Heads removed and replaced now I don't have any power.

[drun_trucker]

So some time back I posted or asked about swapping out a marine motor for an automotive. After a bunch of trouble I got the auto motor swapped out. I got it timed and ran fine in neutral. However when under load it would get over 2100 rpm (that was still on the trailer at the launch). On the lake I get up to 3000 rpm.

After have gone over just about all I could think of I deduced it must have been the auto cam...

Therefore I fixed the crack on the marine block and began putting that back together, fast forward a few days and here we are again. Motor is back together and in the boat. It ran like a top prior to removing except for taking water into the block. I got that problem fixed but now I'm back to no power.

I am thinking that I must have an issue setting valve lash. I even did that to spec in the service manual.

Please please please, throw some ideas and questions at me.

Fuel is good and filters are new, compression is great, spark is fine. Timing is 8* BTDC, advance is 22*, all ALL other components are original to the application that ran perfect prior to removal.

 

[Bt Doctur]

If you can assemble a motor and have it run , you must know enough.
So, tell us the type of motor this is because some rockers are torqued down and others are adjusted down to 3/4 lash.

 

[thumpar]

Have you checked compression? My guess would be valves or spark plug wires not in order.

 

[drun_trucker]

1990 Mercruiser 4.3L, Thunderbolt IV, it's pre Vortec and NO balance shaft
hydraulic roller lifters

Im about to loosen all rocker arm caps and start it tighten each until all the rattles are gone.

I really think my problem is in the valves. Oh and compression in good. 167 psi to 180 psi across the board.

 

[Hoosmatroos]

My guess was the same, spark plug wires swapped

 

[Bt Doctur]

that year is listed as 1 turn down from "0" lash

 

[drun_trucker]

Not plug wires, not cap, timing is correct, fuel is good, spark is good, compression is good.

Now...what EXACTLY is "0" lash? As this was my first complete rebuild in my life I am learning A LOT as I go. But I do have some confusion as to what or where the zero lash is. I hear it's when all vertical play is gone from the push rod, I have also heard it's when the rod can not be moved vertically or rotated.

If I had to guess, I am going way past the 1 turn past zero lash. Leaving exhaust valves open and not getting maximum power out of the combustion stroke...

Like I said before. I took this very motor out in PERFECT working condition. (except the crack in the valley and taking in water.) I picked up a used salvage truck motor which I used the block, cam, and timing gears from...got it all back together and in the boat had the same issue I'm having now.

I decided to repair the cracked block and reinstall it. I mean it was running perfect when I took it out it should be perfect going back in. Just hopefully I fixed the water issue. Again, fast forward to today. I fixed the crack as it's not taking on/in water to the block but I'm in the exact same spot as the swap out.

 

[alldodge]

Zero lash, with valve fully closed back off on the nut while holding the pushrod. You should be able to rotate the rod back and forth along with up and down. When this happens, start tightening slowly while moving the rod up and down. Soon as all up/down movement stops, this is zero lash. The rolling back and forth is of no issue, it is the up/down that is important.

Once zero lash is found, turn one more full turn and stop. Now go to the next valve that is fully closed.

 

[drun_trucker]

So that is basically the procedure that I followed. And I did it in the order that the manual stated. However the biggest difference is when I was getting zero lash I was making sure that wasn't any wiggle in the rod. Not taking into consideration that with one more full turn I would be eliminating the wiggle...does it seem that I may have valves being held open for too long?

 

[alldodge]

does it seem that I may have valves being held open for too long?

IMO, no
If the valves were open to long you will have a backfire through the carb or exhaust, and your compression will be bad.

167 psi to 180 psi across the board

What did the machine shop do to the heads, deck and cylinders?

 

[drun_trucker]

The "machine shop" did nothing. I ground out the crack and filled with JB Weld. I know it sounds crazy but it worked. The motor is bone stock.

 

[alldodge]

The 180 psi is a bit high for me, hence my question. How about lets go back to some basics. Check fuel pressure it should be 4-7 psi

 

[NHGuy]

Did you dissasemble the engine? The lifters need to stay in the same locations or you will need new lifters and cam. Once a lifter is run in to it's lobe that's where it spends it's life.
As far as valve settings you want to get to no vertical movement to be at zero lash. You will probably be able to wiggle a little sideways but don't concern with that. The pushrods bottoms must be in the lifters cups straight and the pushrods tops have to be in the rocker arm cups. Then you wiggle the pushrod vertically while gently turning the rocker nut until there is no vertical movement. From there do your 1 turn.

You may want to go half a turn past zero lash, that is the common way they are done now.

Here's a great description of how to sequence it. This writer uses the half turn method.


Slowly turn the motor over. When the exhaust valve just begins to open on the first cylinder in the firing order, adjust the intake valve by loosening the adjusting nut slightly while spinning the pushrod until you feel lash in the rocker arm. Tighten the adjusting nut until the slack is taken out of the rocker arm and pushrod. Lightly turn the pushrod with your fingers as you tighten the adjusting nut, and you should feel a point where there is a little resistance (this is called Zero Lash). Turn the adjusting nut 1/2 turn. Follow this procedure carefully adjusting each intake valve according to cylinder firing order.
When all of the intake valves have been set to the proper valve lash, you can adjust the exhaust valves. Utilizing the same procedure as with the intake valves, you need to turn the engine over until the intake pushrod moves all the way up and rotates just past maximum lift. Now the exhaust valve can be adjusted. When all of the intake and exhaust valves have been set with the proper lash, it is common for all the top engine builders to perform a double check by rotating the engine and checking each valve again, starting from the first cylinder in the firing order.

