mercruiser 140 3.0 timing gears

[Goldie627]

So after weeks of trials and errors, i think ive figured out my hesitation with acceleration problem. I can get up on plane, but, you have to move the throttle painfully slow to get there. anything other than a slow easy movement will cause a hesitation and/or stutter. a fast holeshot type acceleration command will cause the carb to backfire.

After two carb rebuilds (obsesssing over the accelerator pump), tune up, new fuel pump, verifying good fuel, verifying fuel pressure and installing electronic ignition with new distributer, i began to put two and two together.... actually scott mentioned it first and the more i looked at it the more it made since.

Thanks to rick stevens for turning me on to the vaccum gauge.

The low vacuum reading of 14, the way it hesitates and the tingy chattering sound that appears to be coming from the timing cover suggests that its the timing gears. on a slow easy acceleration the slop in the timing gears isnt very noticeable but when you accelerate normally or fast the slop in the gears is very noticeable causeing hesiation and/or carb pops.

Could you guys please watch the video and tell me if you agree?
you can really hear the chattering when i zoom in on the timing cover...

compression 1) 155 2) 165 3) 170 4) 175

timing 8btdc

vacuum from manifold 14

fuel pump pressure 5

carb rebuilt twice, double checking all specs

distributer Ignition Kit (sierra [FONT=&quot]18-5518)[/FONT]

 

[Goldie627]

hello all, I don't want to double post so I'm asking anyone who is interested to please go to

http://forums.iboats.com/forum/boat-...=1508456866122

and check out post #1176

I'm not sure but I think it's frowned on to double post, plus I'm trying to keep all my boat info in one thread...

Thank you all!

Mod Edit - Post #1176 is below.

Goldie - You can always start a new thread for something like this. In fact we encourage this. So for example, motor questions aren't lost in a resto thread.

 

[Goldie627]

Thank you GA, i wasn't sure on proper etiquette for this but moving forward ill keep all my engine repair posts in this section of the forum

 

[Goldie627]

so I visited a local marine mechanic this morning, he stated that it's rare for the gears to go bad on my 140 3.0 and that if the gears were bad my timing mark on the pulley would probably be moving all over on me when I had a the timing light on it, my mark is pretty steady with the light on it

He also states that the low vacuum reading could be an air leak somewhere around the intake manifold or base of the carb and to check that before taking the motor out

He also said I could try to adjust the timing by the vacuum gauge then adjust the carb to bring the idle down. then as long as it doesn't ping or knock under load should be ok... if that solved the problem, if it didn't solve the problem then set the timing back by the timing light

He also suggested to remove the alternator belt to verify that the chattering noise is actually coming from the timing cover and not the pulley or alternator

The last thing he said was to try and get a viton ethonal resistant accelerator pump...

I'll be a busy tester come Saturday morning

 

[kenny nunez]

Remove the spark plugs and turn the engine by hand to #1 top dead and check if the timing marks on the balancer line up with the marks on the timing cover to be sure the balancer did not slip. 2xs on what your mechanic told you.

 

[Rick Stephens]

Pretty good article on how to evaluate your vacuum readings.
http://www.tuneruniversity.com/blog/...-vacuum-gauge/

I think a low reading is more likely rings than timing gear.... I think the 3.0 a straight gear set without a chain. Pretty solid setup if noisy. Could be an intake leak. Check it with carb cleaner. Spray the intake gasket all the wy around and listen for the engine to gain RPMs.

 

[fishrdan]

Agree with checking TDC, I've verified TDC timing mark on my 3.0L (140HP Mercruiser) by removing the plugs, tightening the alternator belt, placing a screw driver into #1 cylinder so it rocks as the piston goes up-down, then rocking the engine with a wrench on the alternator pulley nut. You can use a piston stop also, but the way I did it, it was very apparent that the timing mark was 100% dead on TDC. (Kind of cumbersome rocking the engine, holding the screw driver in the spark plug hole and watching the timing mark, all at the same time, but it was very apparent that timing mark was accurate.)

Get a mechanics stethoscope and pin-point the noise before tearing in the engine. I agree with the mechanic on the timing gears not going out, often. The symptoms are classic accelerator pump issues, have you disconnected the carb linkage and verified you get 2 healthy shots of gas from the boosters, (engine off) flip the throttle wide open and see if there are 2 streams of fuel. I rebuilt my carb once, then a couple weeks later it was stumbling, accelerator pump had swollen up and was sticking in the carb, carp parts... Replaced the accelerator pump and all was well again.

You can run the engine without the alternator belt to troubleshoot where the noise is coming from. I woudn't run it for a long time like that, minute or so, but the outdrive's water pump has enough flow to keep the engine full of water and exhaust cool.

Electronic ignition with a new distributor? What ignition/distributor did you install? EST or mechanical advance?

