Camshaft movement

[TMcDaniel]

So I've been working on my 2001 4.3l carburated mercruiser with alpha 1 gen 2. Weve been in the river tubing and island hopping alot this year and the boat ran great. A few weeks ago on our way out from the dock I noticed it took longer to plane out and my rpms were lower than usual (4000 instead of 4500). So we got to the island everything seemed fine stayed there for an hour or so and loaded up to go tubing. The first riders got on and again slow to plane and lower than usual rpm. They were on for about 10 min then the next group got on and it wouldn't get on a plane and wouldn't go above 3000 rpm. So we went back to the dock. Looked up on the forum and decided to change plugs wires cap and rotor. Next day went out on a test run and still the same except there was a loud knock sounded like the motor was going to blow up. Checked the oil and it was barely on the dip stick so I pulled up to the bank added 3 quarts and proceeded idle back to the dock and the knocking never went away. When I changed the plugs cylinder 2 plug was blown out not crushed but the ceramic was gone from the tip. Long story short I pulled the motor replaced the rod bearings and pistons. Put it back together took ot out fo a test run and about 20 min in motor started knocking and shortly after it locked up. Pulled the motor again found cylinder 1 and 2 rod bearings spun j badly damaged. Pulled the crank shaft off and found the main thrust bearing was trashed. Replaced 2 rods rod bearings and main bearings. When I was putting everything back together I noticed the camshaft moving front to back. Took out for another test and now in getting a different knock checkech all my lifters they seemed fine. Now my question could the cam be moving forward and back be causing the knock. Or does anyone have any other sugestions?

 

[alldodge]

There is a certain amount of play but ot that much. The play is listed in the GM or Merc rebuild manual.

When motor is being rebuilt, was the oil pump replaced, and bearings check for clearance using plastic gauge?
The crankshaft is being turned and oversize bearings used, correct?

 

[TMcDaniel]

I did not have the crank turned but I did use plastigage and I got a .002 reading on all the journals. I did not replace the oil pump but I did put it a bucket of oil and turn it with a drill and had good flow (good enough to shoot oil all over me) I also cleaned the screen and did an oil change then ran it for about half an hour and changed the oil again and filter. My oil pressure is usually 40 psi on the helm when I was in the water it was reading 40 but when I brought it game and put it on the muffs it was reading 40 then dropped to 20 about 5 min later and now reads 20.

 

[alldodge]

Spun 2 rod bearings and didn't have the crank turned, there was no scoring, and to beat that plastic gauged out at .002

I don't think so

Camshaft end play is .001-.009

 

[Bondo]

So I've been working on my 2001 4.3l carburated mercruiser with alpha 1 gen 2. Weve been in the river tubing and island hopping alot this year and the boat ran great. A few weeks ago on our way out from the dock I noticed it took longer to plane out and my rpms were lower than usual (4000 instead of 4500). So we got to the island everything seemed fine stayed there for an hour or so and loaded up to go tubing. The first riders got on and again slow to plane and lower than usual rpm. They were on for about 10 min then the next group got on and it wouldn't get on a plane and wouldn't go above 3000 rpm. So we went back to the dock. Looked up on the forum and decided to change plugs wires cap and rotor. Next day went out on a test run and still the same except there was a loud knock sounded like the motor was going to blow up. Checked the oil and it was barely on the dip stick so I pulled up to the bank added 3 quarts and proceeded idle back to the dock and the knocking never went away. When I changed the plugs cylinder 2 plug was blown out not crushed but the ceramic was gone from the tip. Long story short I pulled the motor replaced the rod bearings and pistons. Put it back together took ot out fo a test run and about 20 min in motor started knocking and shortly after it locked up. Pulled the motor again found cylinder 1 and 2 rod bearings spun j badly damaged. Pulled the crank shaft off and found the main thrust bearing was trashed. Replaced 2 rods rod bearings and main bearings. When I was putting everything back together I noticed the camshaft moving front to back. Took out for another test and now in getting a different knock checkech all my lifters they seemed fine. Now my question could the cam be moving forward and back be causing the knock. Or does anyone have any other sugestions?

