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Discussion Starter · #1 ·
k, so I got a 300ex engine with a bad crank and top end. I bought a complete 250x engine with a fresh rebuild with the intention of putting it in the 300ex but as i was bolting it in I noticed that the idiot overtightened damn near ever side cover bolt and cracked the case in several spots. So my question is, can I put the 250x crank and top end in my 300ex bottom end?? And basically end up with an electric start 250?
 

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Welcome to the Forums..... and to answer your question .... NOPE sorry the 300ex ceank is longer on one end. just find a 250X side cover cheaper than a crank kit.
 

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Discussion Starter · #3 ·
Well its not really the side cover. The case itself (where the screws for the side cover screw into) is cracked. I would be taking the rod and top end from the 250 and putting it in the 300 so the rod length shouldnt be relevent. Id be using a 250 rod and 250 top end..............
 

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But you said you wanted to change the crank? Is the crank toasted in the 300 engine or is the connecting rod? the rod lengths I believe are alittle different because the 250X is 57.3mm stroke and the 300 is 65.5mm the bore is the same though 74.0 mm
 

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the wrist pin height on the piston is the same for the 250x and 300ex. This is why the big bore kits will work for either one. The 300ex uses a shorter rod to allow for the longer stroke. As far as the "mechanic" over tightening the bolts and cracking the case, i haven't seen this. sounds like the holes were stripped and someone tried to use a slightly larger bolt and cracked them. i don't know how picky you are, but if it were me, i would go to autozone or advance and get a heli coil kit and drill and retap the holes to the proper size if possible. it would save a lot of work and headache as long as the cracks are not on the inside to where it could leak oil. i know it sucks, seems like every engine i get has stripped threads somewhere.
 

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That sucks dude!!!!!!!! I got my 250x and ripped into the engine, and during reassembly, I noticed that I missed/overlooked the head bolts. One was short, and one long- boy was I piised. I had to drill out the broken head bolt, after trying to retract a broken easy out. What a nightmare huh. Well went to install the rocker case to the head, when to my surprise-BAM-Half the rocker case bolts would not rethread and hold. I used Perma-coil inserts in all the stipped bolt holes,purchased kits off of ebay with way cheaper prices than the local auto stores. All bolts are still holding up good. Good Luck I feel your PAIN.
 

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Discussion Starter · #7 ·
No the threads are fine. Someone just had no sense of how tight to go with the bolts. The case itself is actually cracked around where the bolts thread into the case. So I either get some of that bondo type stuff for engines or replace the case. And about the pistons............I have a 300ex piston sitting on my work bench next to a 250x piston and the wrist pins are clearly in different spots. So how is this possible if they are the same??
 

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the piston bore is the same you may have a modifyied piston for a stroker crank? all I know is the piston is the same.
 
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