[Antics14086]

A few weeks ago I picked up a mini bike on craigslist to fix and resell. And the test drives on the mini bike got me really itching for a real bike to work on (I've never owned or ridden anything on 2 wheels with an engine). A few days ago I came across a 1972 Kawasaki Trail Boss (The seller listed it as a 1971) for $100 on Craigslist, so I had to look into it more.

So a long story short, and a little haggling, we settled on $70, and I am now the proud owner of a mostly complete rolling chassis, a bin of parts, the original key?, and a bill of sale.

First question, at $70, is it worth rebuilding? It didn't seem too bad to me. With the cost of parts considered, I should still be able to make a profit if I choose to sell when it's done, but a big part of me is itching to keep it. I can also easily make my money back by selling a few parts, and end up way ahead.
And my girlfriend took a liking to it immediately as well. She wouldn't sit on the mini bike, but had no problems climbing right on the G4.

I have looked up the frame, and engine serials, and both confirm the bike as being a 1972, so the engine/frame are correct for the year, and the bike.

The bike was last registered April 1978, and last inspected March 1979, making April 1979 the last time it was legally driven on the road.

The bike has 2207 original miles

And after a couple hours figuring out what goes where, I do in fact have a pretty complete engine and transmission.

Now going through the engine, which was disassembled to replace a burned/blown piston (And the PO never completed it- but I have NOS parts for the piston, ring, and head gasket), I've found a little rust on the crank and connecting rod. I assume there's a little rust on the gears inside. This is all just surface rust, nothing rotted, scaling, falling off, or anything like that, but I wanted to know if there's a DIY trick to removing rust from the crank and connecting rod, that is SAFE for aluminum? Something like the vinegar soak for steel, but safe enough for aluminum?

For the record, I tried posting pictures, but I don't have enough posts

 

[MZ250]

Assuming you can take the parts out, I would just brush the rust off with a nylon wire wheel. They're great, and come in several grits from 80 to 240. Much easier on the hands and arms than metal ones, and with the 240 grit, can even be used to prep surfaces for painting. If you want to go the chemical route, there is an electrolysis method for getting rust out of an old gas tank that I'm sure can be adapted for use on other steel parts. Google it, it involves baking soda and a 12v rectifier. Did it to my 40 year old gas tank and it worked like a charm. If the tranny was sealed, I doubt there is any rust on the gears themselves, but if the cylinder head was left off and the oil was drained, there may well be surface rust all over. I would definitely keep the wire wheels away from the connecting rod bearing surfaces, of course. An ultra sonic cleaner may serve you well, though I have not had much luck with mine. Good old fashioned elbow grease always seems to be the final recourse. Good luck, I hope this helps a little. Even if you don't make a profit, it's a hobby, and hobbies cost money! All told, I just put $3000 in parts and who knows how much in labor into a bike that I could never sell for even $2000, but I'd do it again in a second. And do it better too.

 

[Antics14086]

Thanks for the reply.

I was trying to avoid pulling the main case apart during the process, and since it's an aluminum case, and a steel crank, gears and connecting rod, vinegar won't work, since I've seen a few people say it'll destroy aluminum.

Vinegar did work great on the rear shocks and springs though. They look really amazing. Driver quality, since there was some pitting, but I'll be happy to bolt them back on to the frame, when I finish the tear down and get that all cleaned and painted. But for the cost of a gallon of vinegar, it's doing a great job. I even have a couple gears sitting in it, the counter gear, high gear, low gear, and sprocket, and all are coming out great.

The engine came to me with the 2 side covers and all internals and gears off, but the clutch, 2 main halves, and all those parts were all complete. Head and piston were off, and I can actually see the surface rust on the connecting rod, crank, and a little on the gears. And the cylinder walls are of course covered in a layer of rust, which is actually the worst of the engine rust too.

I'll probably just end up pulling the case apart just to do it right, and for piece of mind. At least I'll know when I ride it, that I did everything properly. I was just hoping to avoid it if possible, since this is the first bike I've owned and worked on.

I know all about hobbies costing money lol. Every one of my hobbies is expensive. The only thing missing from my list of expensive hobbies is boating.

Although being a couple days into the project, I'm having a great time doing it. And a lot easier, and cheaper than rebuilding cars and trucks.

 

[MZ250]

I must admit that I was unaware of the vinegar trick. I wonder if it works on chrome? I have plenty of parts from my old Honda to experiment with, so I'm going to try it. BTW, if you want to get your post count up, go to the new member forum and welcome a bunch of people.

Ah, boating...I keep seeing old boats for sale by the roadside (I live near Lake Erie) and I always think, "I could fix that up!" Then I think of all the crap I already have in the queue to be "fixed up," and reluctantly restrain myself....

