1972 CL350 K4. Engine seizure - next steps.

[CarloMécano]

So I was riding for a last time in early november 2024 - cool day, end of season in Canada. I was getting to a town close to home, when my engine seemed to start getting really hot, making a different sounds, when climbing up a sloped road going over the freeway , the bike suddenly seized, wheel locked up and i slid to a stop. I put the bike in neutral and walked the bike to the nearest gas station , and my father came with my truck and a bike rack to pick it up. It was my last ride, and since i have only stored it in my father's shed , removed the tank , seat and battery .

My question for the folks is: what are my next steps to get this bike running? I'm thinking of seeing if it was lack of lubrication, checking to see if i can unstick the engine while in the frame (making sure i don't have any issues with timing or a valve sitting on a piston). Any chance from experience out there that this is not a major fault with the cam system or sprocket? (I have had a sprocket bolt snap due to improper torque and engine fall out of time and seize before - i hope this is not the case)

My idea is to pull off cam covers , assuring everything is ok valve timing wise, take off side cases, inspect + clean oil filters, oil sump etc. pull out spark plugs to inspect cylinder holes for anything odd. From there add some marvel mystery oil to soak up a while and attempt to rotate engine afterwards. if successful drop oil add fresh oil, and see if i can run and check head oil pressure through inspection bolt to see if i have oil getting to the top of the engine head.

Anyone want to add some insight ??? tips or recommendations ? anything is appreciated. Spring is coming !
I will be returning home from Mexico early May , So I will get to it then an dcan keep the thread updated on what i find and what happens.

Love this bike, hope i can salvage it and get it running again.

Cheers.
Carlo.

 

[stl360+450]

I would take a peek into the spark plug hole to see what the pistons look like. I blew up a motor once on the highway and I also believe it was oil starved. I will include a picture of the worst piston below.



In my opinion, the best course of action is to dismount the motor and do a full teardown. It's hard to check everything carefully without taking the motor apart.

Your bike looks great. I'm sure you'll be able to get it going again.

 

[CarloMécano]

I would take a peek into the spark plug hole to see what the pistons look like. I blew up a motor once on the highway and I also believe it was oil starved. I will include a picture of the worst piston below.

View attachment 56913

In my opinion, the best course of action is to dismount the motor and do a full teardown. It's hard to check everything carefully without taking the motor apart.

Your bike looks great. I'm sure you'll be able to get it going again.

Wow clearly lacked some lubrication eh? , ya i guess you are correct. Better make sure and tear down to inspect. I heard it easier to rotate the engine and free it up prior to taking it out of the frame and putting it on the bench. fingers crossed it will be ok. cheers.

 

[ancientdad]

So I was riding for a last time in early november 2024 - cool day, end of season in Canada. I was getting to a town close to home, when my engine seemed to start getting really hot, making a different sounds, when climbing up a sloped road going over the freeway , the bike suddenly seized, wheel locked up and i slid to a stop.

Certainly sounds like an oil-starved situation as already mentioned. Had you checked the oil before that day's ride? These air cooled engines consume a little bit of oil as a way of life, so it's best to check the oil before every ride to be sure it isn't critically low. If you're on a long, all-day ride over a distance, you should check the oil at every gas stop too. Also, did the bike have a large oil leak when this happened? The clutch rod seal on the 350 is known to blow out of the crankcase at times too, which causes immediate catastrophic oil loss if not noticed right away.

 

[stl360+450]

Anyone want to add some insight, tips, or recommendations? anything is appreciated. Spring is coming!

This could be a great opportunity to replace every seal, clean out the crankcases, and rebuild with fresh gaskets everywhere. Ordering a full gasket kit (with seals) ahead of time would be a good idea.

Unfortunately, you won't know how the cam bearings, cam, followers, pistons, and cylinders look until you get it apart. I have sometimes purchased replacement cylinders and pistons ahead of the teardown so the rebuild can be done without additional delay. This is more beneficial when the bike is currently running to minimize downtime and doesn't really apply here.

 

[Boomer343]

From your description the engine seized hard, very hard if the rear wheel skidded. Last one I did that seized at highway speeds was from the blown seal AD mentioned.

I seriously doubt you will get away with anything less than a full rebuild. I had to cut the cam chain and never did get one of the cam supports off the cam even with a three pound hammer .... had it out of the engine by this point. I replaced the whole top end, head, cylinders, pistons cam, cam chain .... everything including the mechanical advance which showed discoloration from heat.

BTW it was the cam that seized, the pistons didn't seize in the bores but were certainly affected by the heat.

 

[J-T]

I have seen an air cooled engine seize from lack of lubrication then start right up after it cooled off. Granted, it was a POS lawnmower engine but still.............................

If this is the case invest your paycheck in lottery tickets.

 

[OMF]

Sorry to hear about your engine troubles. The way it seized up on you, I think you’re in for a full rebuild. On my parts engine I had to soak the cylinder in diesel, and use a wooden block that was shaped to fit in the bore, and then use a 5 lb sledge hammer beating on the wood to free it up. It took about 2 weeks, beating on it every other day to free it up….hopefully you’ll have an easier time with yours.
You have a great looking bike there, and it’s definitely worth putting in the effort to get it up and running again.

