Pistons bottom out

[Josedcr]

I?m reassembling my V4 140h 1978 Evinrude. I installed the pistons and crankshaft but the shaft would not do a full revolution. I temp installed the shaft bearings and the crank cover (to center the shaft) and it still will not do a full turn. I noticed that the 2 port side pistons bottom out and that is not allowing the rods to over-center (both directions) and the crankshaft can?t make it around. This was a running motor that busted a piston ring and that?s why I?m rebuilding. The skirt in 3 of the pistons were cracked, so I imagine they were hitting before. The motor has been worked on before I got it.

What can be the problem?

 

[boobie]

Re: Pistons bottom out

What did you all replace when you did the rebuild ? Did this mtr run when you got it ?

 

[Dhadley]

Re: Pistons bottom out

Were the cylinders bored?

Are you sure the block is a 1978?

 

[jeffersondodson561]

Re: Pistons bottom out

Did you put the pisons in the correct way "arrow facing the exhaust" side?

 

[Josedcr]

Re: Pistons bottom out

The engine ran ok for a while. The lower carb got plugged and the engine ran without lubrication on the lower two pistons which locked the lower left piston rod (at the piston) and the piston rings snapped. I had the cilinder bored and bought a new oversized piston and 2 used regular pistons to replaced the cracked ones. The engine had parts from different motors (bought it like that), but it ran ok...

 

[Josedcr]

Re: Pistons bottom out

I did put the pistons in the right way...

 

[58rude]

Re: Pistons bottom out

Sounds like the wrong parts. Piston skirt is too long or the crank has too much stroke. I am leaning towards wrong pistons, too much stroke would cause the piston to hit the head, maybe. Could be the wrong rods also. If the rods are too short, it would cause this also. The piston skirt length may be the same and the wrist pin location might be slightly lower. You need to match everything up to old parts etc. Good luck.

 

[Dhadley]

Re: Pistons bottom out

OK, are the 2 cylinders you had bored the same ones that the pistons bottom out in?

 

[Joe Reeves]

Re: Pistons bottom out

You say that you've temporarily installed the forward crankcase half to keep the crankshaft centered.

I suspect that you do not have the center main bearing seating hole set properly so that it locks into the centering pin properly. This would cause the crankshaft to be forward further than it should which in turn would cause to pistons to bottom out on the bottom of the throw.

The proper method of assembly is to have the top and bottom crankcase heads (crankshaft heads) installed to hold the crankshaft in place, leaving the forward crankcase half to be installed later..... normally impossible to bolt those two heads up if the center main bearing isn't seated properly.

 

[Faztbullet]

Re: Pistons bottom out

I tend to agree with Joe as crank not seated. If it is seated then you got: A) wrong pistons or B)Motor is a 135 not a 140..The piston should measure .800 from bottom of wrist pin to bottom of skirt for a 140 and a 135 measures .660

 

[emdsapmgr]

Re: Pistons bottom out

Visually compare all the pistons you have in the engine. Specifically, look at the location of the piston pin in the piston. OMC changed that pin height (location) at one point, and had to change the length of the rod at the same time. If you have pistons from an older engine running on your current rods, you can have problems with the total overall length of that assembly. The piston/rod change was made somewhere in the 72-73 timeframe. I'd check the part numbers of pistons and rods and compare them to various OMC parts lists to see what you have. You may be able to run those older pistons, but you'd have to use the rods that match.

 

[Josedcr]

Re: Pistons bottom out

I tend to agree with Joe as crank not seated. If it is seated then you got: A) wrong pistons or B)Motor is a 135 not a 140..The piston should measure .800 from bottom of wrist pin to bottom of skirt for a 140 and a 135 measures .660

I checked the center bearing and Joe was right about it not being seated. I set it correctly but the pistons are still hitting. I'm removing all of it and making sure the parts are the right ones...

 

[seahorse5]

Re: Pistons bottom out

I've seen the same thing quite a few times, usually from a place who is not familiar with boring outboard cylinders. Very often the machinist does not run the cutter bit far enough down the cylinder bore and into the aluminum. This is assuming that the parts and assembly procedures are correct.