 

[Antics14086]

It does work on chrome too. I have my rear shocks in the vinegar now. If the rust is bad, the pitting will still be there, but it'll make rusty junk look good again, at the very least it'll be driver quality, which is what mine are. I'll post a bit this evening so I can post a couple pictures to show the results I'm seeing.

I'm pretty close to lake Erie myself, but in NY, so I'm always seeing boats for sale, occasionally for free, and I have to resist as well. I have more projects going on than I can handle. So what do I do? Buy a vintage Kawasaki lol.

I'm off to the store for some shopping, lunch with the girlfriend, and the usual bs, have a good one. I'll get some pictures up tonight, rain or shine.

Oh and the frame is fully stripped down now, degreased, and waiting to have all the paint removed, then POR15'ed.

 

[Antics14086]

Alright, I took a few pictures of the shocks to show how they're coming along, as well as a picture of the kickstarter, and the exhaust flange (from muffler pipe to head) which was fully covered in rust, and some grime. When I hit 15 posts I'll get the pictures up tonight.

 

[Antics14086]

Alright lets get some pictures in here!

Here's the bike how I got it, just a rolling chassis, gas tank wasn't bolted down, and a recycle bin full of parts. And the odometer

 

[Antics14086]

First picture is after a little wire wheel on a drill work. I decided to try the vinegar, since the wire wheel wouldn't be easy with the spring.

Second picture is right after putting the shocks, and other items into the vinegar, you can see the level of rust they had on them.

Third picture is only 45 minutes after sitting in the vinegar, and using a little aluminum foil for rubbing/polishing.

These pictures were all taken yesterday. And one of the shocks was much worse than the other.

 

[Antics14086]

These pictures were all taken today. After the pictures yesterday, between then, and today, I used a wood handle wire brush, with very little elbow grease needed, just simple brushing, then would rinse in the vinegar. If more time was needed, I'd let it sit an hour and give it another shot.

And the last two are of the kick staarter and the exhaust flange, which I mentioned earlier that the exhaust flange was 100% covered in rust, and as of earlier, was down to only about 10% rust remaining.

 

[MZ250]

Wow, nice work, I'm definitely trying vinegar on the Honda. Keep the pics coming. I did my spoke wheels with just the wire wheels, took an hour a wheel, but I got every nook. The 240 grit nylon wheel really puts a nice shine on them, but mine weren't chrome.

 

[Antics14086]

The chrome may need some kind of clear coat when it's done, when I took the shocks out I noticed a little surface rust start as they dried, but it could have just been leftovers from the bin. I'm going to take them out and pressure wash them tomorrow and see what happens there, I'll keep you posted on the results.

I got all the frame parts stripped of paint today (except the kickstand), chemical stripper saved me a ton of time there. They'll be ready for POR tomorrow. And I have 2 coats of POR on the tank. Tomorrow I'll be doing the underside where it slides over the frame.

All my parts are being degreased, then paint stripped- which involves a little hand wire brush again and some pressure washer help as well. Dried, then cleaned with mineral spirits, dried, then POR surface prep for 30 minutes, pressure washed, dried, then the POR15 coat goes on.

It's a time consuming process, but should be worth it when the bike is done. The plan is to go all out and get the entire chassis done before winter, so I can put the bike in the shed, then a full engine and trans rebuild in my computer room over the winter.

I'm on the fence about the wheels right now. The spokes are 100% covered in rust- there will definitely be serious pitting, aluminum hubs are fine, and the wheels both have a bit of rust and will likely have some pitting as well. I'm currently considering painting the wheels until I can get my hands on a couple real nice ones down the road.

Do you have any pictures of your work? I'd love to see how it came out.

 

[MZ250]

Well, I haven't made any photo-worthy progress on the Honda yet, just got it stripped down, labeled and bagged. I just put one of the chrome front fork covers in vinegar, we'll see how it looks tomorrow. I did finally get a reprint of the Honda 90 manual in the mail, but I'm still less than certain of exactly what model it is! Some have a 90cc motor, others have a 65cc. 99% it's a 65, since the VIN starts with S65. The motor needs a total rebuild and a new crankcase half, I have found a crankcase and a head rebuild kit, but they claim it fits the S90 and the S65, which I really don't think is possible. I may have a few new spare parts for sale when all is said and done....

 

[Antics14086]

Any progress is photo worthy. Even partially, or fully stripped is cool to show off. Just stripping a bike is a lot of work.

Right now I have my frame pieces being tested for how well the paint adheres to the POR15. I shot a few of them yesterday with the final color. Some were scuffed first, some were not, I'll be heading out in a few minutes to check on that.

My bike knowledge is limited, so I can't really help with the ID other than googling it. Something to keep in mind, people do swap engines. Especially on older cars and bikes. And it's also somewhat common that the new engine is not the same as what was originally on there. Sometimes it's bigger, sometimes it's smaller.

