New to the site just got an xs400 maxim!

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Keithp

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Hi all! My name is Keith. I just picked up a 1982 xs400 maxim. Has 2 brand new Harley tires, new electrical (stator,rectifier,plugs,wires,coils,etc) new clutch,cable,sprockets, chain, rebuilt carbs the list goes on and on! But it still wouldn't run. Found out why today. Has a hole in the right piston. I think the PO set the timing very wrong. But not sure. I'm debating on tearing down and doing a rebuild or just buying another motor for it. I found one local for $150 but have no guarantee on it running other than the guys word. I was wondering if anyone who has done this kind of job before could give me an idea of how much it will cost me myself to do. Or if I should say screw it and just get the motor.
 

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Welcome Keith! Yet another Maxim owner joins!

If you get the other motor, you could install it as is. Swapping motors should take a day or less, if you don't run into any problems.

Or you could take the time (a weekend?) to clean the new motor and transfer over all the new parts from the existing motor. I'd also suggest cleaning the carbs real well. They gum up real easy and my guess is this probably caused the holed piston. There isn't enough adjustment in the ignition timing to get the engine to run and cause pre-ignition. A lean mixture is much more likely to have caused the damage.

Finding good pistons and what ever else is needed, and rebuilding the engine will take much longer than a weekend, and cost more than $150.

Dave
 
Yeah I talked to the local guy with the spare. He says he can only guarantee it turns over. So that doesn't get me very far. Looks like I'm rebuilding.
 
Timing is non-adjustable on these engines, so that wasn't it. Your bike looks heavily modified. I wonder what all was done to it? You may find some interesting history when you tear into this bike...
 
Well so far I have torn down the motor and got the bad piston out. Also got some small pieces out of the case. Had to take the right side cover off and clean out the clutch. I think he had the bolts too tight. Wouldnt disengage. So got that working fine. Question though. I can't seem to find the torque specs on the right side cover. And ideas?
 
Pic of the tear down. Having fun. I've done a ton of car rebuilds but this is my first bike.
 

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Thats a nasty hole in the piston!

I think this happened because a previous owner was running the bike on one cylinder without any real combustion happening in one of the cylinders for a long time maybe??

This would unbalance the crankshaft causing it to get uneven. Over time this unevenness got so bad that the piston started hitting the spark plug and hit it repetitively for long enough to break a hole.

Your probably going to have to get the crankshaft balanced properly at a machine shop or buy a new crank shaft off ebay. I hope the rest of the bottom end engine isn't too rattled.
 
Is there any way I can verify that? If it gets to that point I will just look for a new motor! I'm not looking to get that deep into a rebuild. Any way to measure the connecting rods? The plugs that were in there looked fine no marks. And they definitely aren't new.
 
How are the rod bearings Im pretty sure you can find another piston for.I happen to have an extra 4.3 piston laying around in great shape do you think it will work?
 
Rod bearings seem great. No movement and no noise. I already ordered a set of pistons off eBay. Should be here tomorrow. Hoping I can get it together this weekend and see how it runs.
 
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That hole was caused by a lean mixture causing the cylinder to overheat, which lead to pre-ignition. Check the carb and intake boot. There is either dirt or corrosion in the carb or a vacuum leak.
 
bentwrench said:
Look under Appendices - Specifications - General Torque Specifications.

For bolts:
6mm 4.3 lb/ft
8mm 11 lb/ft
10m 22 lb/ft
12mm 40 lb/ft
14mm 61 lb/ft
16mm 94 lb/ft
Click to expand...

I seen this in there. What size are those bolts? I have an Allen key I'm using.
 
Rebuild is going great. Got the new pistons in and the heads back on. Gonna work on timing tomorrow and get some compression readings. Fixed a bunch of electrical connections that the PO half assed. Cleaned off the clutch plate and adjusted it nicely. Then I have to wait for uncle Sam to pay me so I can go shopping! Looking to get the following.

Pod filters
Plate frame with brake light and signals. I like this one.
Jet kit
Bar end mirrors

Very excited to possibly hear it running soon!

Question. On the back of the carbs there is a lever that slides to the side has little pump looking things on the ends. Is this my choke? It isn't hooked up to anything. I'm guessing the lever broke and PO disconnected it.
 
The "choke" is operated via a long transverse rod that opens and closes a "plunger" on each carb. The rod is held on by a few headless screws (not sure what their proper name is). The rod has a few indents to hold it in place (partial and full "choke") via two hidden ball bearings and springs. Without at least one of the ball bearings/springs the "choke" rod will not stay in place properly.

Mikesxs will have the jets you need individually; there is no need to buy an overpriced "jet kit."

Mikesxs also has some awesome "store brand" pod filters; whatever you get make sure there is no inner lip to block the opening to the carbs. Many cheap pod filters have an inner lip.

Those cheap led tails always worry me; I don't think they are very bright. There is no real way to know until you buy it because it is not DOT approved.
 

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