 

[Faztbullet]

On hyd rollers its one turn from zero lash

 

[keith2k455]

The 180 psi is a bit high for me, hence my question. How about lets go back to some basics. Check fuel pressure it should be 4-7 psi

You say it runs, but no power. Any knocking (pre-detonation) or other sounds? Did you degree your cam in right?

If you degreed the cam, I agree, back to basics. Fuel psi, plug gap, ignition timing then on to carb adjustment.

 

[drun_trucker]

Low on power

Re: 2001 mercruiser 4.3 - no power, 3600 WOT RPM

Here is a list of about every possible cause of low WOT there is.

Engine Won't Reach Operating RPM. Check

• Fuel condition. Type and Octane possibly old fuel
• Propeller pitch or diameter, damaged blades
• Restricted fuel pickup tube or anti siphon valve Fuel System Test
• Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
• Marine growth on hull and outdrive
• Wrong gear ratio in outdrive
• Restricted carburetor air intake (clogged flame arrestor)
• Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
• Poor cylinder compression Compression Test
• Carburetor defective, or wrong type.
• Fuel pump pressure and vacuum
• Boat overloaded, improperly loaded, or improperly trimmed.
• Engine Overheating
• Engine timing and ignition system operation
• Remote control cables and linkage for proper travel to open throttle plates fully.

In reference to this archived topic, http://forums.iboats.com/forum/engi...179-2001-mercruiser-4-3-no-power-3600-wot-rpm


I pulled a my motor (4.3L V6) due to a cracked block. I got a different block and swapped over all the other original parts. Timing is good, fuel is new, carb cleaned, new fuel tube and filters, oil at capacity, spark arrestor clean. I'm at a loss of where my power went.

When I took the heads off I removed the rocker arms, pushrods, lifters...I read that push rods could be different lengths could be causing a duration problem. I have read so many things my head is spinning. I just need some help.

Please, I know the post is old but its very relevant to me. original

 

[drun_trucker]

Not sure what you mean by degreeing in cam

 

[Fun Times]

Not sure what you mean by degreeing in cam

Here's a few videos for you to watch about degreeing a camshaft. http://www.bing.com/videos/search?q=degreeing+a+gm+camshaft&FORM=HDRSC3

I moved your post from the archive topic to here and put in a link for reference for anyone that may need it.
Just so you're aware, it's preferred that engine topics older then 90 days remain an archive unless it's your topic you started then there is no time limit set as long as you are working on the same issues...Thanks for understanding in advance and good luck on getting this one figured out.

 

[ihc1470]

First let me say that I am not familiar with this engine so some of the ideas that I am throwing into the mix are just crazy things I have run into in 40 plus years of turning wrenches in the auto and truck industries. I have seen vibration dampeners slip which then changes your timing mark. Might want to run #1 up to TDC and see where the marks are on the front end. Small rod or screw driver on top of piston and carefully turning engine over by had should get you close enough to know if an issue. What sort of vacuum reading are you getting with the engine running? There are several things that will affect your readings. Idle speeds, timing issues, leaky valves, low compression, elevation above sea level, etc. It is a wonderful tool to use once you understand what it is telling you. Check both idle and high rpm if it starts dropping off at higher rpm look for a restriction in the exhaust. I doubt you have any open valves with the compression readings you are getting. Check your primary wiring at the coil. If by chance the wires are switch around it can cause low voltage output. Plus terminal is the battery feed and minus goes to distributor. Bad coil? Measure the resistance with ohm meter and see if within specs. I have seen the coil to dist cap wires go bad and still be running but have very weak spark. How large of a gap can you get the spark to jump? I would look for a consistent 3/16 to maybe 1/4 inch. Not sure if carb or fuel injection but if carb did you by chance leave it mounted to the intake manifold and flip it over to clean gaskets? That can cause issues with the fine dirt getting up into the jets or plugging other passages. Fuel pressure was mentioned how about fuel flow? I ran into a piece of paper towel stuffed into a fuel line one time when an engine had been pulled but forgotten and left in. It actually ran for 3 years that I know of before it finally plugged enough to restrict the fuel flow. Was on a diesel engine in a fleet truck that had been shipped in to my location. Have no idea who had pulled the engine in the past but it was in the my fleet that length of time before acting up. Good luck in finding your issue. Bet it ends up being something very simple.

 

[alldodge]

Not sure what you mean by degreeing in cam

This is done to check that the cam is ground correctly and the keying on the crank and cam shafts are positioned correctly. IMO the 95% of the time they are correct and the 5% that is off, it's only +/- 2 degrees. most only one. For a standard rebuild I wouldn't do it. For a high left cam power rebuild you need to do it, tolerances are to close