1978 90HP inline 6 Rebuild, older post?

I have been looking for older post on rebuilding an inline 6 90HP mercury 1978 model. I am at the point where I am installing the crank and pistons. I read a post about inserting the pistons first and then connect them to the crankshaft. I ran into trouble here. I'd like to get an explanation on where the crank needs to be positioned when attaching the rods in that manner. I could not get the crank to turn a full rotation when I tried it the first time. Two of the rods would not turn easily on the crankshaft. If someone could steer me in the direction of an older post on this or perhaps guide me through this? That would be great. Thank you in advance.

Re: 1978 90HP inline 6 Rebuild, older post?

I can't lead you to the older post you are seeking. But it has been my experience rebuilding auto engines and small motors, that if the connecting rod doesn't turn easily on the crankshaft. It is a very good possibility that the connecting rod cap is installed backwards. If you are using the same caps that came off the crankshaft, they are worn to each other. I would try turning the caps and see what that does, plus check the torque. Could have possibly overtightened them.

Re: 1978 90HP inline 6 Rebuild, older post?

Thanks Crazyman, I had just finished reading about that in the repair manual. I believe you are correct I did not look to see if I had set them back in the correct direction they were removed. This may seem like a dumb question but is it possible to install the rods like say on the opposite side of the crank or upside down I guess? I ask because it seemed like some of the pistons were coming up to high and may hit the crank with the piston skirt. I'm certain I had the crank seated properly on the block and all pins lined up, so I'm just wondering if Maybe I connected some of the rods incorrectly on the crank. Your help is greatly appreciated.

Re: 1978 90HP inline 6 Rebuild, older post?

This is not intended to make you look stupid my friend. But when tearing down a motor with more than one cylinder, usually the pistons and other related parts are laid out in sequential order that they come out of the motor. Example, #1 piston, 1st piston in line, #2 piston, 2nd in line, #3 piston is 3rd in line. I usually lay out the parts from left to right. Sometimes it even helps to lay stuff on a piece of cardboard and mark it with a marker, #1, #2, #3, etc. etc. If you have the connecting rod hooked to the piston skirt correctly, and the crank shaft is seated correctly, the piston skirt should not touch the crankshaft. They will come close, but shouldn't touch it. The problem sounds like something isn't seated properly, or you have the connecting rod caps installed incorrectly, or possibly you have your pistons installed out of order so they aren't matching the crankshaft. Or the last possibility is that even the piston is installed incorrectly. By that I mean it needs to be turned 180 degrees on the crankshaft. One side of a connecting rod can wear more than the other side, so when installed incorrectly it will cause binding. Once the motor is assembled at the factory when new, the connecting rod journal and the crankshaft start seating themselves while the motor is run. If these pieces are not reinstalled back the way they were taken apart, it is like trying to put a square peg in a round hole. It can create a major headache.

Re: 1978 90HP inline 6 Rebuild, older post?

Bill, The pistons will only fit into the cylinders one way, due to deflector on the top of the piston. Normally when you disassemble, you put the roller bearings into numbered cups, and reinstall the rod caps onto the rods, so they do not get mixed up.

There should be scribed marks on the rod caps to match them to the rods.

Put all the pistons into the bores, and push them all down. Now lay the crank on the block and pull the #1 rod up a bit. Smear some heavy grease on the rod, and install the cage and bearings. Now pull the rod up to mate with the crank. More grease, cage and bearings, and then the rod cap and bolts. If that motor has the rod bolts and nylon lock nuts, you may reuse them. If it has just the rod bolts into threaded rods, replace them.

Repeat with piston #2 and then the others. Rotate the crank as necessary.

Re: 1978 90HP inline 6 Rebuild, older post?

Thanks for the replies, I have kept all the rods and bearings in order, none have them have been mixed up with each other and the pistons and rods are all back in their original cylinders, the problem on my first try I think was that I had tried to connect the rods while I had the crankshaft elevated on a hoist and at the same time trying to keep the rings in the cylinders. Also I did not have the rod caps attached in order with the rod. So I will try to attach them they way Chirs1965 stated. I have done cylinder 1 so far and it seems to be going much smoother. I am just a little concerned about not being able to torque them. Any idea?s on that? Thank you both very much for your help.

