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low rpm engine knock. Water in Engine?

  • Thread starter Thread starter Anonymous
  • Start date Start date
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Anonymous

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My bike was running perfect until I came back from vacation. I had left it with a friend and he rode the bike once during the 6 days I was gone. He said it ran great?

Then we got about 2 days worth of heavy rain (my bike has a cover but it is a cheaper one that lets water in). I came back from vacation and went to pick up my bike. Immediately I noticed that the battery was really very low on power. I could not get the bike to turn over. After popping the clutch in second gear we got the bike started BUT there was a very loud knocking noise coming from the engine. There wasn't much oil in the bike but I took care of that immediately (the oil light didn't go on either, and I know for a fact that it works). The knocking didn't go away at low rpm's but did if you twisted the throttle. I noticed that the bike would not stay idling by itself. Also, the throttle was VERY spongy, like the bike only had half the power it should.

The bike had been sitting for 6 days with about a quarter tank of gas. Since it rained a lot and for an extended period of time with no stopping could this be the cause? Water in the tank? Can water in the carbs cause an engine knock at low rpms? I also do not have a left side cover on my bike and the battery is exposed. Thanks for all help provided?.
 
First of all, make sure you don't have water in your plug caps. Make sure your bike is firing on all 4 (or 2?). What you describe sounds a little like the bike isn't running on all cylinders.

Water in your tank should not cause a knock, at least not a permanent one. It may cause the bike to run poorly and unevenly (or not at all), but that should go away once you have good gas in the tank and drained your carbs float bowls. I've heard of sugar in a gas tank causing bottom-end destruction however.

Not wanting to cast dispersions on your friend, but do you trust him? Is it possible he accidently over-revved the engine and blew out a bearing? I'd ask him point blank when he first heard the noise and check his eye contact :). It's just hard to believe so many things could go wrong with the bike with just one little ride.
 
yes he is very trustworthy. He owns a couple bikes himself and has helped me out on my bike a lot.

I'm just trying to figure out what to do about this. Trying to come up with some way of figuring out what the problem is.

I do think it is strange that a few weeks ago i had more than enough oil and then last night it wouldn't even register that i had oil in the window.

Any other comments or suggestions? It has to have SOMETHING to do with the rain....doesn't it?
 
1. Make sure all spark plugs are firing with a good spark. Maybe there's water in the caps as I said? Remove the plugs and look at them. Does one look like it isn't firing (wet, fouled).
2. Clean out the gas tank and carb float bowls and fill tank with fresh gas.
3. If this doesn't help, maybe you'll need to dismantle/clean the carbs.

You need to get the bike running well enough to make a determination about the knock. Maybe getting it running properly will fix it. If not... if it's a steady (evenly spaced sounds) knocking, it's a rod bearing. If it's more of a vibrating rumble, it's a main. If its an irregular knocking/slapping, it could be a lot of different things.
 
thanks very much for the reply, it does sound like a evenly spaced knocking. One more question though....if the knocking goes away when the engine is running at a higher RPM, does that still mean it could be a rod bearing? shouldn't the knocking get worse and faster as the engine is revved? Thanks again...
 
Once the bike is running OK, here are some tests for a rod bearing. I'm going to assume you have a 4-cyl bike. Remove one spark plug cap with the engine running and see if the noise goes away. Do this for all cylinders. If it goes away for one of them, that rod bearing is suspect. Next, find a wooden dowel about the diameter of a pencil. Remove all plugs and rotate the suspect piston just past TDC. Then push down on the piston crown with the dowel. If it moves at all - you have a bad rod bearing. You can also remove the oil pan to gain access to bottom end. If you do that, just see how much up/down play the bearing has. It should be virtually non-existent in a good bearing.

Generally a rod-bearing knock is louder at low RPM when the engine is under a load, like accelerating from a stop.
 
thank you for your advice. It is supposed to rain for the next few days. I will check everything after that I guess. Hopefully it has something to do with it just running crappy from the water....
 
