Crank endplay-Merc 305 chebby

[WizeOne]

Is there anything inherentin an I/O setup that would account for excessive crankshaft endplay? In this case, a Merc 1R.

My friend has, what appears to be a low mileage 305 that freeze broke. He is changing out the block and discovered that there was .030 endplay when he mock-assembled the crank into the new block. The book calls for .004-.006?

By all accounts this motor had no wear in it. The cylinders had no taper or ledge and all the bearings look good.

What possibly could account for this endplay? Or should he just write it off and install the new main bearings?

 

[Bondo]

Re: Crank endplay-Merc 305 chebby

Is there anything inherentin an I/O setup that would account for excessive crankshaft endplay? In this case, a Merc 1R.

Nope....

Your Bud needs to do whatever it takes to get the motor "In Spec" before he installs it,...
Or,...
He'll be doing it again,.. Soon...

 

[mtnrat]

Re: Crank endplay-Merc 305 chebby

If you are in there already install all new mains.
Are you sure you are checking it correctly. Here is what I do.
In my opinion an accurate method of checking crankshaft endplay is to mount a dial indicator using a magnetic base on the block. The endplay is how far the crankshaft moves in the fore/aft direction within the block. After you align the thrust bearings push the crankshaft all the way forward and zero your dial indicator, then push it rearward and read the dial which will be your endplay. You can use feeler gages and many people do sucessfully but I prefer to use a dial indicator. Hope this helps!
I borrowed this method from a post in another forum from when I built my engine.

 

[Don S]

Re: Crank endplay-Merc 305 chebby

Does he have the correct rear main bearings in there, the ones with the thrust bearings on each side? if so, then he needs a new crankshaft.
PS: What year is this engine?

 

[WizeOne]

Re: Crank endplay-Merc 305 chebby

Does he have the correct rear main bearings in there, the ones with the thrust bearings on each side? if so, then he needs a new crankshaft.
PS: What year is this engine?

Don, the engine may be (or was) a 1978. I'm not sure if it was a replacement motor or just a low mileage original motor, from all other indications. I'm also not sure the vintage of the new block.

I know he is using a magnetic dial indicator to measure the endplay. He is a pretty accomplished mechanic.

Do rear main bearings come with or without thrust bearings on each side? I'll check with him to see what he has. This mid morning he was getting ready to set the crank with the new bearing set. He would then recheck the endplay.

 

[WizeOne]

Re: Crank endplay-Merc 305 chebby

Ok, he set the crank with the new bearing set. The endplay is now within spec.

He stated that the old bearings look pristine except for the visually noticable wear on the forward thrust surface of the rear main bearing. He stated it was as if something was constantly putting forward pressure on the flywheel.

He's never seen that kind of wear in an automotive application and that is why he wondered if there was something inherent in an I/O marine application that would have caused this.

 

[mtnrat]

Re: Crank endplay-Merc 305 chebby

If anything a marine application has little chance to put pressure on the thrust bearing. In an auto the torque converter and tranny can add alot of pressure if not set up correctly.