threw another #3 rod, how to prevent this from happening again. |
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threw another #3 rod, how to prevent this from happening again. |
crash914 |
Oct 29 2019, 03:17 PM
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#1
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its a mystery to me Group: Members Posts: 1,826 Joined: 17-March 03 From: Marriottsville, MD Member No.: 434 Region Association: MidAtlantic Region |
So blew up my #3 rod. wondering what caused this. lack of oil, due to rpm? poor return? oil pump sucking air?
last time it was #2 rod. I really don't want to live with this again. Motor specs, Dual oil coolers with full flow plumbing 102 bore by 80mm stroke long rods, ham heads and valve train. Running to 6800 rpm g loads to 1.5 windage tray modified at pushrod tubes for oil flow tuna can with 1/2 extra oil Pics of horror below. First are this failure, then old failure. |
Mark Henry |
Nov 1 2019, 12:46 PM
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#2
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
To me 6800 rpm is really pushing the limits of a stroker T4.
You have a number of fail points that can be happening all at the same time, below I'm only addressing crank flex. Crank flex the crank actually bending at/near the center main journal, as well the 2" "chevy" rod journals. Having 2 throws without support in between the rod journals is another weak point. the higher the RPM the more flex. This flex is why a 1.7/1.8 case is a better choice over a 2.0 case, as the crank flexes even in a stock engine and it's hard on the center main case bearing saddle. VW knew this, basically stating a 2.0 couldn't be done reliably and it was Porsche that designed/modified the 2.0 crank for the '73 914. VW didn't use the 2.0 engine in the bus, till the 914 proved it was satisfactory reliable enough, for the 1976 model year. With a longer stroke, in this case a 80mm, at high rpm you are amplifying all the bad, the crank flexes, causing bending stress on the rods, points of the bearings begin touching the crank journals, side loading, heat begins to spike, add into the mix events high RPM downshifting causing mechanical over rev, etc. All of these stress points begin to cascade as RPM increases until the weakest point fails, in this case the rod. I'd choose the 78mm crank with T1 rod journals just because the bigger T1 journal has more strength. I'd also lower my redline to no more than 6500rpm. Hope this makes sense, I've got a L5 herniated disc back issues and I'm whacked out on pain meds. |
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