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1970 SL100

Sad news, bmc. I've watched this thread with interest. My first real motorcycle was a SL100, as was my first wife's. Actually, hers had the "S" restriction for younger riders, at least on the tag. The actual engine was a SL125 with Powroll crank, some odd oversize Honda piston, Yoshimura cam and magnesium cylinder and ported head, Bassani pipe, CB450 carb, Barnett clutch, and Yoshimura close ratio 6-speed trans. It would run on top end faster than my stock XL250. We raced 100s and 125s in everything from short track to enduros to motocross. We even took a couple to Bonneville. Great little bikes. I hope some cases show up. If not, you can have the case TIG welded and rethreaded.
 
Indeed. I used to joke about Honda making screws out of lead. I removed quite a few with an impact driver, and had to slot a few more with a Dremel tool.

Is there room to use a Heli-Coil or a Timesert in the drain hole?

No, a big piece of the case came out with the bolt.
 
I decided to say screw it and bought a set of cases off of ebay. I hope they are usable.
 
I decided to just rebuild the entire engine. I ordered a set of cases off of e-bay and will just transfer all the parts off the old engine on to the new cases.

I took the old engine out of the frame and took it to the bench to disassemble it. Before I even got the engine out of the bike, I found more problems.

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One of the exhaust studs is broken it off, the pipe hid the problem. This motor has been through ****.

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All the screws and bolts look like this.

Now I've got a new head and cylinder on the way and the new cases have arrived, but they also show signs of poor maintenance.

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This is the oil drain bolt. I'm surprised the threads weren't stripped out of the case.

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You can see how squished the crush washer was here.

I'll spend the next week disassembling the old engine and getting the new cases and head ready. I'm going to take the head and cylinder to a machine shop to make sure everything is okay and figure out what size piston and rings I need. I've also got to figure what size rotor puller I need.
 
From what I can tell so far, all fixable. You seem to be a very good wrench and dedicated to doing a job the right way. Don't give up, we're all counting on you to revive our past.:clap:

Don't take this the wrong way. I always tell people who ask me if I can fix it, "How much do you want to spend. All it takes is money and time and I've got the time if you've got the money." That is easier said than done. It does take a bit of american enginuity, know how and determination to see a project like this through. I have faith.
 
Oh, BTW that green crud is from reformulated gas. Aslo known as oxiginated gas. So those of you who do not run your gas powered equipment more than once every three or four months, there ya go. That is those who live in the big 5 Texas cities anyway. Up here in Okieville, we still get 100% gas, no ethonal and no "oxiginated" stuff.
 
Made some progress today. The new ebay cases had been seperated since the crank and tranny was missing, but **** if three of the screws weren't frozen.

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This is what they looked like, I couldn't get them out even with an impact driver.

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After several heat cycles with a propane torch and three nights soaking with liquid wrench one finally came loose. I was afraid I'd break the easyout if I put any more pressure on it so I decided to drill a little larger hole and use a bigger easy out on the other two.

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I got one more out like that.

Then I realized that the threads only went into the other case and if I drilled out the head of the screw I could just pull the cases apart.

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I wish I'd done this in the beginning!

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The new cases.

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This is the cam chain tensioner, it has to be removed to bead blast the cases.

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This mechanism pushes down on the tensioner which bows to tension the chain.

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I cleaned up the gasket surface with a dull scraper. I'll take them to the machine shop when I take the head and cylinder. I'll have them pull the two bearings and then bead blast the cases in preparation for painting. You can see the original machining on the bottom gasket surface of the case.

Then I went to work on the engine. The oil filter, the oil pump and the clutch have to be removed from the right side.


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The oil filter.

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Once you remove three copper screws there is a special bolt holding it on the shaft.

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The socket you need for most of the early Honda bikes.

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The nut removed from the oil filter. This is a centrifical filter which spins the oil to seperate it from sludge. Not much of a filter, no wonder the oil change interval is 1000 miles.

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The filter sits on a splined shaft. I used the penney to keep the crankshaft from turning while I removed the bolt.

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This is the oil screen which sits on the opposite of the oil filter. All the oil passes through this screen before entering the filter. I think I need a new one.

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Two bolts hold on the oil pump cover. I like these ratcheting wrenches.

I'll finish taking off the oil pump and remove the clutch tomorrow.
 
My 1970 CL-100 had an oil pump failure with the expected loss of pressure and subsequent seizure. The centrifugal "filter" contained some gray aluminum sludge, but nothing else. After cleaning and reassembly, it ran fine. Japanese engines were like the proverbial axe - occasionally replace the head or the handle and they'll go on forever. Judging from the quality of the hardware, it was never intended to be taken apart. Screws were pretty much a one-time-use item.
 
My 1970 CL-100 had an oil pump failure with the expected loss of pressure and subsequent seizure. The centrifugal "filter" contained some gray aluminum sludge, but nothing else. After cleaning and reassembly, it ran fine. Japanese engines were like the proverbial axe - occasionally replace the head or the handle and they'll go on forever. Judging from the quality of the hardware, it was never intended to be taken apart. Screws were pretty much a one-time-use item.

I think they were considered disposable at the time because it'd cost way more to fix them than replace them. I busted a case on my 1970 in '71 or '72 and it cost me (mom) over $300 to get it fixed on a $465 bike.
 
Yep, my XL250 had a similar pump and likwise a failure. It looks like it turned out to be a good thing you had issues and had to tear it down. If not you would most certainly had problems and been doing it anyway.