 

[Goldie627]

Remove the spark plugs and turn the engine by hand to #1 top dead and check if the timing marks on the balancer line up with the marks on the timing cover to be sure the balancer did not slip. 2xs on what your mechanic told you.

hey Kenny thanks for the heads up on TDC, about a month ago I Installed a new Sierra Ignition Kit (sierra [FONT=&quot]18-5518)[/FONT]. The following steps is what I did to find TDC:

1. took out all the spark plugs
2. hooked up a remote start button (fat red wire on starter and yellow wire on starter solenoid)
3. put my thumb over the #1 spark plug hole
4. tapped the start button (you can feel the air from the chamber sucking (downtroke) or blowing (up/compression stroke)
5. after a few rotations around you can pretty much tell how the compression stroke feels
6. after the big blast of air i was super close to the harmonic balancer and the timing tab being perfectly lined up
7. i put a big boy crescent wrench on the alternator pulley nut with my right hand
8. put my left hand on the pulley above the harmonic balancer
9. and then turned it very easily the inch or so it had to go to line up (belt has to be reasonably tight to do this)
10. i removed the old distributor
11 i installed the new distributer, lined up the rotor with #1 (front of engine)
12 i set the distributer down a few teeth early because as it slides down it will move to a new position slightly around from where you started
13 it took me two tries to get it lined up (rotar with #1 front of engine)
14 now for the gap thats at the bottom, i was getting impatient wiggling the distributer so i took it out and used a screwdriver to stick in the hole and turn the oil thingy a smidge so the distributer would seat all the way down

after this process its starts right up on the first try every time, even cold starts

I don't think it has "slipped" because its been doing this "hesitation with acceleration" ever since I float tested, that was before the new distributer

 

[Goldie627]

Pretty good article on how to evaluate your vacuum readings.
http://www.tuneruniversity.com/blog/...-vacuum-gauge/

I think a low reading is more likely rings than timing gear.... I think the 3.0 a straight gear set without a chain. Pretty solid setup if noisy. Could be an intake leak. Check it with carb cleaner. Spray the intake gasket all the wy around and listen for the engine to gain RPMs.

Hey rick! always a pleasure! I'm gonna check the intake gasket as well as the carb gasket 2maro morning and let ya know what happens. I may use starter fluid too, I heard it evaporates quicker. I got my rear carpet put down with the snards. I'll take some pics and post them in the resto thread.

 

[Goldie627]

Agree with checking TDC, I've verified TDC timing mark on my 3.0L (140HP Mercruiser) by removing the plugs, tightening the alternator belt, placing a screw driver into #1 cylinder so it rocks as the piston goes up-down, then rocking the engine with a wrench on the alternator pulley nut. You can use a piston stop also, but the way I did it, it was very apparent that the timing mark was 100% dead on TDC. (Kind of cumbersome rocking the engine, holding the screw driver in the spark plug hole and watching the timing mark, all at the same time, but it was very apparent that timing mark was accurate.)

Get a mechanics stethoscope and pin-point the noise before tearing in the engine. I agree with the mechanic on the timing gears not going out, often. The symptoms are classic accelerator pump issues, have you disconnected the carb linkage and verified you get 2 healthy shots of gas from the boosters, (engine off) flip the throttle wide open and see if there are 2 streams of fuel. I rebuilt my carb once, then a couple weeks later it was stumbling, accelerator pump had swollen up and was sticking in the carb, carp parts... Replaced the accelerator pump and all was well again.

You can run the engine without the alternator belt to troubleshoot where the noise is coming from. I woudn't run it for a long time like that, minute or so, but the outdrive's water pump has enough flow to keep the engine full of water and exhaust cool.

Electronic ignition with a new distributor? What ignition/distributor did you install? EST or mechanical advance?

• Hey Fish, I think I got TDC correctly, please check post #8
• I agree with you 100%, I'm trying to exhaust all my options before pulling the motor
• I'll look around for a stethoscope, maybe harbor freight or a used tool shop
• On the second rebuild of the carb I bench tested the accelerator pump circuit before I reassembled everything and it seemed fine, while moving the pump up and down I was able it get gas with and without the venturi... coincidentally, the marine mechanic said that the plunger on the new accelerator pumps is made of neoprene (I think that's what he said) and it expands in gas so it cant pump like it should, then if you take it out of gas it shrinks back down. I noticed that the pump does return slow but I have nothing to compare it to so I'm not sure if that slow return is normal or not, would make since if the plunger had expanded though. the mechanic said to look for a viton ethanol resistant accelerator pump. I got my kit from mikes carburetors and I'm going try to find out what type of pump they gave me.
• http://bpi.ebasicpower.com/shop/inde...de93c5869e6c16 I think Mallory makes this part for sierra, so far I'm happy with it, it always starts right up
• I'm going to try the stetho route before taking off the belt

http://www.harborfreight.com/mechanics-stethoscope-69913.html

 

[Goldie627]

I just checked where I bought the carb kit from and it states:

"Rebuild kit, made in the USA from high quality ethanol ready parts."

http://www.carburetor-parts.com/Mercarb-Carburetor-Kit_p_3483.html​

 

[Grub54891]

I know on my 3.0 it had the composite large gear on it. When I was going through the gaskets and seals I found it had some chips out of the teeth, Not so much to affect the gear, bit I replaced them with full metal gears anyway. It's still on the stand, I hope it's not noiser but we will see in the spring.....

 

[fishrdan]

Yes, that looks like a Mallory distributor, I was asking to make sure you didn't have EST ignition, different timing procedure.

Not that this is going mean much, but the bad accelerator pump I got had a black cup seal, it swelled up too much to work right. I put the old "blue" one back in the carb, and it worked perfect.

 

[mrpatel]

I have a similar issue. What did you find out to be the problem?