Rebuilding motor, what's needed?

djsquare214 · Jan 10, 2017

Hey guys, about to put my motor back together.
Had the notorious piston rod bend on me and take out one of the pistons and cylinders.
Have the new crank, piston and cylinder ready to be put back together.
Other than a new gasket set and fluids, what will I be needing?

-Repack the bearing grease? New PTO bearing(s)?
-Oils/fluids/lubrication?
-New reeds?
-Etc?

Thanks guys!

sled_guy · Jan 10, 2017

Polaris doesn't use grease in the big block cranks, which I'm assuming you are working on. The new crank should have all new or at least inspected bearings already.

Inspect the reeds, but unless something flew through them they should be ok unless they have lots of miles on them. Just look for chipped ends.

New pistons/rings and rod end bearings while you are in there. Have you prepped the old, good cylinder with a light hone?

How does your case look? Where the bearings are pinched in the case. The big blocks were infamous for pounding a groove in the case which requires a line bore.

You'll want a new water pump belt too. Clean the valves good.

Rebuild and balance your clutch. Make sure it is 100% solid and tight and then have it balanced.

Check your motor mounts, especially the front left one.

sled_guy

djsquare214 · Jan 10, 2017

sled_guy said:
Polaris doesn't use grease in the big block cranks, which I'm assuming you are working on. The new crank should have all new or at least inspected bearings already.

-----It's a used crank, but worked well before it was removed.

Inspect the reeds, but unless something flew through them they should be ok unless they have lots of miles on them. Just look for chipped ends.

----Thanks for the tip, I'll have a look at them and replace if needed.

New pistons/rings and rod end bearings while you are in there. Have you prepped the old, good cylinder with a light hone?

-----Ok, I'll grab new pistons, rings and end bearings. Thanks, I almost bought 1 used piston, but new rings are a no brainer. Haven't honed yet, but I plan on doing so.

How does your case look? Where the bearings are pinched in the case. The big blocks were infamous for pounding a groove in the case which requires a line bore.

-----No groove that I can see, case looks minty (thank god)

You'll want a new water pump belt too. Clean the valves good.

-----Good tip, I'll grab the belt and clean those valves good!

Rebuild and balance your clutch. Make sure it is 100% solid and tight and then have it balanced.

------Another good tip! Will have it balance when I take it in.

Check your motor mounts, especially the front left one.

------ Once again, awesome tip, thanks

sled_guy

Thanks so much for the help. Just need to get this thing running to I can sell it to make room for another

Goinboardin · Jan 10, 2017

Good info above. I can't stress the case issue enough. It may look fine, good chance it should be line honed for proper bearing crush. Depends if you're just trying to get it to run a few hundred miles or last. If I were interested in making it last, I'd be sending my case to indy specialties in Minnesota to be line honed, with the crank to be trued, and clutch to be balanced, fresh movable sheave and cover bushing, sheave faces cleaned up, and have him set the belt to sheave clearance nice and tight for whatever belts you run. Sloppy belt to sheave clearance is like a slide hammer on the PTO end of the crank every time the clutch engages. I tried to run/build these motors on the cheap and it was a mistake.

Edit: I was typing as you posted that you're just trying to sell it. Since they're not really worth much, hard to justify doing it right. Possible bummer for the buyer but anyone with Google should know what they're getting into with these motors. It might last though, some do.

djsquare214 · Jan 10, 2017

Edit: I was typing as you posted that you're just trying to sell it. Since they're not really worth much, hard to justify doing it right. Possible bummer for the buyer but anyone with Google should know what they're getting into with these motors. It might last though, some do.[/QUOTE]

That's exactly it. I would love to get the case inspected/honed as well as balancing the crank, etc.... But since I'm just trying to sell it, I can't justify spending all that extra money when it's going to be hard to sell it, let alone trying to get my money back in labour and parts.

I was going to part it out, but didn't wan't to be sitting on parts and a chassis with my limited storage room.
So I figure if I can get it running for cheap, if I sell it for the right price, the owner will hopefully do some research and get the honing done or just run it into the ground.

PS- Can I get away with one new piston as the other looks mint? I'll get new rings for both for sure, but just wondering about the piston.

Rick E · Jan 11, 2017

djsquare214 said:
........... Just need to get this thing running so I can sell it
I would love to get the case inspected/honed as well as balancing the crank, etc.... But since I'm just trying to sell it, I can't justify spending all that extra money when it's going to be hard to sell it, let alone trying to get my money back in labour and parts.

Remember...... what goes around comes around. It's called "Karma"!

.

sled_guy · Jan 11, 2017

You can do one piston if the other one is fine. But you need to match the same brand of piston. So if the good one is the stock Polaris one then a single Polaris piston will cost you more than 2 after market ones.

sled_guy

peaceofwork · Jan 11, 2017

ummm just good enough to sell ?
I liked that karma statement above

Rick E · Jan 12, 2017

peaceofwork said:
ummm just good enough to sell ?
I liked that karma statement above

It may be soon, or it may be years from now..... but it will come back!

Drewd · Jan 12, 2017

peaceofwork said:
ummm just good enough to sell ?
I liked that karma statement above

As long as he discloses what was done to the engine, it is buyer's responsibility to determine the adequacy of the "rebuild."

There are tons of sleds on craigslist and classified websites that have rebuilds that involved the bare minimum.

Did I do a bore line/bearing crush check on my crank when I replaced it? NOPE. I did put some loctite stuff on the outer race on my crank bearings to ensure they don't spin. Good enough to get another year or two out of the wife's sled.

peaceofwork · Jan 12, 2017

i would like to see how the add for this machine would read

mtncat1 · Jan 12, 2017

it is not normal operating procedure to line bore a 2 stroke crank case s or balance clutches for that matter . a good quality crank , a set of cases in shape cylinders to spec and new pistons and gaskets, as far as selling it be honest with the buyer , but what is above is what any normal shop would do to repair that engine . sorry if i offended anyone .

