hawkeyefxr Posted February 11, 2023 Share Posted February 11, 2023 For my sins i have embarked on an engine rebuild of a CM250 1981 model. I decided on this as the compression was down quite a bit at 125 psi. From the start it has been an uphill struggle, engine mounting bolts seized in the crankcases making it difficult to remove the engine from the frame. I now have the engine out with one bolt still seized but will get to that later. The barrells, and head are held down by eight ten mm wasted bolts, the wasted section is eight mm. As they were well and truly seized i drilled the heads off and removed the valve gear, head and barrels. I have a cam type stud extractor and though that would work, but no it would not grip the long bolts as they are incredibly hard. I bought one the the rollers type stud extractors but they don't grip either. I have 3/8 and 1/2 inch air guns but they do not help. I have tried heating the cases but I only have a turbo torch which is ok for brazing so pretty hot but as it's 6c here at the moment it's nowhere good enough. I will wait till it's warmer so there is not so much temperature difference when heating the crankcases though i think it will need Oxy/Acet torch. If anyone has any ideas i would be glad to hear them. I'm not exactly new to this at 74 and have been riding bikes since i was 14, i have also worked in a couple of bike shop in my younger years but never come across anything like this. So it's out there HELP!!! lol. Quote Link to comment Share on other sites More sharing options...
Old-codger Posted February 11, 2023 Share Posted February 11, 2023 I would find a big bucket and stick the engine in there and pour diesel over it until its an inch above the stuck bolt threads then leave it for a week or to. Take it out drain it off then give it a blast of heat and a tweak with grips. If it doesnt move back in the tank for another soak and repeat. It can take ages as the studs have been in there for years. Another way ive used is the stud will be scrap so shorten it to say an inch above the barrel face then using an arce welder weld on a big tight fitting nut. This puts a lot of heat in a small space hopefully breaking the bond of the bolt and cases and you can get a ring spanner on for a bit of leverage. Quote Link to comment Share on other sites More sharing options...
hawkeyefxr Posted February 11, 2023 Author Share Posted February 11, 2023 (edited) Unfortunately i only have the top end down, don't really want to strip the entire engine as my space is limited. I have just bought an old garage heater which should get the whole bottom end hot. If that fails then i will have to seriously think of your option. I had thought of welding a nut on there, as you say the intense does make the alloy expand greater than the steel. Edited February 11, 2023 by hawkeyefxr Quote Link to comment Share on other sites More sharing options...
hawkeye Posted February 19, 2023 Share Posted February 19, 2023 Just a quick update on the studs, i have one out thanks to the 'socket' type stud extractor, it has rollers inside and locks onto the stud. Unfortunately it broke on the second stud, my fault for buying a cheap tool. I now have to grind the bloody thing off. Quote Link to comment Share on other sites More sharing options...
Bender Posted February 19, 2023 Share Posted February 19, 2023 Pics the thread needs pics Cheap tools rarely work out well when things are stuck. Quote Link to comment Share on other sites More sharing options...
hawkeye Posted March 13, 2023 Share Posted March 13, 2023 On 19/02/2023 at 22:08, Bender said: Pics the thread needs pics Cheap tools rarely work out well when things are stuck. There not much to take a picture of at the moment, just a lot of bits lol. Found out the toll did not break. Still really struggling to get the last one out. 1 Quote Link to comment Share on other sites More sharing options...
Bender Posted March 13, 2023 Share Posted March 13, 2023 12 minutes ago, hawkeye said: There not much to take a picture of at the moment, just a lot of bits lol. Found out the toll did not break. Still really struggling to get the last one out. Keep at it, the small victories all add up Quote Link to comment Share on other sites More sharing options...
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