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Hi. I'd just like to get some opinions on an issue I've had recently with my 1967 Honda Superhawk. I bought this bike not running a year ago and had to get the engine rebuilt. I had the cylinders bored, all new piston rings, piston clips and piston pins and gasket set. I was out of town and didnt ride it for 4 months. I've put between 500 and 1000 miles on this rebuilt engine. The other night I took it on the highway going about 60mph about 15 min. into the ride something went wrong and I lost a lot of power and oil was spraying all over the place. A friend took a look at it for me and said there was hardly any pressure on one side and there is scoring/ scratches on they cylinder wall.

My mechanic that rebuilt the engine says the piston had a heat siesure with little bits of piston that have stuck to the side of the cylinder walls. That is where the scoring came from. The reason for this was that the oil was pitch black and dirty and a little low. The oil was low due to it spraying all over the place though

Now I'll admit I had not changed the oil in a while but I don't understand how that could have caused this catastrophic failure. I think my mechanic is trying to avoid the blame for not having done a proper job when rebuilding this engine.

Prior to this incident my bike had been running great.

If anyone has an opinion on whether it's more likely that my shitty oil caused this problem or if my mechanic is to blame for not doing a proper job and is just trying to avoid redoing the work. Thanks
 

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First off welcome to the group. We like for folks to start out by introducing themselves in the member introductions section to let us know a bit about themselves and their bike(s). It would be helpful if you would include your location in your profile and create a signature with the model of your bike. And we really like pictures!:p

I personally would have changed the oil on a new engine a couple of times by now but even so, I don't believe an engine with less than 1000 miles on it failed like that because you hadn't changed the oil. I would be more inclined to believe the oil was black and dirty due to the ongoing wear and imminent failure. If it was the oil I would expect both cylinders to look the same.

Some of the more expert technicians here will be along to better assess whether you had a problem with a faulty part or maybe a less than great mechanic. If you can get it apart and get some pictures it would be helpful.
 

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I can think of a few things and have some questions to help narrow it down.

the main thing that could be your mechanic's fault is if he didn't give the new pistons enough clearance when he bored the cylinders.

you didn't say what pistons you bought or how much clearance you ran. I run a little more clearance than the book says to compensate for todays ethanol fuels. also forged pistons require more clearance than the stock cast pistons.

you also did not mention what caused you to have to rebuild the engine in the first place. was the oil pump bad
how are the bearings
are the oil passages clear of obstructions
take the motor apart carefully to figure out what caused the failure. measure and inspect all clearances.
 

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I would think the cause would be too tight a bore or excessive heat maybe from running lean or timing off. Hard to say for sure unless you have all the specs..piston clearance, ring gaps etc.

I agree with JT about oil... I don't think the oil would be the main cause but it would add to the problem as it breaks down due to heat. I change oil every 250 miles on a new engine even thou I run Syn T6 just to be safe.
 

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. . . The reason for this was that the oil was pitch black and dirty and a little low. The oil was low due to it spraying all over the place though.
From what part of the engine was the oil spraying -- head gasket, exhaust system, clutch push rod seal, broken case? That could shed some light on whether the engine failed due to lack of oil, or whether the oil was low because of engine failure.

Ray
 

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Discussion Starter #6
I'm not sure what pistons he put in there. I bought the bike not running and it turned out there was a hole in the piston the size of a quarter. Thats why it needed the rebuild. I do not trust myself to take this engine apart. I wouldn't do more damage than good with my little knowledge of motorcycle engines.

I can think of a few things and have some questions to help narrow it down.

the main thing that could be your mechanic's fault is if he didn't give the new pistons enough clearance when he bored the cylinders.

you didn't say what pistons you bought or how much clearance you ran. I run a little more clearance than the book says to compensate for todays ethanol fuels. also forged pistons require more clearance than the stock cast pistons.

you also did not mention what caused you to have to rebuild the engine in the first place. was the oil pump bad
how are the bearings
are the oil passages clear of obstructions
take the motor apart carefully to figure out what caused the failure. measure and inspect all clearances.
 

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Discussion Starter #7
The oil was coming from the crank vent. as soon as it gave me problems I took it off the highway and checked the oil. It was low but still within the appropriate range it needed to be. When I started it up again it started spraying all over the place and I think thats when it got low.
 