Hey, I'm impressed, I knew you could do it:clap:
 
I removed all the parts I can off the bottom end and took off the top end today. I'm stuck until I get the rotor puller I ordered from Motion Pro. I halfheartedly looked for a 16 mm 1.5 bolt today, but no one seems to stock one that large.

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The clutch was pretty easy to get off, pull out the actuator, loosen four bolts and slip off this collar that holds the springs.

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Then this circlip comes off and off comes the clutch basket along with the steel and fiber plates. This was a wierd looking circlip--there weren't any holes in the end to grab.

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This is next item to come off, its called the external shift mechanism. The engine shift actually exits the case on the right side and uses this mechanism to connect to the shift shaft which then transverses the entire engine and comes out on the left. I guess the bottom end of this engine dates from the time when things shifted on the right.

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The removal steps.

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this is one of the things you have to be aware of when you take things apart. That little nub looks like its molded into that bushing sticking out of the case.

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In reality, its a small piece of metal which is easily lost if you don't know it comes out.

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Everything is off the right side of the engine.

Off with its head.

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Removing the points and mechanical advancer to pull the cam. More of the same type of screw heads. I had to get out the easy out again.

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removing the head only required removing four acorn nuts and one long bolt plus disconnecting the cam tensioner. This is the bolt that secured the cam tensioner. More hamfisted mechanics. I don't know why this bolt didn't strip out the threads from the head or break off in the head.

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The head removed.

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I turned the crank and the piston movement popped the cylinder off the cases. Cool, I've had to fight some of these for hours to get the head off. Multicylinder bikes can take days.

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piston and rings don't look good.

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Neither does the cam tensioner. The guide which goes on the other side looked pretty good though.

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This is the journal in the head where the cam rides. Its gouged and scored. Luckily, I bought another head when I bought the cylinder. They came off the same bike and I thought it'd be a good idea to keep them as a set.

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I wiggled the piston to see if it had any play in the wrist pin and it did. Problem is I don't know if its the pin, the conneting rod or the piston. I probably should replace all three if I can find the parts. It all depends what the machine shop tells me about the cylinder bore.

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the piston and rod look bad.

I have to get my head around the parts I'll need and I'm terriable at making lists.

The rotor puller should be in Wednesday and I can split the cases and take out the crank. This is a two piece crank and I'll need the machine shop to take it apart and replace the connecting rod if I go that route.

Stay tuned.
 
It just amazes we how we ever got stuff like this done back in the day. Modern tools are such a time and part saver today. I remember whenever I got a new bike buying an Allen head screw kit to replace the all the Phillips headed screws on the engine. Those kits where a popular sale item over the parts counter back then.

Now today, we have all kinds of easy outs, special drill bits, cobalt drill bits, Drill Doctors to perfectly sharpen those drill bits, cordless drills and impact drivers, etc. I’d be lost at work without them.
 
I'm taking the cylinder and case to the machine shop on Monday. I need them to measure the bore and tell me if I can just hone it and use the standard piston I have or if I'll need a rebore with new piston and rings. I'll also get them to remove the bearing fom the left side of the crankcase.

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Today I did an inventory of the gasket kit I bought and found its pretty complete, but there are lots of o-rings which weren't supplied. I'll have to order about 8 different ones for things like the clutch lever.

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I usually send stuff out to be sand blasted, but I've never been able to refinish aluminum parts to look like new so I decided to get a blast cabinet. This one from Harbor Freight was only $119 and I also picked up some glass bead which says its for aluminum.

Once I got the cabinet set up I cleaned up three of the case parts to be blasted. This thing uses a lot of air, but it works really nicely.

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Before

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After

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can you tell which one has been bead blasted?

I even tried it on the petcock.

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Before

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Halfway

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Finished. A new gasket kit and this will look and work like new.

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These two looked alike when I started.

Now I'm looking for anything aluminum to blast!
 
Soda is suppose to be a good medium to use on soft metals. Carb bodies and such.

That's what the guys on the SOHC forum use, but that seems expensive since you need about 5-10 lbs at a time. I also bought some crushed walnut shells which is the same consistency.
 
I bought a sand blast cabinet several years ago. Its great for the exact stuff your doing. However, the media itself tends to break down into a finer dust. Make sure you thuroughly clean all the parts afterwards.
 
Brings back lots of memories of my SL race dirt bikes of the early seventies.
Replaced lots of pieces on hopped up SL100-SL175's chasing two strokes.
 
I bought a sand blast cabinet several years ago. Its great for the exact stuff your doing. However, the media itself tends to break down into a finer dust. Make sure you thuroughly clean all the parts afterwards.

I noticed that, I'll be sure to clean everything thoroughly. I removed the bearings from the cases so I wouldn't have to worry about cleaning them up.
 
I dropped the cylinder, head and left case at the machine shop on Monday. He said the bore looked iffy so we'll see if I need a quick hone or a honest to goodness overbore. The valves are good, but I'm having the clearances checked, valve seal (only one) replace and valves lapped. There is only one valve seal, on the exhaust valve. Weird design.

There was a guy in there with a crank from a Ford 460 and he recognized the head right away as he was a certified Honda mechanic in another life. He said there was only one valve seal because the inlet valve was cooled by fuel and didn't need a seal. I guess when you are building these little bikes you have to cut costs every where you can to make a profit. How much does a valve seal cost? Multiply it by about a million world-wide and you're talking about real money.
 
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