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JacobSlabach

Locked up Honda Foreman 400 full rebuild

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So this’ll be long I’ll give all the background first to see my issue skip to the ***

Hey I picked up a pit bike and a foreman for 800 the pit bike was running but the foreman was locked up.  Sold the pit bike but when I took the top end off the piston I only found half a piston left.  So knowing the rest of the piston was down in the crankcase I knew it had to be pulled and gone thru completely.

to pull the motor I went ahead and pulled the rear end off and unbolted the front diff to pull the drive shafts and pull the motor.  Now I have the motor torn down completely and have all the parts of the piston removed.  I know the rod and crankshaft is shot (heat discoloration and too much up and down play rod to crankshaft).  
 

***so I’m wondering while I have the motor apart what should I check for?  I know this motor died from heat as the oil in the head smelled like popcorn.  So what should I check to make sure I fix the issue (overheating I assume) and not just the symptoms (blown up motor lol).

so put simply I don’t want to just rebuild the motor to have it overheat and repeat the process after 5mins of running

Here’s some pics

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7AAC7DF8-4C2E-43DF-B55F-F581E14B866F.jpeg

18915631-4FC7-4128-A40E-4EFCB7880B29.jpeg

B660A37B-968A-4BF4-9B84-7B1CF70A88F5.jpeg

3040B256-0DED-4243-8006-5843D0070941.jpeg

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Well to tell you the truth, that doesn't particularly look like a motor that died from overheating. Mostly if they overheat they seize the piston in the bore, but not smash the piston to bits like that.

Does the bore have signs of it locking up, like aluminum stuck to the walls of  ?

And which bit was seized ? It wouldn't have been that piston/bore I'd bet.

I'd assume that it was just an old worn out motor that was making noises and eventually got a big rev and broke the side of it's piston because of the way it was rattling around in there.

And the top ends often smell like overheated oil..

I'd inspect everything for the usual signs of wear and damage and then go ahead and overhaul it. I've done heaps of motors that looked like that, and worse, and they all rebuilt just fine.

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That’s good news to hear.  So I think it was the wrist pin that seized.  Not sure if that could have broken the piston but I can’t hammer it out to get the piston off the rod and the rod has heat discoloration on it.  Maybe maybe not but either way I should replace the rod and crankshaft correct?  And I noticed the oil pump felt worn out and there was no oil in the oil cooler when I unhooked it from the motor.

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Yeah you have to replace the conrod.. You don't replace the whole crank, just a new pin the conrod runs on. So rod, roller bearings and pin get replaced. And unless you have a good workshop you need someone to press the crank apart and together and lined up.

Don't get conned into getting the crank balanced.. that's a bit of bullshit you might get hit with. If the people doing the pressing do a good job, that's all that's needed. And it doesn't take much to do a good job.. My sons were doing them for themselves when they were fourteen..

There's probably an oil restricter in the crankcase oilway that stops too much oil pressure/flow going to the head and cam. Make sure you find that and blow it backwards.. It gets blocked easily and people overlook them and the cams run dry.

The wrist pin should press out with a palm push so yeah it's seized.. You'll get the new one in with your hand.

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Any tips on how to press apart the crankshaft and put it back together properly?  And thanks so I hear you saying the crankshaft is good, the rod is bad right?  The crankshaft did have some heat discoloration on it as well not sure if that makes a difference.

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The crank is in three parts, left, right and the pin. You have to replace the pin, because the rollers run on it, and the conrod because the rollers run in it.

Getting it apart and together you might do with pullers and/or threaded rods, and a thick steel plate with a wide slot cut in it to go around the conrod, which is how I do them, but you need two centers or a lathe to spin the crank between, and a dti gauge to check it for runout and alignment. If you don't have the centres and dti gauge then it's better to get it done by a bike shop or precision engineer. And.. given the choices between engineer and bike shop, you're better off with the bike shop. The engineer will be scared of it and try to tell you it's a tricky business, the bike shop will be doing them all the time.. and will charge you a fair price.

Yeah ignore the heat marks... the new rod when you get it will have heat marks from it's manufacture already probably. And the crank throws are just soft steel.. no worries.

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If you are really keen, and feel confident to do it, and have the gear... I'll tell you how the crank job's done.

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And yeah... replace the oil pump if you are at all concerned about that !

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yea id rather do it myself if the tools needed dont cost an arm and a leg.  dont have much of a shop but id love to learn how to rebuild the crankshaft rather then pay someone else to do it.  what tools would be required?