Ayuh,...... Welcome Aboard,....... My guess is, yer killin' yer motor with Detonation, caused by a lean condition,.....

When it 1st was down on power, it was goin' lean,....
If you'd have changed the fuel filters, rather than the ignition, you mighta saved it,.....
The porcelain bein' gone on the plug was a big hint,....

Until you fix the fuel delivery system, it ain't gonna run Right,...

 

[Scott Danforth]

if you spun a rod bearing, not only do you need to either machine the crank or replace the crank, you need to either re-condition the rods or replace the rods.

however right now it looks like you need to replace whole motor and fix your fuel system

 

[TMcDaniel]

Ok so new motor is not an option. Now back to the cam shaft... there was definetly more than .009 of movement. Since a new motor is not an option tell me what you guys think about this... get crank turned and oversized bearings, replace oil pump new cam and cam bearings and 4 more rods. New fuel filter and find out why it's running lean.

would the fuel filter make it run lean or should I get the carb rebuilt?

 

[alldodge]

Fuel filter would not make it run lean, its the carb

As Scott said rods may be able to be reused but would need to be checked by a machine shop. I would take the short block to the machine shop and have them check everything

 

[achris]

Lean fuel killed the top end, overloading killed the bottom end.

When you pull anything with a boat, the load on the engine is disproportionately higher. Only pulling 4500 at WOT before you put anything behind the boat is an open invitation for rods and cranks to leave the building! And I would venture that even without towing anything, 4500 is too low.

So, when you get it all fixed up and sorted out, get into a smaller (pitch) prop... Prop that engine right to the top of the range (and 50 or 100 over isn't a bad thing).... Then once you have the right prop, buy a second prop 2" smaller again, and that's the one you use for pulling tubes and skiers.

Chris........

 

[TMcDaniel]

How can 4500 be too low when the manual says 4400-4800 for wot? And I've got 8 people in the boat so wouldn't 4500 be close enough to 4800 with 1400 pounds of people plus all our gear?

 

[Scott Danforth]

Ok so new motor is not an option. Now back to the cam shaft... there was definetly more than .009 of movement. Since a new motor is not an option tell me what you guys think about this... get crank turned and oversized bearings, replace oil pump new cam and cam bearings and 4 more rods. New fuel filter and find out why it's running lean.

would the fuel filter make it run lean or should I get the carb rebuilt?

why is a new motor not an option?

the detonation has lead to damaged bearings and pistons

get a price on getting the crank turned, then compare to a new out of the box crank. the new crank is usually cheaper.

same goes with rods

you still need to deal with the piston damage from detonation. so you either need to do a proper rebuild, or you need to replace

its running lean because your carb is dirty.

 

[achris]

How can 4500 be too low when the manual says 4400-4800 for wot? And I've got 8 people in the boat so wouldn't 4500 be close enough to 4800 with 1400 pounds of people plus all our gear?

I'm just passing on my experience as the owner of 2 of these 4.3 litre engines. Oh, and as a Mercruiser dealer who has PERSONALLY installed and propped dozens more.

Sorry to have bothered you...

Chris........

 

[alldodge]

How can 4500 be too low when the manual says 4400-4800 for wot? And I've got 8 people in the boat so wouldn't 4500 be close enough to 4800 with 1400 pounds of people plus all our gear?

If your normal running set up is as indicated then need to prop down. If your normal running is with less folks then your ok

Think of the prop like going up a steep hill in high gear, then motor would have an easier time pulling the hill in a lower gear. By propping down there is less strain. Your not going to burn more fuel with higher rpms because there is less HP needed to keep the speed, but would burn more fuel at lower rpm with a heaver load

 

[TMcDaniel]

Chris you have not bothered me I was simply asking a question. I'm not doubting anyones experience either, and I thank you for your input and I will be looking into a new prop. I was just confused of why 4500 rpm was too low. Thanks for the explanation alldodge.

