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Recently changed a head gasket on my 1200,and ran it out of time and bent 2 valves, when I pulled the head again, I see the marks on the top of the pistons left from the valves hitting. How do you know if the pistons are still Ok, anyway of telling ?

Cheers Bob
 

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well as long as the pistons arent majorly damaged with tons and tons of hits

i would just take some sand paper and smooth off the dings so you wont have any hot spots on the piston
 

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I'm with Peterbuilt, polish the piston tops and put it back together. Don't feel like the Lone Ranger ether.

Steve
 

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I am not sure on this because I am just an amateur wannabe Bike mechanic. But..if they are hitting the pistons it seems to me it may be an indication of something else wrong.Change the belts recently or have you done them? If not I think I would start there and get everything lined up. I could be just blowing smoke but it just seems like a place to start.:waving:
 

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Thanks appreciate the help, I'll do just what you said. I had the cam out of time and hadn't realised it. Picked a the wrong day to do it, my head was miles away that day.
Thanks again guys.
Cheers Bob.
 

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ceasefire49 wrote:
I am not sure on this because I am just an amateur wannabe Bike mechanic. But..if they are hitting the pistons it seems to me it may be an indication of something else wrong.Change the belts recently or have you done them? If not I think I would start there and get everything lined up. I could be just blowing smoke but it just seems like a place to start.:waving:
CF,

He said he ran it out of time, that's how the incident occurred.



Petebuilt/Sky Pilot,

If you have a good ding and grind off the material that got pushed up by the valve. Wouldn't the thinner metal in the void cause a hotspot on the piston and possibly blow thru. It doesn't seem like it would take much of a variation for the heat to seek out a weak point. The piston relies on even heat across the surface to function properly.
 

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no it wont cause any issues by smoothing off the rough spots or a ding there is plenty of meat on that piston i wouldnt be worried at all ive done this on cars, bikes, lawn mower catipilars, cummins ect im not the least worried aobut a .001 more thinner metal area it'll be fine

or split the case and replace pistons,
 

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Thanks PB, I was just curious about that. I don't know how thick the piston face is on that bike or how deep of a gouge is acceptable. Maybe after he grinds down the face he should measure the depth of the deepest gouge and somehow try and verify (sure as hell not by me..:smiler:) with you guys or a local mechanic (high school vocational places area good place to get info like this) to see if it's within a safe enough spec to run like that.



He would prolly have to find someone who knew the thickness specs of the piston to compare and access the damage. This way he may get a better idea of what he has without tearing everything apart.



I don't like doin extreme stuff, but when it all consists of just trying to verify what you have, it can't hurt.Blowin a hole or crackin a piston could be catastrophic to the engine.



Al
 

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I believe my answer would be:

Polish the pistons and try to forget it.

If the damage was bigger than we thought, following the piston failure, just drop in an exchange engine. Much easier than splitting the thing and doing pistons. But - that's me.

(for the damage to become piston failure, I'd think it'd need serious running mis-timed).

oh, and for the OP - I sure know the problem - head miles away - yet still trying to concentrate on a job. Yeah. Been there, done that.
 

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Okay didn't see on this post where he said he had it out of time. I guess it was another post. Sorry about that.
 

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Well, since enough people seem to know what they're talking about on this issue (AKA, not me), I think i'd polish the piston and run it. This was very interesting.
 

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nessy357 wrote:
Thanks appreciate the help, I'll do just what you said. I had the cam out of time and hadn't realised it. Picked a the wrong day to do it, my head was miles away that day..
After looking at the video and instructions for that job elsewhere on the site, I can easily believe you. It looks like you need to be fully alert to tackle timing belts on a Goldwing.
 

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Timing marks can sometimes be difficult to see even under the best of conditions.

I always recommend to anyone starting this job to make there own timing marks with a dab of paint in a easily viewed location prior to loosening the belts. This will ensure the belts are timed exactly as removed. No guesswork about being a half tooth off or if viewed from a different angle.

Hope this helps other members here contemplating the replacement of belts.;)

JD
 

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Just asking because I don't know, but would there be any chance of valve damage? Would a compression test show this?
 

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yea valves are probly bent. lay head fkat on back valves facing up and fill with solvent if it leaks throw valves they are probly bent.

it will run with bent valves but not well.
wilf
 

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I agree with just polishing the dings or marks if thats all it done., and there is enough meat to do it back when we raced we actually cut depressions half moon sorta on stroker motors.
 

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wilf wrote:
yea valves are probly bent. lay head fkat on back valves facing up and fill with solvent if it leaks throw valves they are probly bent.

it will run with bent valves but not well.
wilf
There is no question that the valves are bent. The best course of action would be to replace the ones that hit and then lap all of them.

Steve
 

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SuperSkypilot wrote:
....The best course of action would be to replace the ones that hit and then lap all of them.

Steve
I had a bad valve in an 1100 and the book said NOT to lap them in, but have the head cut to match the new valve.





Bill
 

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I wonder how they assume cutting the head will work? When you lap the valves in, you're matching the valve and the seat in for a perfect fit.



I wonder how long he had the engine running before he shut it down and realized what happened.
 

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Predator wrote:
I wonder how they assume cutting the head will work? When you lap the valves in, you're matching the valve and the seat in for a perfect fit....


Who is 'they'?



I had it done once and it was fine. A dealer did the cutting, no lapping, and I checked it with solvent before installing the head; no leaks or issues. The cost was less than what the head gasket was, so why risk doing something they say not to do?



Bill
 
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