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Rebuilding 05' 450, What went wrong?

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So I am rebuilding my 05' 450. It bent the piston down and broke off the entire bottom of it, knicked the cylinder wall and messed up the head pretty good.

Im getting the head worked on and hopefully it will be useable. I am going to replace the exhaust valves because it lookes like they hit the piston, even though they are not bent, the piston looks like it must have impacted them. Im going to replace the cylinder and I have already split the case, which was full of chucks of piston. The crank, and everything else look good besides the cylinder, piston, head and the undamaged exhaust valves which im replacing anyway.

bdf01140.jpg

I plan on cleaning out all the bearings, replacing all the seals, and making sure the bike is put together well.

Im at the point where I'm trying to pinpoint what went wrong. the two things I found majorly wrong were:

1. Knick in the inside/gear side of the cam chain and a link that wont bend

2. The bike had no coolant. I always check this, but I had not this ride, and Im not sure where it went. It wasnt in the oil, and I dont think the radiator had any leaks, but who knows.

So I think it either over heated and this caused the piston to break.....OR....The cam chain knick caused the chain to jump throwing off the timing and smashing the exhaust valves into the piston. However the valves, like I said, dont really show any damage.

Would the heat have caused this kind of damage?

Any ideas what would cause the knick in my cam chain?

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New crank!? Aghh you guys are killing me!! Ohh well I really don't want to split this case any time soon......Might as well. It will be a minute before I can fix it anyway, hence getting the 03' working good enough to ride.

Any ideas what might have caused the burr in the cam chain? I'll get a photo of it tomorrow.

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It did make a slight knocking sound for about 30 seconds before the failure, for what it's worth.

The motor had 66.5 hours on it when the failure occured. I'm not sure if the motor was rebuilt at that point or if it was just for valve maintenance.

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no coolant left, and not in the oil, was likely a water pump seal pissing out the weap hole. Got real hot and worn piston .."boom".

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You already have the head and cylinder off, hell, you have all the hard stuff done! The cranks on those have to be the easiest that I have ever changed and you don't even need a case splitter! If the head is fubar'ed, look into bigborethumpers.com for a new head and everything. If you have to get new valves and if the head was all messed up from the debris, by the time you have it fixed (seats cut, new valves, etc...) you can buy this and be done with the head.

Edited by screnshaw400
more stuff

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The entire bike is apart the case is already split. I have the crank out and it looks fine, in all tolerances with the feeler gauge. But I understand why it's a good idea to put a new one in now.

So this is the burr in the cam chain. The is on the inside of the chain, on the gear tooth side. The link will not bend. Both cam chain gears look fine. I'm trying to figure out what damaged the chain like that.

acf57548.jpg

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The piston flipped sideways in the bore, no doubt about that, probably from getting too hot and too many hours on the piston. It looks like a stock piston. I don't see any sign of the piston skirt on the exhaust side of the piston, so it probably bent or snapped off close to the beginning of the stroke.

With the skirt missing, the piston flipped sideways on the exhaust stroke, smashed into the valves while the cam was trying to open them, extreme force dented the cam chain.

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The rest of the piston was in the bottom of the case before the one way oil valve.

Im hoping that none of it ended up in the bearings, and that I can clean them out and use them again. I dont think any metal got into them, but I'm going to clean them really good with carb cleaner and see what happens.

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Bearings are $50.00. change out the counterbalance bearings as well. Check the oil pump for galling and replace if necessary.

Do you really want to clean 50.00 in bearings? I think they spin about 10,800RPM or so.

If the bearing allows the crankshaft to radially move the connecting rod will move radially. Then the piston will TRY to move radially on the small pin.

Don't skimp on parts. It's just not worth it.

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The wrist pin hole has been compromised, you can bet on that. Rebuilding the crank isn't worth the money unless you send it to Crankworks in AZ and get one of their billet rods put on it.

That knick in the cam chain probably happened when the motor locked up. The inertia of the chain, the cam and all that slamming to a stock because the crank gear stopped dead.

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If you plan on keeping this bike i would put in mostly oem parts. Get them cheap from the tt store or service honda. I dont know what the word is on a new crank- oem or aftermarket. Shawn mc?? I do know plenty of people that have done rebuilds using the aftermarket bearings, seals etc... and have had no problems but I feel better using the oem stuff.

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more than likely the rod is bent, thus needs replaced. Replace all bearings and seals also. If you try to pinch pennies now, you will be back into the motor in a few rides.

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more than likely the rod is bent, thus needs replaced. Replace all bearings and seals also. If you try to pinch pennies now, you will be back into the motor in a few rides.

+1:thumbsup:

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more than likely the rod is bent, thus needs replaced. Replace all bearings and seals also. If you try to pinch pennies now, you will be back into the motor in a few rides.

Im the last guy in the world to pinch pennies on a quality build. But taking the bearings to a bearing house will get you the exact same bearings from the exact same manufacturer (usually, or better if you can get a Timken or something) for a lot less money. Seals too. They all have standardized pn's on them.

Just dickin around one day I found the 6305 main crank bearings (almost all full sized two strokes run it) instead of 55 bucks for the pair, it was listed at 16 bucks for a pair. The seals were only 4 bucks each too.

But its easier to just hit up the OEM, or even All Balls...same bearings as OEM. :bonk:

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