BobbyBreeze Posted July 4, 2010 Share Posted July 4, 2010 Thought i'd start a thread where engine building tech questions can be asked and discussed. I've got a motor I'm slowly gathering parts for with a piston / rod combo that looks like I'm going to have around 50thou (1.25mm ish) big end side clearance. Is this going to pose an issue? Small end side clearance can be what I want (rod is getting machined down to fit into piston). Engine will be a revver and get thrashed, later on probably in competition. Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted July 4, 2010 Share Posted July 4, 2010 I'm no expert Rob. (Depsite what I might say when I've got a belly full of diesels ) But with lots of side clearance, might that not allow the oil to leave the big end bearing too quicky? Would not the side clearance with the standard A series set up slow down the oil's exit from the bearing? just a thought. Quote Link to comment Share on other sites More sharing options...
Hemi Posted July 4, 2010 Share Posted July 4, 2010 i was kind of thinking the same thing .. but what if the rod had too much clearance and moved enough to block the oil feed to the gudeon pin?? . bit far fetched as the bearing oil feed hole are pretty forgiving ... just somthing to think about though?. Quote Link to comment Share on other sites More sharing options...
Roman Posted July 4, 2010 Share Posted July 4, 2010 Aahh so you're talking about the clearance from the big end of the rod, to the side of the block? I'm guessing you're not talking about the clearance of the big end bearing shell to the crank if it's 1.5mm If that was the case for me, I'd shave another mm or two off the side of the block, just in the areas where it's looking close. What kind of engine is it, 4 cyl? If it's something really oldschool with less than 5 main bearings for the crank then yeah it might be a concern having the middle rods wobble a little closer to the edge of the block hahaha. If it's got a main bearing each side of each rod, I dont see how it could really flex all that much I guess? Unless the block is flimsy or something. Quote Link to comment Share on other sites More sharing options...
Yowzer Posted July 4, 2010 Share Posted July 4, 2010 If it's got a main bearing each side of each rod, I dont see how it could really flex all that much I guess? Unless the block is flimsy or something. In which case ya shouldn't be using it for track use in the 1st place. The only issue I can see is if something fucks up, it'll fuck up a bit more epically. Quote Link to comment Share on other sites More sharing options...
BobbyBreeze Posted July 4, 2010 Author Share Posted July 4, 2010 I'm no expert Rob. (Depsite what I might say when I've got a belly full of diesels ) But with lots of side clearance, might that not allow the oil to leave the big end bearing too quicky? Would not the side clearance with the standard A series set up slow down the oil's exit from the bearing? just a thought. Thought about this, but i think its the bearing shell to journal clearance that regulates the oil flow out the bearing. If you think that this clearance is much tighter than the side clearance to the crank web? Aahh so you're talking about the clearance from the big end of the rod, to the side of the block?I'm guessing you're not talking about the clearance of the big end bearing shell to the crank if it's 1.5mm Nope, talking about clearance from big end shell to the crank web. D in this photo. Strictly its not the shell to web clearance as in these rods the shell is slightly recessed from the side of the rod. This kind of leads me to believe the clearance isn't important as long as its not too tight. Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted July 5, 2010 Share Posted July 5, 2010 I may well be wrong Rob, it was just a random thought that sprang into my head. Another thing that also just sprang into my head is that you'd have smaller bearing area too. Quote Link to comment Share on other sites More sharing options...
Testament Posted July 5, 2010 Share Posted July 5, 2010 I would be reluctant to try it with an engine that I had spent much on. But I have heard of this type of thing before as SBC rods are almost identical to fiat twin cam rods except for that dimension, and there is a huge amount of relatively cheap forged rods available. Unfortunately I haven't seen any concrete evidence of something actually running an engine with such a setup. go for it on mule engine maybe? Quote Link to comment Share on other sites More sharing options...
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