Mercruiser 140 Timing Gear Replacement

[sailor1]

I have a 1982 Sea Ray with a Mercruiser 140 I/O, engine SN 6045398 and outdrive SN 6039139. With light use in fresh water and regular maintenance, I have had no serious problems until now.

The engine developed a knocking sound and I only ran it a few minutes to get back to the dock and it had good oil pressure while it ran. I started it again and pulled each plug lead to see if it was a rod or pin noise but no change. It then stalled and when I cranked it over, it went a few turns before locking up. The cylinders were full of water, it had no compression when tested (after draining the water) and the distributor rotor is about 20 degrees retarded from where it should be. Conclusion is that the timing gears are out of mesh and maybe the knocking noise was caused by that.

I am planning to pull the timing cover off and see what I have. If I am lucky, the damage will be confined to one or both gears and not have damaged the keyway on either shaft. If I am not so lucky, I guess the engine will have to come out for a complete replacement or rebuild.

Assuming I get that far, I have looked at the procedures in the manual for replacing the vibration damper and read a number of earlier posts on this forum about the procedures for doing so. My engine does not appear to have a threaded bore in the center of the crankshaft. The manual I have is for a later 3.0 version of this engine and it shows a tool for installing the damper that threads into the center of the crank. However it also says an alternative method is to tap it on using a block of wood.

A number of posts I have read say the best way to avoid damage to the thrust bearing is to remove the engine. Does that mean that you need to put the entire engine block with the crank installed in a press? If you use the block of wood method and clean up the crank and damper bore carefully, can you avoid damaging the thrust bearing?

Appreciate any advice anyone can offer

 

[djvan]

Re: Mercruiser 140 Timing Gear Replacement

When I replaced my timing gears on the same engine I removed the engine and stood it on it's rear, to support the aft end of the crank. This will require you to remove the bell housing (the piece that covers the coupler). Then installed the damper. I had to remove the engine anyway because the cam with the gear installed wouldn't go in without hitting the floor. I just installed with a hammer and a block of wood. Right or wrong I don't know. I replaced the fiber gear with an automotive set (I think for a 1964 Cevy II) all aluminum and didn't notice a difference in noise.

The gears should be replced as a set.

I can't remember for sure if my crank is threaded or not.

I may have been able to istall the balancer with a bolt but had to drive the crank gear on.


HTH"s

DougV>

 

[sailor1]

Re: Mercruiser 140 Timing Gear Replacement

Doug V:

Thanks for the info.

I believe that I can remove the cam without removing the engine. Since I will need to replace both gears as a set, it sounds like you used a hammer and wood block to tap the crank gear on as well as the vibration damper. This is consistent with what my manual shows, but they also call it a "sprocket" and talk about a timing chain which this engine does not have.

I would assume the concern about damaging the thrust bearing would be the same as for putting the vibration damper on that way. Since I want to try this without removing the engine, did you find that you had to hit the gear or the damper really hard or were you able to tap it reasonably gently?

Thanks in advance.

 

[djvan]

Re: Mercruiser 140 Timing Gear Replacement

Had to hit it pretty hard. I didn't want to risk damaging the thrust bearing. I had my egine out anyway since the cam gear hit the floor. As much as you don't want to hear it I would take the engine out for this. Probalby big $$$ if you damage the bearings.

DougV>

 

[Bondo]

Re: Mercruiser 140 Timing Gear Replacement

Since I want to try this without removing the engine,

Ayuh,.... I wouldn't even Think of Trying it.......

The Oil Pan goes on After the Timing Cover,....
With the motor In the boat,....
You'll Never get it sealed up right,+ Always have an Oil Leak....
And,...
I Agree with djvan,...
You'll Trash the thrust bearing if you don't support the tailend of the Crankshaft.....

This isn't the place to be Cutting Corners........

 

[sailor1]

Re: Mercruiser 140 Timing Gear Replacement

Dear all:

Here is an update on my timing gear diagnosis. I have now pulled the vibration damper and removed the timing cover and confirmed that the fiber timing gear is missing several teeth. I have two questions for the group:

1. would the knocking noise I heard before the engine quit running be caused by one tooth starting to go bad before it let go and stripped several other teeth? (remember I always had good oil pressure and pulling each spark lead did not change the noise and with the cam out of position the engine turns over easily by hand suggesting the valves are not hitting the pistons)

2. A local mechanic suggested that I can drill and tap the crank where a vibration damper bolt would normally go and use a proper installation tool without pulling the engine. I see in the later year manuals for the GM 181 mercruiser engines that they do use a bolt to hold the vibration damper on. Does anyone know the thread size of that bolt?

