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Old 10-21-2010, 10:58 PM   #1 (permalink)
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knocking problem

Maybe someone can help me understand my knocking problem on my 94 evo flhtcu.

About 2 weeks ago I noticed when the rpms were about 2500 and I rolled the throttle on, the engine was giving me this small knocking noise. So, I back off just a little and it goes away, the rpms are still climbing and the noise goes away. But if I give it half throttle, it returns.

Well, lately, even if the rpms are up (3500) and I roll the throttle on, it KNOCKS REALLY LOUD!! I can't open the throttle all the way, even if I am going down hill. I haven't checked the timing yet, but I'm wondering why all of a sudden it just happened. Also, my mpg has dropped 3 to 4 miles. I am running the voes. Thinking that is the culprit. How do I check the switch?? Thoughts and suggestions would be well received.

Alan

80" evo bored .010
100 thousanths off the stock heads
ev27
cv carb
single fire coil
I forget what brand ignition, but it has adjustable curves

Last edited by bigbadal; 10-21-2010 at 11:03 PM.
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Old 10-22-2010, 08:28 AM   #2 (permalink)
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Maybe a collapsed lifter??? Just a guess.

My '95 EVO did some rattling but the gurus decided it was just the normal EVO noise of an air-cooled engine (no water jackets to dampen the noise).
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Old 10-22-2010, 04:30 PM   #3 (permalink)
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Nitram_b4 is reading this now saying WTF is this?
could be a lot of things, mostly not good
could be a bad wrist pin, more often than not a knock is a bottom end problem, I would not run it until it is figured out
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Old 10-22-2010, 07:16 PM   #4 (permalink)
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I agree with Nit b4, not good. How many miles on the ticker? Check the compensating sprocket, they are known to become loose and cause a racket.
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Old 10-22-2010, 07:44 PM   #5 (permalink)
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Quote:
Originally Posted by Nitram_b4 View Post
could be a lot of things, mostly not good
could be a bad wrist pin, more often than not a knock is a bottom end problem, I would not run it until it is figured out
Whoa. I hadn't thought of a wrist pin. The noise does sound like it is coming from the combustion chamber. Crud. Thanks for your reply.

Alan
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Old 10-22-2010, 08:43 PM   #6 (permalink)
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Quote:
Originally Posted by kwizard View Post
I agree with Nit b4, not good. How many miles on the ticker? Check the compensating sprocket, they are known to become loose and cause a racket.
I only have 9500 miles on the top end rebuild.

It's my understanding that the compensating sprocket will clatter at idle. Hmmm.
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Old 10-23-2010, 12:35 PM   #7 (permalink)
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Unhappy

Well, I found the problem. To me, who has limited hearing, it sounded like a knock, but it probably was a popping sound. The head gasket on the rear cylinder was letting the compression by due to the head bolt being loose. I haven't taken anything apart yet, but probably the threads in the case are ruined and will have to be fixed. Will likely due all 8 holes for both cylinders. Good time to happen, just started raining here in southern oregon.
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Old 10-25-2010, 12:29 PM   #8 (permalink)
Len
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Usually if your head nut gets loose it means that the stud is pulling out of the crank case, I hope it isn't that going in.
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Old 10-25-2010, 11:09 PM   #9 (permalink)
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Quote:
Originally Posted by Len View Post
Usually if your head nut gets loose it means that the stud is pulling out of the crank case, I hope it isn't that going in.
Yes, I do believe it probably is pulling out of the case. I tried to tighten it up, to no avail. It won't stop moving, and I'm only pushing on a 7 inch wrench with both thumbs. I will tear it apart this week and see what the problem is.
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