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Discussion Starter · #1 ·
A month or so ago, I posted that my cm400 had developed a tapping sound and it seems the concensus was that I'd lost some of the rubber dampers on the balancer sprocket. Haven't torn into the motor to see if that is the case yet, not riding much due to the noise, but have noticed that when I do ride it, it overheats to the point that it won't turn over. Sounds like something is dragging if I try to kick it over, electric starter just won't turn it over at all. Let it cool for a bit and it starts right up. I'm riding it on country roads, at maybe 5000 rpm's, no traffic, so it shouldn't overheat. Outside temp is about 85 degrees farenheit. Trip is 6 miles to town and 6 back. It does ok the first half, but unless I let it cool off, it is hot when I get home and won't turn over. Plugs look good. Adjusted valves a short time ago with engine warm, but not super hot. Running regular unleaded gas with no alcohol in it.
What would make it do this?
 

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I suspect that this is a case where the left rod bearing has failed, it gets hot at the rod big end and starts to almost weld itself to the crank. I've seen this before where it gets hot and dramatic loss of power until it stops, let it cool down and it'll restart and run until hot again. Eventually the starter won't turn it over even dead cold.
 

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Discussion Starter · #4 ·
I suspect that this is a case where the left rod bearing has failed, it gets hot at the rod big end and starts to almost weld itself to the crank. I've seen this before where it gets hot and dramatic loss of power until it stops, let it cool down and it'll restart and run until hot again. Eventually the starter won't turn it over even dead cold.
Could this also be the source of my tap, tap, tapping? It gets louder as the engine warms up. I suspect you are correct, as I don't think it's too lean, actually had the pilot screws turned out an extra turn and had some soot on the plugs, and it seems to be getting oil to the camshaft. Also, when I force it over with the kick starter, it sound like something dry trying to turn. Guess I best not drive it until I tear it down. Hope the crank is still ok. It's got about 35,000 miles but seems to have good compression and doesn't burn oil.
 

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Discussion Starter · #6 ·
Ok, I've taken everything loose except the bolts holding the engine in. I've got a floor jack, but it seems a little iffy just trying to lower the engine by myself. Any suggestions on how to get this thing out safely. I've got a come along I could attach somewhere and lower it to the floor, or maybe put a stand small bench under it and attempt to lift the bike off of it. Just seems a bit unweildy and I don't want to hurt myself or the engine.
 

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Since there's wiggling and tipping to be done getting the engine out, not much but enough, a floor jack isn't a good choice since it'll slip off the jack and crash to the ground.
If there's a viable ceiling joist above the bike then I'd use the come along to lift the bike off the engine once the engine is fully supported on a crate, etc.
I've used a floor motorcycle lift with wood across the arms to remove/install easily.
GEDC2254.jpg
 

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Discussion Starter · #8 ·
Since there's wiggling and tipping to be done getting the engine out, not much but enough, a floor jack isn't a good choice since it'll slip off the jack and crash to the ground.
If there's a viable ceiling joist above the bike then I'd use the come along to lift the bike off the engine once the engine is fully supported on a crate, etc.
I've used a floor motorcycle lift with wood across the arms to remove/install easily.
View attachment 264932
Well I got it out using the come along. I just left the top support hooked to the jugs and hooked the come along in there to make sure it didn't fall to the ground, then used a small bench with two by to pry and wiggle till it was loose. Then I move that out of the way and lowered the engine via the come along. I had a steel bar overhead between two joists which I used years ago to move a tractor engine into place for attachment to the tractor. Been working on cleaning it up. Lots of years of oil and grime that I figure needs to be off there before I start taking it apart. Am a little puzzled by the gear shifter which protudes from the lower case that doesn't appear in the manual. I assume that just lifts out with the lower case as does the kick start shaft. And thanks for the advice. It will be a small miracle if I get this thing fixed and back together, as I'm not really a mechanic. I just figure it's no good to me as it is and would cost more than the bike is worth to pay a mechanic to tear into it and look for parts on ebay. Since I'm retired, why not.
 

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To split the case the rotor & stator on the left side come off, clutch ass'y and the shift rod get removed from the left side. Kicker stays in place.
There's a sticky in this section for making the clutch nut socket and you'll need a rotor puller bolt to get the rotor off, 20mm x 1.5 pitch. Motion Pro sells them
 

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The gear shifter shaft can stay in, you just need to disconnect the spring that attaches the mechanism to the other side of the case (it's an arm thing behind the clutch).

Take lots of pictures (or make sure the manual diagram is clear) even for stuff that seems obvious. Take your time and see how the engine works, I find it pretty fun to figure out what does what. I also find a sharpie and a bunch of thing cardboard is helpful for getting all the bolts back in the spots they came out of.