Thanks for the help so far.

 

[Bondo]

Re: Mercruiser 140 Timing Gear Replacement

2. A local mechanic suggested that I can drill and tap the crank where a vibration damper bolt would normally go and use a proper installation tool without pulling the engine. I see in the later year manuals for the GM 181 mercruiser engines that they do use a bolt to hold the vibration damper on. Does anyone know the thread size of that bolt?

Ayuh,....

Doing what Should be done in a Machine Shop,.. In the Boat,..??..??

I'd think your odds of getting it Straight,+ True to be about Nil....

And,.. While it's been awhile since I've had 1 in my hand,...
I believe it's either 1/2" or 5/8", Fine thread....

 

[JustJason]

Re: Mercruiser 140 Timing Gear Replacement

Doing what Should be done in a Machine Shop,.. In the Boat,..??..??

Yep.... and on top of that..... there's no way your going to drill into a crankshaft with your cordless black and decker and some home depot drill bits......

just ain't gonna happen

 

[chiefalen]

Re: Mercruiser 140 Timing Gear Replacement

Why was it full of water?

 

[sailor1]

Re: Mercruiser 140 Timing Gear Replacement

It was full of water because once the timing gear stripped the cam was about 20 degrees or more retarded from where it should have been and the exhaust valves were still open when the piston started down on the intake stroke. This created a vacuum in the exhaust manifold and sucked in the cooling water that was supposed to go out with the exhaust.

As for the other replies relative to drilling the crankshaft, I agree that getting it straight is a challenge. However there is a 3/8" pilot hole in the end of the crank from the machining process. If I decide to try this, I will start with a drill of the same diameter and see if I can deepen this hole to about 1/2". And for what it is worth, I would use a real 1/2" drill and machine shop drills of the same material (probably high speed tungsten steel) use to cross drill crankshaft oil galleries. However, I have taken all the advice seriously and expect that most likely I will pull the engine now that I have the boat out of the water and back in the garage.

 

[sailor1]

Re: Mercruiser 140 Timing Gear Replacement

I have now finished the repair and owe you all an update in exchange for the good advice. I also consulted with the local engine rebuilder who pressed my new cam gear on the cam for me and his advice was to drill the crankshaft rather than using a hammer to install the vibration damper whether the engine was in the boat or not. His explanation was that even with the engine standing on end and the end of the crank taking the thrust there was a possibility of bending the crankshaft.

He also said that the crank was pretty soft in the center and that it could be drilled easily as long as I went up 1/64 at a time. Since my engine sits above the floor of the boat, I was able to level the top of the engine and then level the drill on support blocks and used a square to line it up side to side. In short it worked and I ended up with a 3/4" deep 7/16 course tapped hole that fit the installer adapter.

So the the new cam gear is in, and the engine reassembled and running. The only thing that I found was that I could not adjust the valves the way the manual says. I installed new hydraulic lifters but when I adjusted the valves to remove all lash, I had no compression. When I loosened them up to have about .005" lash like it was when I took it apart, I got the compression back and everything worked fine with no lifter noise as I had before with the old lifters when they were cold.

Thanks to all on the forum who helped me avoid doing damage with a hammer!

 

[sailor1]

I happened to see a very old message on iboats asking where I got the timing gear set (from the local machine shop that pressed on the new cam gear) and I looked up the original post to confirm that this was 12 years ago! I thought I would let the forum know that I still have this 28 year old sea ray and it continues to run well with routine maintenance, no other major repairs since the timing gear and valve lifter replacement. I suspect that being a fresh water boat that is stored inside for the winter probably contributes to it's long life. I am glad that I followed the advice of the forum to not hammer the vibration damper back on and opted to drill and tap the crankshaft so I could use an installer tool.

 

[Bondo]

I happened to see a very old message on iboats asking where I got the timing gear set (from the local machine shop that pressed on the new cam gear) and I looked up the original post to confirm that this was 12 years ago! I thought I would let the forum know that I still have this 28 year old sea ray and it continues to run well with routine maintenance, no other major repairs since the timing gear and valve lifter replacement. I suspect that being a fresh water boat that is stored inside for the winter probably contributes to it's long life. I am glad that I followed the advice of the forum to not hammer the vibration damper back on and opted to drill and tap the crankshaft so I could use an installer tool.

Ayuh,........ Thank you Sailor1,...... That's what I call an Up-date,........ 'n We Love Up-dates here at iboats,.....