Good luck. Just remember to eliminate the easiest things first.

Ace.
 
btw. if it is a rod bearing...is that something REALLY serious and costly?
 
Not knowing which model you have, it's hard to say what it will mean. The 4-cyl GS roller bearing crankshaft is not easily rebuildable. There are some out there with expertise to do it, but the cost is prohibitive. The best bet is to find an old engine or crankshaft at a salvage yard. The good news is that by and large, these crankshafts are virtually indestructable if taken care of.
 
thanks for the help.

i finally was able to work on the bike. I emptied the gas can and before filling with fresh gas I push started the bike with the tank off and let the gas run out of the bowls. The knocking went away by itself it seems. After reassembling the tank and filling it with fresh gas, it still wouldn't start on it's own. Another push start later and it was running very well. Took it for a semi-nice ride today to get the battery charged back up again. Came home and immediately tried to start it...no luck...let it sit for 3 hours and tried again...started right up. :)

looks like problem solved. it was the rain. must have been hindering my spark plugs firing properly...thus causing the knock....

thanks again....
 
Good - that certainly was the easiest thing :wink:

I never have problems like this because I don't ride in the rain unless I absolutely have to - and I live in Seattle!
 
I realize this sort of jumps past the problem tyler had with his engine, but going back to the possible bearing problems... there WILL be metal contamination in the oil filter if there is damage of any sort to the bearings. If bearing problems are suspect, pull the oil filter and open that thing up like an accordian and inspect it closely. If necessary, even dunk the filter in a small container with a small amount of fuel in it, slosh it around to wash out any metallic dust or fragments, then strain that fuel through a paint strainer and see what remains... aluminum, iron, babbit, etc. Knowing what contaminants you have will go a long way towards telling you exactly what type problem you've suffered.
 
whoops...looks like a few a new problem has developed....it appears my batter is acting a little strange....

the starting problems i was having are back. i can only get about 5 or 6 strong "sounding" cranks before the battery dies down....

after riding for awhile it is ok. and it keeps the charge that it builds up..but once it's time to start...same issue.

any suggestions? could the rain have perhaps drained the battery down to nothing and now the cells are pretty much dead?

i can pop the clutch and start it no problem...
 
Sounds like a bad battery. You can try charging it on a 2 Amp trickle charger overnight. Check the voltage before and after. If it doesn't go to and stay at 13.5 volts or more, it's gone. If it does hold a charge, your charging system is suspect. If that's the case, review that Stator Papers in the Garage section of this site.
 
haven't had a chance to throw it on the charger yet...

but here is another hint...

i walk started it again and rode it around for about 5 minutes (city driving...lots of lights and stop signs) to test out my front forks cause i changed the oil, don't think i got above 30 mph.

when i got back i tried starting it again and the battery was definetly almost dead.

if i kill the battery and then leave it for a few hours it charges back to a point where i can get those 3 or 4 slow cranks out of it....so does that mean that the battery is still by itself? how does it regain that little bit of power each time? does this also mean that it's probably the battery? i assume if it was an electrical problem that it would drain the battery dead with the bike just sitting there to the point where i wouldn't even be able to get a few cranks out of it...
 
Those are classic symptoms of charging system failure. You are sucking power from the battery to run the bike, so right after you run it the battery is at the lowest charge. Charging system failures are very common on these old bikes - usually starts with the R/R which in turn leads to stator failure.

An easy test is to check your battery voltage before you bump start it, and check it again after the bike is running. It should be 1.5-2 volts higher if the charging system is working.
 
ahhh yes BUT the other day i went on a lot longer ride on the highway (about 15 miles of 55mph) and when i got back the battery was very strong.....it was only letting it sit overnight that the battery was back to being weak....

so THAT would sound like a battery problem right?
 
ha ha...

ok....thats what i'll do.


sorry that last message was just me talking out loud i think. i will hook up the VOM tonight and see what happens...
 
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