Rod Knock Question.

[sgd37]

Hi everyone,

I am restoring a cb500 k1 and I am having all sorts of trouble with it. Its my first project and my first 70's SOHC so I don't know much that isn't in the manual. I rebuilt the carbs and managed to get the engine ticking over but only on cylinders 1 and 4 (the PO electronic ignition has failed). It sounded pretty rough but I wonder if there isn't something worse like rod knock going on. I've attached two videos, one at idle and one with some throttle.

I'd appreciate if someone could tell me if that sounds normal for two cylinder running.

https://youtu.be/3LkOl59bio4

https://youtu.be/68vvZk5DunM
cheers

[hairygit]

Yep, these old fours sound really awful with one cylinder down, let alone 2! DO NOT continue to run it like that, uneven forces on the crankshaft, can also be drawing petrol into the cylinders that aren't firing, which will run down the bores, washing off the oil, and causing horrendous wear to the bore and rings. Also, it will dilute the engine oil, causing terrible wear to anything that relies on it, crank, cam, valves, gearbox bearings..... do I need to go on?

[sgd37]

Thanks for the reply.

I had it started 4-5 times for 30 seconds or so each and only one more time for 5 seconds after the throttle video. Do you think that would be enough to cause damage?

When I checked the oil after running it had a faint whiff of petrol but surely the engine can handle a little flooding. The engine is off the frame so do you think it worthwhile to open it up?

Thanks again

[Bryanj]

If it actually was rod knock you will need another crank with at least one rod as they cannot be reground. Hondas do not do well with petrol in the oil and definitely not with petrol washed bores.

500's do suffer with primary chain wear which can terminally damage the crankcases as there is no tensioner, with the engine already out you are looking at maybe 2 hours to remove the lower case and check properly whilst also checking the selector forks which are also known to wear. You will need a gasket kit and time 

[sgd37]

I thought these bikes had a bullet proof reputation.

Fair enough I'll take the lower half off. Or maybe rebuild the entire thing and have peace of mind. Didn't think this would be necessary with only 22 000 miles on the clock

Cheers

[Trigger]

That means the clock has done 22000, the engine may have done a lot more. I specialise in SOHC engines and would advise a full strip to see what is going on.

[hairygit]

These engines DO have a bulletproof reputation, and indeed they are, BUT only if maintained properly with regular oil and filter changes, oil is the lifeblood of these engines, and fail to change/ check regularly will rapidly do terminal damage!

[sgd37]

Well I am going to rebuild the engine. Even though I don't think it needs it (I haven't run it for that long and I did put oil and new filter in it before I did anything). There are stories of these things running on less cylinders on the road and coming out fine or am I misinformed.

Anyway better to know exactly what the state of the internals are so I don't have nasty surprises later on.

Cheers for the advice

[Bryanj]

At 22000 I would fit a new primary chain, cush rubbers in the primary gear, new seals and cam chain anyway, don't forget all that rubber is 40 years old anyway.

The big cost is time and with the engine already out that is halved

[matthewmosse]

Looked after these engines can be very very tough, I have put 180,000 miles on one with very little work needed, but regular oil changes, and not thrashing it at high revs for any length of time. Conversly I have bought them with very low claimed milage and seen engines which are far more worn than mine was after the stellar milage it covered. As has been said, the engine is out, probably worth having a look. I used to just bung em in with fresh oil, filter and service and run as they were, but prices have gone up and up, no longer are decent engines to be had for the price of a gasket set.