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Well, that sounds to me like things went south for your engine before the oil level became a problem, but it is still a guess. You have sort of a Catch-22 situation. It seems you are at least a little suspicious of the rebuilder, and that you don't feel like you have the experise to tear it down yourself. You could maybe have someone else do it, but that could get into a battle between him and the original builder, leaving you stuck in the middle. Sorry to hear of this misfortune, but I think outobie called it right. You can't really tell what happened without a careful teardown. Deciding if you want that done, and then finding someone to do it are probably your next steps. An alternative is to sell it as-is.

Ray
 

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Hi,

Did the mechanic only rebuild the top-end ? (engine cases were not opened ?) btw, why was it necessary to rebuild the top end ?

The reason depends on the above question. (I presume that you or your mechanic changed the oil after rebuilding the top end).

black oil after a short time : oil gets way to hot or/and oil is cleaning out the crankcases,

main reasons :

- to much advance (ignition issue), these engines are VERY sensitive, and a 5 to 10 degree over advance is enough to fit the description.
- fuel in the oil, the carbs of these bikes are known for this
- Using detergent oil in dirty engine cases, if the engine was not taken apart, the oil will clean the sludge out of the cases, and the sludge will clog the oilways, especialy the ones that cool/lubricate the cylinder walls and small end bearing.

There are more reasons, particular for these engines, but you have to give us a little more info on history and pictures,

Jensen

btw 1, is it a 1961 engine, or later ?
btw 2. was the oil spraying from the cylinder head crank vent also before the break down? Was the crank vent plate between the head and top cover mounted correctly ?
 

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You didn't happen to run of gas, while doing 60 mph on the highway, just before the engine tightened up?
 

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You said you rebuilt the engine because of a 'quarter size hole in the piston'. Was the cause for this condition addressed? Burning a hole in the piston is from HEAT. Either from a vacuum leak, lean fuel condition, or from overly advanced ignition timing. Your new piston also failed because of heat.........JMHO
 

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A good mechanic should have tried to figure out the cause of the original piston failure or let you know there may be issues...since it's not normal wear. If it has any mods like air filters, exhaust etc carb rejetting, plug chops will be necessary.
 

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So far my guess is that (we have very little info to do anything but guess)

the mechanic did exactly as he was told and fixed the damaged top end.

the issue is that our bike owner didn't know what to tell the mechanic to do (nor should he).

No one told the mechanic to figure out why the engine failed initially so the mechanic didn't. Since the original issue possibly still existed, the same issue may have caused the second top end failure.

unless something obvious is found in the motor (oops there's where I left that wrench) it will be difficult to blame the mechanic for not doing more than he was told to do (even though a good mechanic would have done so)
 

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Hi,

More responds on this thread are pointless and waist of time, since the OP signed in 05-01 for the last time.
Unless the OP responds and answers question, I won't spend more time on this thread,

Jensen
 

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I wouldn't abandon him so fast, not even a week yet....We all work and get busy....but i would wait and see what his responses are....He may not like the answers he is getting.


Like all problems, the root cause is the where fix lies. It's like a blown fuse. The fix is not replacing the fuse, the fix is find the short that caused the blwn fuse. A new fuse will just blow again.

To the OP, if you rebuild the engine again, it is likely you will just hole another piston again. After fixing the piston, you really need to find the root cause of the failure.

The issue for a melted or holed piston is always excessive heat. Heat is caused by improper mixture or timing. You have some info here to point your mechanic at a search.

Let us know what's going on...
 

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I covered the same ideas in my post , Richard, and still no reply.
 

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I covered the same ideas in my post , Richard, and still no reply.
Yep, Hoping a repeat of the same message might reinforce the concept...

Good ideas are worth repeating ;)
 

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I wouldn't abandon him so fast, not even a week yet.
No offence, not abandon ;) just taking a pause in responding untill there's more information, this way our answers / responses can be more specific and helpful,

Jensen
 

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Hi there. Long time no post.
In 2013 after a 1 over rebuild, I toasted Lucille (65 CB160) on the highway: WOT, 75mph and about 2+ miles down the road, exit to exit. Upon further inspection a few things appear to have been common in your rebuild failure, or were suggested as possible causes:
too much advance
too much time WOT without a chance for the pump to play catch-up
running hotter #6 plugs (didn't read them before I put them in) instead of 8's

All were a perfect storm waiting to happen.

I think it's more a matter of analyzing the circumstances of the ride that it happened on and diagnosing backwards. Maybe the "input" i.e. speed, ambient temperature, cleanliness of the oil pump, etc were the cause.

Personal experience, unless you are in race trim on the west coast, these little girls needs a little more love...

All the Best,
Andrew
 
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