Re: 1978 90HP inline 6 Rebuild, older post?

Little update: I discovered the reason the crank would not turn on my previous attempt to install the pistons, it was the end cap Assembly's that were not installed in the correct position. Like the middle bearings the end cap Assembly's also have that recessed area that needs to be installed correctly so that the piston skirts do not hit them. Mystery solved. anyway now I have all the pistons and the crank installed and moving freely as it should, all looks well so far. except I noticed one of the oil seals inside the lower end cap is torn. Just one thing after another.

Re: 1978 90HP inline 6 Rebuild, older post?

That's a tough break finding the torn seal after all the installation of everything. Doesn't it seem like that is the way it always goes? Just when you think you made three steps ahead, something pops up and sets you back five. You are welcome for the advice. I'm not an ASE Certified mechanic, but will share what I do know to be factual. Always remember, a motor is a motor, it's a lot of the add ons that make things confusing.

Re: 1978 90HP inline 6 Rebuild, older post?

If you dont torque them connecting rod nuts it wont live... that model does not have cracked rod caps so you need the ring installers and you install the crank with piston and rods attached.

Re: 1978 90HP inline 6 Rebuild, older post?

Bill, You should be able to remove the bottom end cap, without disassembling anything. Put three new seals in the end cap, and inspect the end of the crank for grooves and burrs. Oil up the seals before installing the end camp, and use a new oring on the end cap.

Re: 1978 90HP inline 6 Rebuild, older post?

I do not have access to the ring compressors and they would run another two hundred or so to buy, so I went ahead and installed the pistons and crank as Chris suggested. Because I could not get my torque wrench on them I tightened them as much as I felt comfortable without over tightening using a 1/4" ratchet. I also used red thread lock (the nuts are the ones with nylon) so cross my fingers and see what happens. I got the seals in today also but I did not read in the repair manual if I needed to put any amount of oil in them before putting it back. Do I need to add oil in-between the seals? I used green thread lock on the outside edges as the manual suggested to help keep them in place I guess, that is where I stopped for today. I'm planning on finishing it tomorrow but I?m going to rebuild the water pump before I attach the power head back on the lower unit so that may be a few more days before I get the chance to do that. And as always thank you all for your help.
P.S. Chris you said put three new seals in the lower end cap. It had only two in it and I placed the new ones exactly as they were removed. Should I have added a third?

Re: 1978 90HP inline 6 Rebuild, older post?

Another question. I noticed in the manual there should be 2 end cap to crankcase shims originally installed. I don't have these shims in the old parts and there is not any new one's included in my gasket and O-rings set. I did measure the places the manual said to measure for end play and it seemed OK, but I could be wrong. There is very little play in it. Do I need to add these shims? and do all inline six models have these?

Re: 1978 90HP inline 6 Rebuild, older post?

Bill, Two seals in the end cap seems to be normal out of the factory. A rebuild PH I bought had three seals, so they will fit. The oil is just to allow the crank to slide thru the seals w/o tearing them.

My IL sixes only had brass shims on the upper end cap. the lower cap had no shims...

Re: 1978 90HP inline 6 Rebuild, older post?

OK thanks Chris, You have been very helpful. So far everything looks good. If you haven't noticed by now this is my very first rebuild of any engine and I don't really expect it to work but if by some miracle it does I will just be pleasantly surprised. Thanks again.

Re: 1978 90HP inline 6 Rebuild, older post?

Just wanted to give an update and some closure. I got the timing set and the carbs in sync today and took the boat out on the water. Spent about three hours out and I?m happy to say it ran great, engine just purred along beautifully. Now we?ll just have to wait and see how long it last. Fingers are crossed and knocked on wood. Thanks to all that helped me here, you all are great.