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| Crank grinding? https://www.slantsix.org/forum/viewtopic.php?t=33813 |
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| Author: | zorg [ Mon Feb 16, 2009 10:21 pm ] |
| Post subject: | Crank grinding? |
Searching and reading prepping for my first engine build, starting to go crazy from all the info. One question I haven't been able to find an answer for. Can someone please explain Doc's recommendation to grind the crank .010 under for torque improvement? Thanks in advance. |
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| Author: | Doc [ Tue Feb 17, 2009 9:49 am ] |
| Post subject: | |
Uhmmm... where did you read that? Regrinding the crank .010 under is common to clean-up the journals and often the racers will grind the oil clearances a little wider so the engine spins a little easier... The only torque influance you can gain thru crank grinding is if you off-set grind the crank to get a little more stroke and compression. DD |
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| Author: | zorg [ Tue Feb 17, 2009 5:42 pm ] |
| Post subject: | |
I read it in Aggressive Ted's build info. Offset grinding for more stroke would require new con. rods, and a host of other changes, right? Another question: What are the advantages to boring .030 over, rather than just rehone and rering? Other than spending more money... |
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| Author: | DusterIdiot [ Tue Feb 17, 2009 6:15 pm ] |
| Post subject: | Depends on how you look at it... |
Quote: Another question: What are the advantages to boring .030 over
This is a question that has a couple 'ins and outs' on it...1) .030 over nets you more cubes (not much of a real gain there in the 225 realm though....LOL) 2) getting the bores realigned, bored and honed if done right gains you better sealing with the rings...if you just rehone and rering, it becomes a 'compromise' especially if you take your bore measurements and you have a slight 'egg' to the bore also if you take the measurements and find the bore is way outside the spec for a re-hone you'll be re-boring anyway for the next step up anyway... I would never recommend knurling the pistons if you were doing a 'po-boys' rebuild.... 3) bigger bore may allow you to unshroud the valves a bit more if running bigger valves so they get proper flow when off their seats... This all depends on what you are intending to do with the engine, if just band-aiding it along as a daily driver with some weekend abuse you might get away with a rehone if everything looks good spec/measurement-wise... taking the time to do a quality job front to back...it pays you back in reliability and enjoyment later... -D.Idiot |
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| Author: | zorg [ Wed Feb 18, 2009 2:17 pm ] |
| Post subject: | Re: Depends on how you look at it... |
Quote: especially if you take your bore measurements and you have a slight 'egg' to the bore also if you take the measurements and find the bore is way outside the spec for a re-hone
Yes, that question was based on everything checking out.Quote: This all depends on what you are intending to do with the engine, if just band-aiding it along as a daily driver with some weekend abuse you might get away with a rehone if everything looks good spec/measurement-wise... taking the time to do a quality job front to back...it pays you back in reliability and enjoyment later...
As a carpenter, I totally understand doing a quality job the first time around. Yes, it will be a daily driver with some weekend abuse. But I like to overbuild everything, so no band-aiding. I do plan on using engnbldr's O/S valves. Since my ignorance is already quite apparent, if .030 over is good, is .060 or .080 over better? I recall reading .100 is max over bore. Thanks a ton, the motor should come out tonight!
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| Author: | Doc [ Wed Feb 18, 2009 3:45 pm ] |
| Post subject: | |
The goal is to have round & straight cylinder bores that stay that way during operation. (head torque, heat expension and cylinder pressure "spikes" all work against this goal) The 'rule of thumb'... just overbore the amount needed in order to clean-up the cylinders at the next available piston / ring size. Keeping the cylinder walls thick, helps them stay round and straight. Many shops will bore larger then needed because they do not have to be as careful in getting their equipment perfectly centered and straight. They use "bigger is better" logic. In my opinion, a good, stable ring seal will make more power... more power then you get from adding a few extra cubic inches of displacement from the bigger bore size. DD |
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| Author: | zorg [ Fri Feb 20, 2009 1:22 pm ] |
| Post subject: | Thanks! |
Thank you both for the schooling! The engine came out last night almost as if I knew what I was doing. A reputable machine shop has been located. Cam selection is narrowed down to 2 choices... (Erson 270, or Doc's 260/244 RDP grind). Things are moving right along, and I am getting excited. Back to searching the archives! |
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