Piston Replacement Merc 140 4cyl

[Strait 4]

Have to remove #4 piston to inspect for a possible pinched ring. Exhaust valve seat failed resulting in contact between piston and cylinder head. Damage to top of piston is minor, but it is located on the edge-above ring. No scoring to cylinder wall.

Do not want to remove engine if possible. Can drop the oil pan only 2" under #1 cylinder-bilge area. Not sure (oil pump pickup) if I can then tilt the pan enough to get a wrench under #4 to remove the connecting rod nuts and bearing cap. Then have to figure out what to insert to push piston out top.

Has any one done this or have any suggestion? Thank you, Doug

 

[Kainon]

Re: Piston Replacement Merc 140 4cyl

put the #4 at the bottom of the stroke, drop the pan, remove the con rod cap, rotate back to top of stroke, add multiple rachet extensions together, tap from below, once you get the top ring out, should have enough to get the rest of the way,

When reinstalling, have the crank at the bottom of the stroke and put protectors on the ROD Bolts.

 

[Strait 4]

Re: Piston Replacement Merc 140 4cyl

Thank you Kainon for the quick reply and will give it a try.

This forum has been very helpful keeping this older boat running, Doug.

 

[Silvertip]

Re: Piston Replacement Merc 140 4cyl

I'm betting that removal of the engine would actually save you time and frustration.

 

[Bondo]

Re: Piston Replacement Merc 140 4cyl

I'm betting that removal of the engine would actually save you time and frustration.

Ayuh,.... No doubt about it...

 

[zbnutcase]

Re: Piston Replacement Merc 140 4cyl

And how do you plan on gettin a torque wrench in there????

 

[dingdongs]

Re: Piston Replacement Merc 140 4cyl

obviously the head is already off so for the sake of pulling the drive and a few extra bolts you can save yourself a lot of heartache and be left with your knuckles to do the piston pulling the correct way.a couple of burly guys could possibly lift engine so you can do all work on floor of the boat.keep everything labelled up to know what come from where.unfortunately a boat is not like a car so engine has to be removed.

 

[Strait 4]

Re: Piston Replacement Merc 140 4cyl

Dropped the oil pan this morning. Based on the prior responses, I was not overly surprised to find that there was not enough clearance to properly access the connecting rod cap nuts. Therefore, will have to do it the right way and pull the motor. Fortunately, the engine removal will not be that much more work as most everything on and around the motor has already been removed. With the engine out, I will also consider replacing the rear main seal and engine mounts for preventative maintenance.

The boat is a 17? 72 Larson and has a 6? beam. Do not have access to a gantry. Therefore, will remove the interior seats and place a ?? sheet of plywood on the bottom of the boat. Will rent-use a standard auto engine hoist and will have to construct some sort of engine support as the piston repairs will be completed in the boat. Still not certain that there is any damage to the piston ring, but at least I will have peace of mind!

 

[Strait 4]

Re: Piston Replacement Merc 140 4cyl

Repair update:

Reviewed repair manuals (online and book) and supplemented with iboat forms. Discovered that pulling and re installing a marine engine is a little more involved and not as obvious as an auto. This is because the outdrive MUST also be removed. I agonized over this substantial additional effort given the seemingly minor damage to the piston top and no scoring of the cylinder wall. However, the quote from Moderator Don S, ?Why is there never enough time to do it right the first time, But always enough time to do it again? kept me going. Also read on other auto forums how only the upper end of similar damaged engines were rebuilt and later failed.

A local boat repair shop quoted approx. $1,200 to address the one piston only and I would re assemble the rest! Already out $600 for the head rebuild, gaskets, hoses and cleaning supplies.

This forum has been invaluable and has given me the confidence to continue! I built a wooden outdrive stand with casters, based on designs in the ? MUST HAVE Technical Information for DIYers?. It worked great! Pulled the outdrive easily and have ordered the alignment tool for the re-install.

Pulled the engine today and removed the damaged piston. Turned out the top compression ring was pinched! The soft aluminum piston is no match for a cast iron head and valve seat! Who knows how long the engine would have run, before the ring broke and cylinder wall ruined. Based on my experience and others, the piston has to be pulled and inspected if there is any damage around the edges.

 

[bigskiohio]

Re: Piston Replacement Merc 140 4cyl

pulling a mercruiser outdrive takes 10 minutes. engine 1 hr.

 

[fat fanny]

Re: Piston Replacement Merc 140 4cyl

Man if you have gone that far go all the way nows your chance hone, re-ring, bearings, check cam and crank, seals and oil pump why do all that work and possibly have to go back later (god forbid) and do it again. Good luck!

 

[Strait 4]

Re: Piston Replacement Merc 140 4cyl

Update:

Just finished the 1st 4 hrs on the water of the 20 hr recommended break-in on the rebuilt motor. No problems, leaks or adjustments! Engine was started 1st time yesterday. Fired the first time and ran strong.
Only needed to adjust-fine tune timing, re-torqued head and adjusted lash lifters before on water break in. Also changed oil and filter-cheap insurance.

Ended up having head re-built-valve job, replaced 1 piston, tappet and push rod. Re-ringed and replace rod bearings remaining pistons. Also used 240 grit ball hone all bores. Motor only has approx. 700 original hours and was running strong prior to the valve seat failure. Therefore, further rebuild was not required.

Observations:

This web site was critical to the success and substantially reduced the learning curve on the project!

Suggestions:

Currently using the break in procedures listed in this site as they are marine specific.

http://forums.iboats.com/showthread.php?t=248452

Outdrive removal and install-required engine removal:
Made a stand with wheels and purchased an alignment tool on Amazon as suggested on this site. Pulling the drive is no problem. The stand and tool are required-helpful for the re-install. Only took ? hrs and that was because I had to re-pull the drive as a washer was left on the bell housing! Too many things to line up (U joint spline, shift arm and shifter foot) and this is where the stand pays off. Proper alignment of the gimbal bearing is obvious.

http://forums.iboats.com/showthread.php?t=420930&highlight=install+outdrive

Oil pan:
Marine oil pan gaskets are very expensive. 1 piece silicon is approx $80 while the less expensive 4 piece cork was still $50! I used the 4 piece cork and did a lot of research on this. Straightened pan flanges and flattened minor dimples. Lightly used a flat file to confirm level. Used old school Indian Head gasket shellac on the cork sections to pan-let dry overnight. This keeps the gasket from moving during install. Black Permatex in the 4 corners-rubber to cork. Also added a thin layer of wheel bearing grease on cork -block side-non Sealer sections. The grease causes the cork to swell and results in a better bonding surface.

Recommend pan bolt torque specs in Cylmers and Merc Serv Tech manual #13 appear to be for new silicon gasket with metal spacers! Set my ? torque wrench to above specs and watched my cork gasket deform very quickly. Re adjusted to 20 inch lbs as this was the minimum setting on my wrench. This still produced minor deformation but was acceptable. The key is to adjust the torque wrench to your cork gasket-not just to specs. Also used a criss- cross tightening pattern. The above resulted in a 1 time install with no leaks and no adjustments.

Hope this helps , Doug.

 

[Aloysius]

Re: Piston Replacement Merc 140 4cyl

Congrats! you did it the correct way!

 

[Eric 3.7LX Alpha 1]

Re: Piston Replacement Merc 140 4cyl

Always good to hear a boat back in the water running well after a repair like that.