I guess I'll be getting a short block and a new carb. Ohh yea and two new props.

 

[Searay205]

Did you hear any pinging or predentination when all this was going on? If it was that lean would the engine ping? Oh and if engine pings back off ASAP

 

[TMcDaniel]

I wouldn't say it was pinging... but there was alot of knocking. The sound I'm hearing now sounds like its coming from the top end. Is there any adjustment for the card besides the idle screw and the idle air? It's a two barrel mercard.

 

[Searay205]

I just surprised you can get it that lean and the boat run. Its not like a two stroke. Was there a ton of carbon buildup on valves? pinging, knocking is the mixture igniting before top dead center. theoretically. the mixture explosion is trying to push the piston back down while it still moving up. All fire BTDC but if to much knocking and pinging. if you had tons of carbon build up than changes the compression ratio and retains heat which can lead to predetination

 

[alldodge]

Carbon build up in excess will cause detonation, but we are all talking about lean fuel mix causing detonation. The fuel mix is so lean that it starts burning as the valve opens. This condition also causes back firing. Instead of plugs looking black and all carboned up, they are white and almost clean

 

[achris]

... I was just confused of why 4500 rpm was too low. ...

Maximum power from the 4.3 is at 4600rpm. The spec is 200rpm either side of max power. My experience, with all these V6s is that the bottom half of the rev range is to be avoided. As nice as they are, they don't have the low end torque of a V8. Once they are over about 3,200 they are fine, but in the 2,000 to 3,000 rev range they need 'help'. Help in the form of a lower pitch prop. By the book, mine (with the 4.3MPI) should be running 19", and with a 19" it runs to 4,600rpm. EXACTLY right, but it's not. In the mid range the boat feels sluggish and slow, and most of the time, I'm traveling in the 16 to 25 knot range, right where the shortcomings of the 19" prop are manifest. I put a 17" prop on and it's a whole different boat. The acceleration is really nice, the boat 'pulls' well, and it just feels more 'lively'. The boat is more driveably. And it was the same with the 4.3LX. 23" was right (engine had a 1.84:1 drive, as the 4.3MPI has 1.62:1), but was better with a 21".

And as by Merc recommendations, find the 'right' prop, then drop 2" if you intend towing a tube or skier. At one point I took my GF and her sons out for some tubing, and I only has a 15" prop (when I had the 4.3LX). It dropped 10 knots off the top end, but the pull and just how quickly it would turn stunned everybody, including me!

Simply rule with 4.3s. Find the 'right' prop, then go 2" shorter. THAT is the right prop. Want to go tubing (skiing), drop another 2" (at least)....

The shorter prop also reduces the load on the drive, and the engine. Everything lasts longer. An engine that can rev freely is a happy engine.

Oh, one more thing. Hear this from a lot of people too. 'The lower pitch prop (and thus a slightly higher revving engine) will use more fuel'. Couldn't be wronger! When I got the 4.3MPI in my boat I ran a series of prop tests. I ran a 17" 3blade, a 19" 3 blade, a 21" 3 blade and an 18" 4 blade. I was running rev and fuel flow tests. For the same boat speed, regardless of the prop, the fuel flow was the same. Yes, the revs were different, but the throttle setting to attain that speed was consistent. Bigger prop, lower revs, higher throttle opening. Smaller prop, higher revs, but less throttle opening (due to lighter load).

Chris..........

 

[TMcDaniel]

The motor is almost 20 years old but only has 190 hours on it. There was very little carbon on the valves however the spark plugs were white and "looked clean". I had a problem with vapor lock last year but I resolved that and it ran great until a few weeks ago. We usually go out one day every weekend sometimes 2 I probebly put 50 hours on it this year. I live in florida so weve been on the water since February.