spark may cause this...but there could be other reasons. If unsure, Perhaps you should throw the old coil back on to see if there is a difference.

If there is a strong spark, and at the right time (firing order, timing checked), and the plugs do not smell like gas, then I would look for a fuel problem.

Did you verify the valve adjustment? Also, I don't want to concern you, but those cylinders being next to each other, perhaps a leakdown test is in order, just to be safe.

Just curious... how did you set the valves initially? Should be 1/2 turn of the rocker nut after the push rod stops spinning freely. Can you hear any valve train ticking?

BT :cool:

I'm with Havasu....throw the old coil back in and check it then. Also, there is no sure fire way to check your cap other than replacing it. Even a slight drop would be enough for a hairline crack (invisible) and thats enough to ef everything up........

Okay, the heat index was 110 here today and my driveway (where I work on the boat) gets sun all day so I didn't get to the valve train.

I don't remember a strong gas smell when I changed the plugs. Not sure if it matters, but the engine hasn't run since thursday. I did notice some oil on #1.

I did change the plugs to champion RS12YC gapped @ .040 - exactly what I ran last year, and I did replace the MSD coil with the original merc coil. I also checked my throttle adjustment, and it was good. When I started the engine it seemed to run significantly smoother, so I thought I might have solved the problem.

WRONG! I pulled the boat up to the nearest launch, dropped it in and hit the gas. Same sluggish acceleration and no top end. It seems to run fine no strange noises just a dog. I had the GPS with me today, and top speed was 42 @ 4000 rpm. That's a loss of 12 mph, and 1200 rpm.

I'm going to take a look at the plugs tomorrow morning, and try and adjust the valves next week sometime.

Blue Thunder - I used the procedure that you described. I guess my concern is that I might have had the crank 180 degrees out. At times I hear what sounds like 1 or 2 valves ticking, but that's it.

Thanks everyone for the help to this point.

Mike

When setting valves, I always turn the crank until about 1/8 rev past when the intake valve closes, then I do that cylinder. I continue this on each cylinder. 180 out doesn't mean anything this way. Also.. others disagree, but I don't like setting the valves with the engine running... too much uncertainty.

BT :cool:

Where's Ray?
 

There was a guy on another board...he raced Pro Street I think. Anyway, on his boat, he never adjusted his rocker arms past pushrod resistance on his hydraulic cams- he said it was worth 20HP more on the dyno....for a loose valve train.

olysan- still thinking outloud...perhaps you could throw an ohmmeter on each plug wire...you may have damaged the core(s) during the r&r.

This sounds like a repeat of my disaster last year. Those plugs that are white could be way lean. Had this happen after I changed an intake manifold. Think I had a air leak at a couple cylinders and didn't diagnose the problem until I melted a couple pistons. My engine started and ran fine, just down on power. I had almost the same drop in RPM's that you're seeing.

I'm going to pull the new plugs and take another look, I made a couple of wot passes yesterday.

JON242,

Where do you think the air leak was?

Havasu,

Makes sense if 1 & 3 look the same I'll try an ohmmeter.

Just an idea, could the outdrive have been rebuilt with different gears?

Not sure where the leak was but I suspect maybe from the lifter valley into the intake port. One of my symptoms was if I ran at WOT for about 10 seconds it would start to act like it was running out of fuel, then throttle back and it would be OK.

(except I think one or two rocker arms may be out of adjustment),

I would start here !

Here's a pic of my plugs. Same thing on 1 & 3, they look almost new. You can't see it in the pic, but it does look like they've been sparking just not igniting anything. 4 was damaged during extraction. I thought 8 looked lean when I pulled it, but it looks okay to me now.

I still haven't torn into the valve train, I'm hoping to get after that tonight.

Let me know what you guys think.

I had a similar problem with my 454 Mag, Last year it ended up being a bad/clogged injector. Is yours an EFI Setup or Carb? My plugs looked the same, The non firing cylinder was like new.

Mine's a carb.

Are you sure that you have good wires going to those plugs? How about the cap and rotor? Good? There is nothing happening in those cylinders. Have you painted anything... maybe the plugs aren't grounding? You should at least have the effects of combustion on the threads like the others. Can you get any close-up pics of those plugs?

I would think that if you had an air leak it would be lean, but it would still fire to some degree and you'd see something happening on the threads. Also, with a very lean condition you'd have some damaged plugs.

And one last question (and this may be stupid sounding), but did you by chance stick anything down in the intake ports to keep out critters and such and then forget to remove them upon reassembly?

I don't think you're getting fuel to those cylinders.

I put an ohm meter on the wires last night and they all checked out, the cap and rotor look okay. I can see signs of spark when I look real close at those plugs, so I don't think its a spark problem.

I've been trying to figure out what could have gotten (or been put) in the intake runners, but I don't think I ever had them blocked. I was under some pressure to get it back together, and I'm not above doing something stupid.

I'm going to try and get the valve covers off tonight and we'll see where that gets us. If the intake vale on 1 & 3 isn't opening at all could that be the prob? Like if the rocker slipped off the pushrod?

Have you tried a compression test?

rpm loss
 

You mentioned earlier that it almost seemed as though it was a lack of fuel!
Could there be a fuel pump problem?
Was the motor changing rpm slower then faster?
I had a problem on time with contamination in the fuel tank a plastic cap floating around in the tank, inconsistant fuel delivery causing rpm drops only on occasion, a tough on to trouble shoot, we pulled the fuel tank and found the plastic plug.
Post your findings.
Thanks

It's Back!
 

Yesterday morning before work I decided to start breaking down the exhaust etc so that I could pull the valve covers. i decided to pull all the plug wires and get them out of the way. When I did this I noticed that the positions of 1 & 3 were reversed in my wire seperator hmmmmm....... I'd checked those wires at least five times but they evidently were twisted behind the exhaust and a pull on one moved both.

To make a long story short, swapped the wires and it's all good.

Thanks for all the help.

Glad to hear it!
 

:D

Plug wires
 

Looks like your going boating!
Thanks for posting your findings.
They should make a design change in all ingition wires with different colors and or a more perminant type of method to stick on or crimp on a solid number with a stainless steel number.
I typically like to use a paint stick, and write the cylinder number on the plug end of the wire.
Have a great day
Brian