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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Discussion Starter · #1 ·
Yesterday, I finally got the stubborn heads off the freebie parts engine that I acquired last spring. My rubber mallet wasn't up to the job, but a 2x4 and a BFH got it done.



When the left head came off, I thought maybe this was why the crank won't turn:







Ouch!



Then I got the right head off:







That powder is a mix of rust and oxidized aluminum. I think this is the side that didn't have a spark plug when I got it.



I blew it out, tipped the block so the cylinder is vertical, and bathed the piston in penetrating oil.







This piston is so completely corroded in place, the fluid is still there after 24+ hours.



Then I picked out the pieces of the shattered piston (and the slightly twisted connecting rod) to find the real problem.







Just above the empty journal, you can see the clamp from the left conn rod, wedged between the crank and the engine case. Below the journal, and to the left (forward), you can just see a fragment of the piston skirt lodged in the transmission. If I could disconnect the right conn rod, I might be able to turn the crank backward enough to free the clamp, but I can only reach one bolt with the transmission installed. I can't extract the transmission without removing the fragments of the piston from the gears. I've tried driving down the frozen piston with a board and my BFH, to no success.



So, I'm stuck. The only possibilities I can think of are chiseling out the right piston to (possibly) free the crank, or cutting slots in the ends of the transmission assembly bolts to remove the transmission plate and extract the rest piece by piece. I don't know if any of the lower end parts are recoverable, but I'd like to get all the iron out before I recycle the lump.



Any other ideas?



Thanks,



R



P.S. As to what killed this engine, I wonder if it wasn't an assembly error, like under-torqued fasteners on the left conn rod. A number of things suggest that this was a low mileage engine. I believe the guy I got it from used it as a rear cover donor for the stator. Everything else appears to be undisturbed.
 

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holy crap i bet that was a loud noise before it locked up
 

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Yeah it looks like it's been abused/neglected a bit. Sometimes you win and sometimes you lose. At least if you get the covers off it that's $50 of free fun right there.
 

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I'd salvage what parts you can and dump the crank case.By the looks of it the bare minimum would be a re-bore and it will be cheaper to source another engine/block in good condition.With that kind of damage there are most likely micro-fractures in the cylinder walls and block that would show themselves down-the-line as an engine failure.

The crank and rods,even if they looked good,would be useless.



My 10 penn'th
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Discussion Starter · #6 ·
but at least it was a freebie and hopefully plenty of spare parts to be had

from the rest if it
Lots of usable parts.



I'll be using the clutch on the AdvWing, and it's already donated clutch springs to the Grub.



The front cover is pristine, except for the broken clutch cable holder, but I'll probably save it in case I ever do the hydraulic clutch mod I've contemplated.



Oil pump, chain and primary gear set all look good. I doubt it ran long enough after imploding to foul the pump, but it'll get a good cleaning anyway. I'd like to recover the transmission intact, but that may not be possible.



The rear cover is good, but the stator is almost black. These came off the '78 the PO was restoring. The output shaft has a broken flange, I suspect from the drive shaft being hammered off, rather than removing the bolt. The rest of the final shaft assembly looks OK, though.



The heads are questionable. The valves are all intact, but very badly corroded, one of the exhaust studs is broken off, and at least one receiver is split from a valve cover bolt being over-torqued. We'll see how they clean up.



I haven't checked the length of the cam chain, but from the small amount of evident wear in the case, I suspect it's almost new. The guides look good, and most importantly to me, the camshaft and followers are in good condition. The Grub is running a replacement camshaft with the original followers. It will be nice to have a matched set ready if that ever gives me trouble.



R
 

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Discussion Starter · #7 ·
I'd salvage what parts you can and dump the crank case.By the looks of it the bare minimum would be a re-bore and it will be cheaper to source another engine/block in good condition.
Agreed.



The left cylinder is badly scoured, and the right one probably will be, if I ever get that piston out.



The crank and rods,even if they looked good,would be useless.


The left rod is twisted about 5 degrees, so it's obviously scrap. The right rod might be OK, if it can be extracted, but I don't know that I'd risk it. The left journal on the crank is scoured, so that would only be usable if it were re-machined. $$$



R
 

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Agreed.



The left cylinder is badly scoured, and the right one probably will be, if I ever get that piston out.







The left rod is twisted about 5 degrees, so it's obviously scrap. The right rod might be OK, if it can be extracted, but I don't know that I'd risk it. The left journal on the crank is scoured, so that would only be usable if it were re-machined. $$$



R


I've been through this with many engine builds.Any engine that has seized will most likely have distorted the rods.This may be invisible to the naked eye.I've had all the rods I've used professionally checked by my local engineering/engine specialists(Yellow Pages).They threw away I think it was 2 of the 7 I gave them and they all looked good but they said those two had been twisted/stretched and take out-of-true even though they looked fine.



As there's quite a few good spares come up on Ebay pretty cheap it's not worth the risk IMHO.The crank in my present CX is from the US.I got it a few years ago when the Dollar was 1 to 1 with the Pound.