 

[CarloMécano]

This a spare engine i have , in case i need a part from it. Mind you it is in very rough shape and it is very seized.

 

[guzziart]

Drop the oil. if there's metal (shavings to chunks) in it you're in for an engine rebuild (or good used one...may be less expensive). Good luck, sad to hear of about your 350.

 

[KickStart]

I don’t know if the 350 will do the same, but retarded timing will heat an engine up till seizing. When I got my first Triumph (‘63 T100) , I took it for a ride from the Bay area to the foothills above Sacramento. It seized up a couple of times, but restarted once cooled. When I got to my destination, I checked it over. What I found is that the timing was retarded. The points & timing on the old Triumphs was complicated, and apparently dynamic. Once timed properly, it ran well for months until I gave as a gift to a friend. I think the Triumph Twin is more forgiving than a Honda Twin.

 

[guzziart]

I don’t know if the 350 will do the same, but retarded timing will heat an engine up till seizing. When I got my first Triumph (‘63 T100) , I took it for a ride from the Bay area to the foothills above Sacramento. It seized up a couple of times, but restarted once cooled. When I got to my destination, I checked it over. What I found is that the timing was retarded. The points & timing on the old Triumphs was complicated, and apparently dynamic. Once timed properly, it ran well for months until I gave as a gift to a friend. I think the Triumph Twin is more forgiving than a Honda Twin.

Yeah, that'd be great if Carlo gets back here with a good outcome.

 

[CarloMécano]

Yeah, that'd be great if Carlo gets back here with a good outcome.

Here we are . Left side piston is seized at wrist pin. Not floating at all . Causing it to seize and would not rotate. Also signifiant wear damage visible from heat or friction on left side of cam lobes and rocker arms.


My right side piston is floating on its pin properly.


Anyone experience this before?? Lack of oil issue? Or carb running too rich over time creating excessive heat?

Thanks. I have gaskets and seals ordered for early june delivery

 

[ancientdad]

Based only on that picture, my first thought would be gummed up crankshaft oil passages not delivering enough upward splash to the pistons as it should.

 

[boddy]

Those pistons and rings were recently replaced. The lower skirt of the piston looks brand new and the oil ring is the newer 3 piece style. I agree with AD that it is likely a plugged oil passageway.

 

[CarloMécano]

Yeah, that'd be great if Carlo gets back here with a good outcome.

Here we are . Left side piston is seized at wrist pin. Not floating at all . Causing it to seize and would not rotate. Also signifiant wear damage visible from heat or friction on left side of cam lobes and rocker arms.


My right side piston is floating on its pin properly.


Anyone experience this before?? Lack of oil issue? Or carb running too rich over time creating excessive heat?

Thanks. I have gaskets and seals ordered for early june delivery

View attachment 57920

Based only on that picture, my first thought would be gummed up crankshaft oil passages not delivering enough upward splash to the pistons as it should.

fair point.

So further teardown recommended? Or is there a way to check fluid flow ? Cleaning procedure?

 

[boddy]

I think a further teardown is warranted. You'll want to check your crankshaft and make sure the passages are clear. There is a thread on this mostly for the CB450 crank but the 350 is similar.

Crankshaft Cleaning

I've been following all of the build threads on this site and seeing the damage that foreign debris in the oil can cause I started to get paranoid about properly cleaning the crankshaft of my 71 CB450. In Teebo's most recent thread 12ozPBR mentions cleaning the flywheel area near the main...

www.vintagehondatwins.com

 

[ancientdad]

So further teardown recommended? Or is there a way to check fluid flow ? Cleaning procedure?

Unfortunately, a complete overhaul (both top and bottom end) is necessary if the crankshaft passages are plugged, no way to get to them without complete removal of the crankshaft.

What he said above.

 

[CarloMécano]

I have been taking apart a spare k3 model cb engine i got for 100bucks a while ago. As the k4 has been damaged on the parts lacking lube and grinding. So far with patience i think we will have success salvaging our way to a running engine.

This got me re-assured. Even if an engine sits outside for ages. The insides coule be well worth the investigation.

Just look at that cam and rockers. Sprocket never touched it seems. Nice

Keep yall posted
Cheers

 

[stl360+450]

What we can see inside the donor motor looks good. The side cover looks polished/chromed and there are hex head bolts on the side cover and rocker box, so I'm guessing someone was taking a good interest in that motor at some point. Too bad it was outside, apparently without the points cover!

I'm glad to see you posting about this rebuild. I would encourage you to post more and share the progress step by step.

What's your current plan? Are you going to use parts from motor #2 in motor #1? Or will motor #2 be rebuilt and become motor #1?

 

[guzziart]

I have been taking apart a spare k3 model cb engine i got for 100bucks a while ago. As the k4 has been damaged on the parts lacking lube and grinding. So far with patience i think we will have success salvaging our way to a running engine.

Sounds good if you know what is interchangeable between k3 & K4....I personally do not.

 

[stl360+450]

I believe these two motors should be more or less interchangeable, in part or whole.

I would recommend splitting the cases on both motors. Choose the better one to rebuild. This would allow for a good cleaning of the cases and crank, replacement of all seals, and a thorough inspection of the transmission.