Goinboardin · Jan 12, 2017

mtncat1 said:
it is not normal operating procedure to line bore a 2 stroke crank case s or balance clutches for that matter . a good quality crank , a set of cases in shape cylinders to spec and new pistons and gaskets, as far as selling it be honest with the buyer , but what is above is what any normal shop would do to repair that engine . sorry if i offended anyone .

That's certainly true.

Ideally, because its a Polaris bb800 with known case issues, it'd be line honed but that is not normal. I skipped that step each time I built my old 04' engine. Once it lasted ~1600 miles or so, another a few hundred (junk crank, I shouldn't have used it but I wanted to ride immediately), and with a perfect (new, balanced, shimmed properly) clutch and good crank I got 500 miles. I had twin pipes, 13.5:1 domes, and a 174" so it was getting the screws put to it. A mostly stock sled would likely last a while longer.

Just be honest about what was done & you're good in my book. These old sleds aren't worth much, need to keep that in perspective.

peaceofwork · Jan 13, 2017

good luck I hope you end up with the magic combo because I know it sure is a sad day when they self destruct, in my book a line bore is worth every penny

djsquare214 · Jan 13, 2017

Put yourself in my shoes.

You were given a sled with a bent rod due to a ruptured seal that let coolant into the cylinder while trying to start it. It hydro-locked and bent a rod.

The opposite cylinder/piston/rod/case all look mint, 100%.

You have 3 options:

1) You don't have much room to store the sled long term, so parting it out doesn't seem like a good way to go.

2) You could find good inspected used parts, and fix it yourself for $700, get it running and sell it cheap to hopefully make a tiny bit of profit. The owner can then decide to machine it or run it until it bends a crank again.

3) You could buy new parts, get the case inspected and machined all in for $2500 and sell it for HOPEFULLY $2500 so that the new owner can prolong his sled crank for a bit longer.

Call me crazy, but I'm all in for option #2.

Anyways, back on topic...

Can I clean the crank bearings with a degreaser and re-apply a sewing machine oil or a thin bearing oil?

I'm familiar with cleaning other sorts of bearings, but don't know much about crank bearings.

djsquare214 · Jan 13, 2017

Goinboardin said:
That's certainly true.

Ideally, because its a Polaris bb800 with known case issues, it'd be line honed but that is not normal. I skipped that step each time I built my old 04' engine. Once it lasted ~1600 miles or so, another a few hundred (junk crank, I shouldn't have used it but I wanted to ride immediately), and with a perfect (new, balanced, shimmed properly) clutch and good crank I got 500 miles. I had twin pipes, 13.5:1 domes, and a 174" so it was getting the screws put to it. A mostly stock sled would likely last a while longer.

Just be honest about what was done & you're good in my book. These old sleds aren't worth much, need to keep that in perspective.

Thanks for your answer! Very interesting.
If the sled was worth more or I was planning to keep it, I would fix it properly and spend more than it's worth.
I will not spend more than it's worth just to sell it to someone for no profit

Rick E · Jan 14, 2017

djsquare214 said:
Thanks for your answer! Very interesting.
If the sled was worth more or I was planning to keep it, I would fix it properly and spend more than it's worth.
Yes, and notice that this would be for YOU and YOUR use! I may do the same.

I will not spend more than it's worth just to sell it to someone for no profit
I fully understand that...... I would not want to do that either.

Perhaps put yourself in the position of a potential buyer!

It's your call....... just saying!

Another option would be to advertise it "as is" and at a reasonable price, and explain what it needs.
Do not spend any money on it...... and you'll likely break even anyway. (I.E., your "no profit" comment!)

.

djsquare214 · Jan 19, 2017

Oops, duplicated my reply and don't know how to delete this one lol

djsquare214 · Jan 19, 2017

Rick E said:
Perhaps put yourself in the position of a potential buyer!

It's your call....... just saying!

Another option would be to advertise it "as is" and at a reasonable price, and explain what it needs.
Do not spend any money on it...... and you'll likely break even anyway. (I.E., your "no profit" comment!)

.

If I was in the shoes of a potential buyer, I'd want everything on that sled to be new and to spec. Id want the owner to spend more than he should have, but that's obviously too good to be true for any used sale.

In the real world, I'll fix it for what I can, state what I've done to it in the ad, the potential buyer will get it for a great price, have lots of fun with it, and WHEN it blows again, he/she can make more than it's worth by parting it out.

Seems like a decent buy to me.

I like your idea of selling it "as is" without fixing it, but this goes back to my issue with storing it as I don't have much space. I might be sitting on it for another year verse having it running, might sell more quickly given the season. I would have gave that a second thought if I didn't already have all the parts ready to be put back together.

Thanks for the comments and all the previous comments, lots of good information, especially the comments on how most shops would fix it, and using the loctite on the outer bearing... Might give that a try... Good to know! Thanks!

whoisthatguy · Jan 31, 2017

An oil drain hole was left out of the crankcases, that would direct condensed oil to the critical PTO bearings. If you look down on the upper crankcase, you will see 3 oil drain holes when there should have been 4. The blockout for the mag side piston has 2 drain holes that direct oil to bearing on each side of the rod for that piston. On the PTO side, you only see one hole. The outer hole is missing because it needs to be drilled at a somewhat radical angle that is not possible with assembly line construction. So next time you have your crankcase halves apart, you might want to drill that hole in from the top, at the same position as the other holes, and direct it outward towards a location that will get oil to the PTO bearing. And the engine will last longer before the PTO bearing blows.

Rebuilding motor, what's needed?

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