Also if you call local fastener stores someone might have the right size for less than 10$
 

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Discussion Starter · #11 ·
To split the case the rotor & stator on the left side come off, clutch ass'y and the shift rod get removed from the left side. Kicker stays in place.
There's a sticky in this section for making the clutch nut socket and you'll need a rotor puller bolt to get the rotor off, 20mm x 1.5 pitch. Motion Pro sells them
All very good info. I didn't realize this stuff had to come off before splitting the case, but I now see why the stator has to come off, still figuring out the clutch. However, I just read in the shop manual that I have to remove the head, cylinder and pistons to put in rod bearings and deal with the crankshaft. Can I not do all that from the bottom and leave the top end alone. The bike runs strong, no smoke and I hadn't planned to replace rings or rework the head, etc. I hope I'm not being a pain here, learning as I go.
 

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The top end does not need to come off to get to the rod bearings. edited to remove wrong info, getting the crankshaft out requires removing the top end, see below
 

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The top end does not need to come off to get to the rod bearings. If you need to get the rods out with the attached pistons that will be fine, just getting the pistons back in may be slightly harder due to lack of space to compress rings
The cam chain will prevent you from doing it this way, 80cm400t. The chain holds the crankshaft from getting out of the way, and the pistons won't pass by the crankshaft.
 

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It would be fine for the rod bearings and a few other things such as balancer chain, 80cm400t.
 

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Discussion Starter · #16 ·
Ok, it's me again. I've managed to split the case and see some of my problems. The rear balancer has eaten into it's shaft and is wobbly and hitting one of the gears, shearing off the corners of one of them. Probably has messed up the bearing cover, as I'm having difficulty getting the rear balancer out, even with the shaft removed. The shaft has a sizable groove cut into it. Lots of metal in the bottom of the case. I decided to just go ahear and pull the front balancer too, and can't get the shaft to slide out. Is it being held in by a bolt from the jugs which I didn't remove or something else? I don't see anything holding it, but I know the back one was held in by the bolt holding the oil screener and I'm wondering if the front shaft is similar. It's been a learning experience. Oh, I made a tool for the clutch per the sticky. It was a bitch, due to my poor skills at using the dremil tool, but it worked. Also a friend managed to find me an m20 x 1.5 bolt to remove the stator. Just need to get those balancers out, look for other damage and then parts.
 

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I think this is a case where pictures would really help.

I'm not sure what you mean by hitting the gears because they're pretty far away
IMG_7418.JPG
I don't remember the shaft being difficult to take out but I also had the top end off. Spring off, pin out, the adjuster nuts and plate off then slide it out (while rotating)
IMG_7419.JPG

Also from the state of the balancers I would be surprised if your rod bearings are intact, definitely check those next (quick way see if you can push and pull the rod caps away from/towards the crank)
 

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Discussion Starter · #18 ·
I think this is a case where pictures would really help.

I'm not sure what you mean by hitting the gears because they're pretty far away
View attachment 265086
I don't remember the shaft being difficult to take out but I also had the top end off. Spring off, pin out, the adjuster nuts and plate off then slide it out (while rotating)
View attachment 265092

Also from the state of the balancers I would be surprised if your rod bearings are intact, definitely check those next (quick way see if you can push and pull the rod caps away from/towards the crank)
It's the rear balancer that was hitting the gear and also digging into the side of the bearing cover it's mounted in. Pretty bad shape and will need replacing. I finally did get it out after posting. The front balancer seems fine, but I just can't get the shaft out even with the pin and spring removed. It turns and has a very small bit of play, but hits something when you try to slide it out. I haven't gotten to the bearings yet, though it seems they turn fine. No slop or binding. Certainly everything is full of metal from the rear balancer eating up the aluminum bearing cover, as well as metal from the shaft itself. The main journals look fine. I don't know why the rear balancer shaft went to hell. I don't have a way to do pics right now, but I'll try to get some and load them up. Thanks for the reply.
 

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Discussion Starter · #19 ·
On page 126 in the manual, there is a pick of the gears with adjacent rear balancer (You can just see the chain sprocket). The weight is maybe 1/4 inch from the gear when it rotates. Mine has sagged due to the shaft and weight wear and wobbles and is just nicking the corners of the largest gear.
 

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That picture in the manual makes more sense, I think my picture must have been with the bearing holder partially off. Either way, I don't know of a reason the shaft won't come out, maybe LDR or dtsmjr8dan will have an idea. Fingers crossed your rod bearings are okay and the balancers just decided to fail independently.
 
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