 

[nymack66]

Re: Pistons bottom out

I've seen the same thing quite a few times, usually from a place who is not familiar with boring outboard cylinders. Very often the machinist does not run the cutter bit far enough down the cylinder bore and into the aluminum. This is assuming that the parts and assembly procedures are correct.

Correct, A special machine is needed to bore (blind hole) if not the ridge left will create the issue posted ...

 

[Josedcr]

Re: Pistons bottom out

Visually compare all the pistons you have in the engine. Specifically, look at the location of the piston pin in the piston. OMC changed that pin height (location) at one point, and had to change the length of the rod at the same time. If you have pistons from an older engine running on your current rods, you can have problems with the total overall length of that assembly. The piston/rod change was made somewhere in the 72-73 timeframe. I'd check the part numbers of pistons and rods and compare them to various OMC parts lists to see what you have. You may be able to run those older pistons, but you'd have to use the rods that match.

I took all of it out, and compared the pistons. I had bought a brand new oversized piston for the cilinder I had bored. I bought 2 used pistons (from a 140h 1979) to replace the cracked ones I found. I compared those 3 pistons and they are all the same legth from skirt to wrist pin. The one piston I didn't replace is shorter from skirt to wrist pin.

Mi engine is a 140h 1978 cossflow (according to the freeze plug), some of the parts came from older engines and probably different horsepower. I believe that the pistons and rods used in it are from the older version with shorter skirt and shorter rods. I guess this means that the newer pistons need a longer rod. Am I correct?

 

[58rude]

Re: Pistons bottom out

Sounds like you figured it out. Need to get the specs on the parts and see if they match.

 

[emdsapmgr]

Re: Pistons bottom out

You might want to replace that 4th piston/rod so that the pistons and rods all match. OMC tries to insure that all pistons in an engine weigh the same. Don't know for sure if pistons from a different vintage (different pin location) will weigh the same. You can order a replacement part number piston/rod from the original parts list, and OMC will give you the correct replacment. Or find a used one with a rod. Also-check out the cross-section of the rings. Some of the older pistons have regular rectangular cross-section rings. The newer ones have the pressure back rings, that are "V" shaped-a really nice (engineering improvement) feature. You really want them to match.

 

[Josedcr]

Re: Pistons bottom out

You might want to replace that 4th piston/rod so that the pistons and rods all match. OMC tries to insure that all pistons in an engine weigh the same. Don't know for sure if pistons from a different vintage (different pin location) will weigh the same. You can order a replacement part number piston/rod from the original parts list, and OMC will give you the correct replacment. Or find a used one with a rod. Also-check out the cross-section of the rings. Some of the older pistons have regular rectangular cross-section rings. The newer ones have the pressure back rings, that are "V" shaped-a really nice (engineering improvement) feature. You really want them to match.

That was my plan; to replace the 4th pistom with one that matches. The pistons I'm keeping do have the "V" shape cross-section rings. I can get a set of rods with a casting # 321712. Would anyone know if these will work or were to find a casting/part list compatibility? The evinrude website only gives me part numbers...

 

[emdsapmgr]

Re: Pistons bottom out

Hard to tell exactly what your part number equates to. I've had luck calling the Bombardier Consumer Hotline, here in nearby Waukegan. Give them a try on Monday: 1-847-689-7030. They are usually very helpful.

 

[Josedcr]

Re: Pistons bottom out

You say that you've temporarily installed the forward crankcase half to keep the crankshaft centered.

I suspect that you do not have the center main bearing seating hole set properly so that it locks into the centering pin properly. This would cause the crankshaft to be forward further than it should which in turn would cause to pistons to bottom out on the bottom of the throw.

The proper method of assembly is to have the top and bottom crankcase heads (crankshaft heads) installed to hold the crankshaft in place, leaving the forward crankcase half to be installed later..... normally impossible to bolt those two heads up if the center main bearing isn't seated properly.

Joe,

I got the pin aligned but my connecting rods are not the correct part #. I got a set of rods with a casting # 321712, but they are to big (radius) where they connect to the crank. I can't figure out what part/casting # I need since some have the 321712 listed as usable on the 1978 140h evinrude. Do you know or would anyone know were to find the right rods for my motor?