Considering transmission overhaul myself - terrible idea, or awesome idea?

Phil_B

Noob trying to learn the basics-82 XS400 HS
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My names Phil. I'm the proud owner of an 81 XS400 which I love. I just picked up an 85 FJ600. Bought it non-running. I cleaned out the carbs and got all 4 cylinders firing. I thought everything was perfect until i put it in first and got nice cyclical click coming from the transmission. haha.

I thought I would post here as the DOHC motor is very similar to those on many maxim models, and though many people here might have some insight into the issue and experience with similar motors. Ill be cross posting this the at XJRider forum. But am having trouble getting it posted at the moment.

After doing some research (links below) it sounds like I have a tooth missing on the transmission. I believe the chain came off the rear sprocket similar to the guy in the first post, as there is some damage around the front sprocket. In-fact, the force was enough to break off the section of shielding (part of the case) directly above the sprocket, and also to chip off part of the cap of the starter (black plastic cap at the end where the bolts go through to attach it).

https://thumpertalk.com/forums/topic/819111-ttr125-first-gear-clicking/
https://thumpertalk.com/forums/topic/960777-ttr125-broken-tooth-on-first-gear/

To describe the issue, once i put the bike into first gear I get a rhythmic click that corresponds to the amount of throttle, more throttle faster click. But, when i go into second the sound is gone. If i kill the motor and walk the bike forward in first gear I can also hear the click, but much more quietly. However, if i put the bike on the centre stand and give it throttle in first the sound is not really noticeable if at all....but, when the bike idles there also appears to be a kind rhythmic of knock coming from the transmission area.

So........this leads to the question i have for the people here who are more knowledgeable than my self. And, i should also say my mechanical ability is so far no more advance than: cleaning crabs, calipers, changing for oil, and a drum break. I have no engine experience.

1) Can I just replace the first gear cog or do i need a whole new transmission set? (assuming this is the only issue I find.
2) Am i crazy for even considering undertaking this repair by my-self? I'm in no rush as I have a bike to ride, and will have all of winter to do the work.
3) Can someone give me a basic idea what will be involved? I know the motor will have to come out and then ill have to drain it, flip it and crack open the bottom portion of crank case.
4) Will repairing the transmission gears require special calibration, tuning, and tools? Or will it essentially drop in where the old transmission gear set is?
5) Are there any obvious/specific pitfalls I might face? Or specialized tools I will need

Oh, I should mention that I have the Haynes service manual which will guide me. And also, that i understand that this will be an exercise in organization and planning, lots of bagging, labelling, pictures, and maybe video will be used to help me get it back together. I'm not a mechanic, but my job involves problem solving and patience, so maybe this is the right kind of challenge for me, even though I'm low on mechanical experience.

My ultimate plan is to convert my FJ600 it to a street fighter or cafe style mod. Basically one way or another the front cowling is coming off! As you can see at some point it received a rather horrendous paint job.

Okay, thanks for reading. Ill appreciate any advice, wisdom, or information. Looking forward to hearing your thoughts!
 

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Ill give this a go.

I would say that you sound like you are able to perform work at this level . Its really just following the instructions in the manuals and reading it over and over and really preparing yourself. The biggest part is just having the proper tools and a good CLEAN space with a comfortable work area and proper lighting.

Before you tear into the engine, the engine should be thoroughly degreased and cleaned with a bucket of soap and hot water and a good bristle brush and whatever else you might use. It helps to have compressed air to blow it off. BLOCK OFF the intake and exhaust ports.

I would perform a compression test first. If the cylinders have inadequate results, you need to decide if you really want to do possibly both transmission rebuilding and top end rebuilding... I had well over $1000 into my XS360 top end rebuild and searching the entire world for parts, just to hear it start.

Once you get the case split, everything comes apart, the trans gearsets will pull out as two units. Usually, you can find complete gearsets. Your gearset should have ball bearings on the ends so you should be able to simply drop in a new set. MAKE sure you get the right sets. I purchased a gearset for my bike and didnt realize it was a 5 speed instead of 6. A 6 speed will have 6 gear cogs, and a 5 will have 5. I guess I bought a set from a XS400 Maxim...?

Inspect everything and check the cases for cracks, make sure the landings for the trans bearings arent galled or damaged. The gearsets are usually replaced as a whole, I suppose you can find each individual gear if you wanted to.

You will have to clean everything and get rid of all debris. Theres better methods to doing this, but I simply use soap and hot water. I connect a hose to my water heater and clean all the parts and I have paper towels, compressed air, and lots of oil..

I soak all my parts in a product called EZZOX. Its a multipurpose oil used on firearms and it is truly incredible stuff. Let the oil soak for a while and then wipe it off.. When I had my cylinders bored out. I put EEZOX on the bores and I stored the jug for almost a year without lubing it and it was flawless when I got back to it. I use this oil on everything.


Honestly, I would leave the cowl on lol.. Get a nice paint job and it could look really cool.
 

Thanks for the info NewHavenMike! That is encourging and its helping me convince myself to do the the work.

Yes, the engine will need a good cleaning and degreasing for sure.

I have been putting off the compression test. Probably just trying to avoid more bad news, keep myself motvated. If the top end is in trouble too that might be end of the road. Eject. But, im hopefull!

Thanks for all the advice! Ill defnitly keep it in mind. Ill definitely make a post as i get started. Probably not untill summer starts to wind-down. I may have some questions so i hope you will stay tuned.

On that note, Im curious ive seen people working on motors using a wood box-brance that apears to just be 2x4's, to place the motor inside of. Can someone explain the idea behind that to me?
 
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