For my bike, I was able to find a build chart with serial numbers, since mine was never issued a factory VIN, and my frame, and engine serial numbers are both within the range for the 1972 G4TRB, which is how I knew the seller listed it incorrectly. My bike was however BUILT in September of 1971 for the 1972 model year, this was listed on the label from the factory on the head tube.

 

[MZ250]

I finally found a thread that shed some light on decoding my vin, turns out it is an S65, and they were all the same through 1969. I pulled my cover out of the vinegar today, the rust pretty much wipes right off. My plan is to do all the chrome in matte black and the frame in a bright silver, thus saving me the trouble of finding new chrome, but after a few hours on ebay, finding new chrome might not be a bad option. Tore apart the engine today (somewhat) and it is totally shot. I already ordered a total top end replacement kit, crankcase halves and a clutch, so basically all I'm using from the old engine is the tranny. I'm going to post some pics of this in a new thread about the resto, this will definitely be more of a project than the MZ. Someone already had their hands in the motor, there are hammer marks on the ignition rotor! I hope I can find an electronic ignition upgrade...it may be easier just to buy a new engine, but easy isn't fun...right??

 

[Antics14086]

Kudos on finding out what you have.

The problem I'm running into with my chrome, is after the vinegar, it needs an immediate coating, or it'll just rust again. It's a killer trick to get rid of existing rust, but it won't stop new rust from forming.

I'm about halfway through the chassis now. frame done, gas tank done, wheels done, etc.. I need to do my fenders, lights, seat (which needs new foam and a new cover), and handlebars. And of course all the wiring and cables too, but I don't expect that to be too difficult.

The engine will come next.

Whoever was in your engine had no clue what they were doing. I've never worked on a real motorcycle in my life (I do have prior small engine, and car/truck engine experience though) and I'd never bang on the rotor with a hammer lol.

It sucks having to replace a ton of parts, but at least you'll know exactly what's on your bike, and you won't have any question as to the reliability of your engine when you're done. It'll be worth the time, and every single penny.

Same thing on my bike, every single nut, bolt, washer, and screw is being removed, cleaned, etc.. The entire frame was done like this, including head tube bearings. Everything comes out, gets cleaned, replaced, lubed, etc.. whatever is needed, I'm doing it.

Because when I get the guts to take this bike up to its top speed (which is about 60mph, which is great for me being a new rider), I don't want any worries about something failing me.

Easy is never fun, and it lacks that rewarding sense of accomplishment you get when you climb that final hurdle.

You can update your resto right in this thread man, keep it all in one place: http://www.motorcycleforum.com/showthread.php?t=172194

 

[Unkle Krusty]

Back to basics.

Lets start with the main parts. Do the two halves of the engine casings line up.
Does the rod turn freely on the crank. Are all the gears there. Are the two crank bearings okay. They are easy enough to replace. Rust will eat into case hardening, which is the crank bearings. If there is any jerky motion in the main bearing it will need to be replaced. Now you need a ten ton press and someone who knows how to take a crank apart, and put it back together. Provided you can get a new bearing. You will need to true the crank with a dial gauge, and assemble the crank and gearbox in the crank cases. the crank needs to be trued again and adjusted of it is not true. That is actually a neat part because you get to whack it with a heavy hammer. The cylinder can be lightly honed. You can make a base and head gasket.

If you get past the above, the rest is easy.

Unkle Crusty*

 

[Antics14086]

Much appreciated response.

Both main casing halves line up, and have not been disassembled yet to my knowledge (but will be soon when I rebuild it).

I have done a mock up assembly while figuring out where things go, and I do have all the other covers, and as far as I can tell they also fit nicely, very snug as well, as they take a little side to side work to get them on and off.

The entire engine turns freely by hand. Crank, rod, turn totally free. I do feel a little something when turning it, which I'm guessing is probably the jerky motion you described. I have to replace the rod to piston bearing anyways, might as well do them both. I have filled the case with some old motor oil (Oil is decent still, as I change the oil on my vehicles regularly) to keep things covered and lubricated for now.

Base gasket was just paper, I can easily cut my own, or use RTV. I have a NOS head gasket, piston, and rings. (Original boxes for the rings and piston, which was nice to see)

Cylinder is iffy. I might just pick up a new head on Ebay, as they're cheap enough ($30 +/-). Entire cylinder is covered in rust to the point that rubbing it will knock some rust loose. The old piston, which was included, also shows serious scoring on two sides, as well as a broken bottom piece. I don't know if some kind of mechanical problem caused the scoring on the piston, but I don't want to skimp on $30, and end up screwing up the engine.

The truing of the crank will be new to me, everything else seems easy enough, or I've already done it in similar applications.

Thanks again, you just boosted my confidence level on the project.