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The cooler should have signs of oil, but it might have drained away by the time you got to it. You need to clean that cooler out, and when you put the motor back together you want to leave the return of the cooler off and in a bucket to check it's flowing and to flush it out with clean oil.

For one crank it's barely worth setting up the stuff you need, for ongoing work it's cheap though. You'll need a thick steel plate(14/16mm) with a wide slot gas-axed in it that will fit between the two crank webs and around the con rod nicely, a dti gauge and stand for it(not too dear and handy for lots of stuff), and some sort of set up that has two "centers". Centers are just round rods with 60 degree tapers on the ends that fit into the ends of the crank so you can spin the crank on them without any wobble. The centers don't have to be anything fancy at all, you could just grind them with a bench grinder if you are careful. To do the pulling/pressing you can use threaded rods or a hydraulic puller and a bit of box section or chunky angle iron, or a twenty ton press. To set up a "center" arrangement you could make the two centers and fit them into the gudgeon pin holes of two big conrods off some truck or old car, then use the cap holding bolts and two steel plates to clamp them to a long steel strap or angle iron, the idea being that you can slide them along the strap to get the crank in between the centers and then together so the crank spins by it's ends between the centers. They need to slide nicely so you can get them a bit tight in the ends of the crank so there's no wobble, and you need to be able to get the crank in and out easily because you are going to need to take it out of there after every measure to hit the crank with a hammer to do the adjusting, then back in for another measure.

You'll also need some drills to make holes in the thick steel plate for the 14/16mm threaded rods.

The thick plate with the conrod slot has to be wide/big enough to poke out the sides of the crank far enough that you can drill two holes that will be directly in line with the crank pin you want to press out, or so the two legged puller can grip it on opposite sides of the crank pin. I use a round plate about 160mm diam, but it could be square.. As long as it's strong still after the slot is in it. Once all these things are arranged you can do most cranks.

The actual work involved to overhaul the crank is quite minimum. As little as an hour and a half once you've done a few and got the idea about what you are doing and  how hard to tap them to align things.

Edited by Mech
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A little  NZ to  USA translation..

DTI gauge -  Dial indicator and stand

Gas Axed  -  cutting torched

Gudgeon pin  Wrist pin  or  piston  pin

16mm  -       5/8 "

160mm  -     6"

Edited by davefrombc
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"Onya" stands for "good on you", and it's common over here..

And If I call anyone "mate".. it means "pal", I believe.. not lover..  Just to clarify before there's any embarrassing misunderstandings !

 

Or is it "buddy" over there.

Edited by Mech

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On 12/31/2020 at 6:33 PM, Mech said:

"Onya" stands for "good on you", and it's common over here..

And If I call anyone "mate".. it means "pal", I believe.. not lover..  Just to clarify before there's any embarrassing misunderstandings !

 

Or is it "buddy" over there.

haha yea i understand i believe we have a few other members from out of the states here as well.  thanks for explaining everything and i will give her a shot once i get some free time.. been needing to buy a 20 ton press for a while now, just needed a good enough excuse to throw some $$$ that way and get one.  and thanks @davefrombc for the translation 😆.  also have a beat up scrambler 850 that im fixing up so with both projects going at the same time, i may be slow getting back to this one.  but i think it will be worth it to do it myself because i dont want to pay someone else to, i plan to do this sort of thing regularly in the future so im sure i will use these tools again, and knowledge i believe is valuable especially in this day and age.

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Yeah it's good to learn new skills, and asking is the way to go.

I used to tell my sons that everyone likes showing young people(not saying you are one), what they know... I told them that if they asked, people would go out of their way to impart their knowledge.. My sons used to play it to the max.. Way to learn though. And knowledge needs passing on or the old ways get lost..

I\m happy to share what I know.

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1 hour ago, Mech said:

Yeah it's good to learn new skills, and asking is the way to go.

I used to tell my sons that everyone likes showing young people(not saying you are one), what they know... I told them that if they asked, people would go out of their way to impart their knowledge.. My sons used to play it to the max.. Way to learn though. And knowledge needs passing on or the old ways get lost..

I\m happy to share what I know.

agree 100%.  and yes i am young lol, im 17

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but thanks to youtube and the folks here at quadcrazy and a couple other forums, ive made it thus far and am now helping my buddies whove got into atvs

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Yeah seventeen's young..  Lol..   I wish I was seventeen..

 

It's good to know enough not to be hostage to thieving mechanics..

 

All power to you.

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