I've also recently got a set of low mileage heads from the US to fit to my other CX as a service point as it has worn valve guides and this worked out cheaper than renewing the valves and guides separately as I've done on my main ride.
 

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Randall,



I have an engine block sitting outside my garage that is going in for scrap. It is in better shape in the cylinders than that engine.



If you want the block for free I will put it back in the garage for you ...
 

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Discussion Starter · #11 ·
It was free right?
Yep. A guy reponded to my CL ad for the Spring Ride this past year, and said, "I sold my CX, but I still have an old engine. Do you want it?" I just had to go a couple miles to pick it up. I never actually met the guy. We had trouble connecting, so he just left it sitting outside his shop.



R
 

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Regardless of what you can salvage from your spare CX500 motor, exploded motor forensics is fun. You've inspired me to search for an old Polaroid photo I have of a bent connecting rod that I miraculously bent back into shape. That's on my '67 Honda Dream and it's still running to this day on that unbent con-rod. I bent it by going through a deep puddle and sucking in a big gulp of water.
 

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haha great! i have a 68 honda dream 305 that my dad bought new. it sat for 22 years and was all seized up. i used a pipe wrench on the crank and penetrating oil to free it up. i stood on the pipe wrench! and i've put 40,000 miles on that dream and it runs like a top!!
 

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i've put 40,000 miles on that dream and it runs like a top!!


Gotta Love A Honda... If the Apocalypse ever comes there will be 2 things left running; cockroaches and Hondas



You can Quote me for that!
 

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haha great! i have a 68 honda dream 305 that my dad bought new. it sat for 22 years and was all seized up. i used a pipe wrench on the crank and penetrating oil to free it up. i stood on the pipe wrench! and i've put 40,000 miles on that dream and it runs like a top!!


I love stories like that.It always reminds of that Volkswagen in the Woody Allen film,"Sleeper" in cave he finds after 200 years and it starts up<j/k>
 

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40,000 miles on a Honda Dream?!? Yipes, I find mine to be scary in the handling department so I only ride it maybe 80 miles per year. I stays in in the neighborhood and nowhere else.
 

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Discussion Starter · #17 ·
So, I'm stuck. The only possibilities I can think of are chiseling out the right piston to (possibly) free the crank, or cutting slots in the ends of the transmission assembly bolts to remove the transmission plate and extract the rest piece by piece.
I've thought of a third possible solution. If I can remove the crankshaft bearing holder off the rear side of the block, I'll have clear access to both nuts on the bearing cap to free the crank from the frozen piston. Only, I can't figure out how to extract the holder. The manual says to use a special tool on the front end of the crankshaft to press it out, but I'd need to remove the conn rod to do that.



Maybe I'll flip the block over and see if I can't get a wrench or a 1/4" ratchet to that far nut. Otherwise, I don't know what to do next.



R
 

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Soak around the end cap with some penetrating oil.Use a rubber mallet on the front end and tap a bit.Then very carefully and I mean carefully I use a couple of good large flat bladed screwdrivers to get under the cap areas I can as wedges and tap lightly to ease the bear cap up.It's takes patience and care this way as you can crack the end cap edges if not careful.There is also one area of the cap you do NOT want to lever which is the small thin flanged part.



The good news is that all CX/GL500 cranks are interchangeable and also the main bearings rarely wear or are damaged.Both my running engines have new big-end shells but I confidently re-used the main bearings e.g just left them alone.

Also and even though there are two sizes of main bearings the inner diameters are the same.They only made different ones because Honda made a couple of different batch runs on the crank cases and end-caps so they had to allow for the outer diameters of the shells to be different but the inner diameter and therefore all the cranks will just swap in without need to change the main bearing shells so long as the shell's white linings are in good condition.



FYI I always use Moly paste on bearing/cam-shaft/cam follower refits and also in my Rocker shafts.



Bookmark this page as it's a bible page for crank work,



http://www.engineparts.com/installationtips.asp
 

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Discussion Starter · #19 ·
Thanks, Shep. Good info.



R
 

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Discussion Starter · #20 ·
I've made a bit of progress since last posting here.



I managed to get an open-ended wrench on the right connrod clamp nuts, and to turn them in small increments. With the rod free from the crank, I was able to drive out the main bearing plate, which freed the left connrod clamp that was wedged between the crank and the transmission plate.



At that point, the trans came out easily. The transmission plate had been bashed in against the gears, but I have yet to disassemble it, so I don't know how much damage has been done there.



With the bearing plate off, I'd hoped to be able to pull the crank out past the right connrod, but it won't clear the counterweights. After a couple weeks of the penetrating oil soaking in, I finally managed to move the piston last night. With a little persuasion, it moves fairly easily below the point where it was frozen. I'll need to sand the rust off the cylinder walls to get it out, I think. Maybe I have a wire wheel that fits my drill?



R
 
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