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Post by flu on Jun 27, 2013 4:07:30 GMT -5
Just trying to see how many people put a 50mm or 52mm kit on and had the crank fail on them. I keep reading that it WILL ruin a stock crank but I haven't read anyone posting that it has.
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Post by indymoped on Jun 27, 2013 4:31:26 GMT -5
More power=More wear and tear on the crank. Depending on how you ride it may last a long time or it may last a very short time. On average i think most people get 2000-3000 miles out of a crank after a 50mm BBK install. If you want a long life span on your crank go with a smaller BBK
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Post by carasdad on Jun 27, 2013 5:00:56 GMT -5
We have 2 with them..one is over 5,000...the other over 6,000. What eats them up..is improper install. Folks will slap one on and end up with a compression of 240psi and have seen even higher  !! Starter cannot crank it...and I could BARELY kick it over. Needles to say on both..the cranks did not last...nor did the pistons. The detonation..heat caused by it and super high compression made the flat top pistons bowl shaped excessively. When built ours we added an extra base gasket and head gasket. This kept the pressure about 180 psi...and not a single issue in their 5,000-6,000 miles.Bottom line...a little common sense and mechanical knowledge go a long way. ;D |
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Post by buford1488 on Jun 27, 2013 5:25:02 GMT -5
this is why we cut the combustion chamber now at scrappy's..........
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Post by flu on Jun 27, 2013 6:18:14 GMT -5
carasdad were you running a stock head on those or big valve heads?
buford1488 what do you mean cut the combustion chamber?
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Post by buford1488 on Jun 27, 2013 6:32:12 GMT -5
like this....to lower the compression Attachments:
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Post by buford1488 on Jun 27, 2013 6:34:13 GMT -5
sorry dont know how to reduce the pic..........
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Post by buford1488 on Jun 27, 2013 6:39:48 GMT -5
may be this is a better pic......... Attachments:
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Post by carasdad on Jun 27, 2013 8:12:27 GMT -5
carasdad were you running a stock head on those or big valve heads? buford1488 what do you mean cut the combustion chamber? Stock head with the extra gaskets...or with scrappydogs head you don't need them...just standard gaskets as they cut a relief area in the head to lower compression. |
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Post by larry001964 on Jun 27, 2013 8:32:14 GMT -5
We have 2 with them..one is over 5,000...the other over 6,000. What eats them up..is improper install. Folks will slap one on and end up with a compression of 240psi and have seen even higher !! Starter cannot crank it...and I could BARELY kick it over. Needles to say on both..the cranks did not last...nor did the pistons. The detonation..heat caused by it and super high compression made the flat top pistons bowl shaped excessively. When built ours we added an extra base gasket and head gasket. This kept the pressure about 180 psi...and not a single issue in their 5,000-6,000 miles.Bottom line...a little common sense and mechanical knowledge go a long way. ;D I would have to agree with this, My first stroker was improperly installed ( no extra base gasket installed ), and it did exactly what Carasdad explained.. My compression was 205, and it did to the piston exactly as Carasdad explained.. I take the blame for this, getting in a hurry to assemble my engine instead of waiting for the right parts. I also had a 52 jug with a 50mm head, further raising compression.. At the time I could not find a 52mm big bore head.. Yep I agree with him completely |
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Post by carasdad on Jun 27, 2013 8:40:48 GMT -5
may be this is a better pic......... This what happens to the piston when compression is too high. Larry's was 205 as he said...this guys scoot I fixed was 235-240. Look at the bowl shape of the piston in the following 2 pics. Attachments:
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Post by carasdad on Jun 27, 2013 8:42:26 GMT -5
[replyingto=carasdad]carasdad[/replyingto]Here is another view. Once we got the compression at or below 180..we later checked the piston after 1,000 miles. Looked fresh as new..  Attachments:
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Post by larry001964 on Jun 27, 2013 8:46:32 GMT -5
Yep here's the actual compression at the time..  |
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Post by buford1488 on Jun 27, 2013 8:48:27 GMT -5
yep with the head cut like i do it's 180-190. with out being cut it's gonna be over 200 if the valves dont leak..with big valves.
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Post by millsc on Jun 27, 2013 9:53:40 GMT -5
Safer to use two gaskets with scrappys big valve heads if made by buford they have zero leak compression is higher he makes them very high quality
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