Best w&d grit grade to polish up crank journal
Discussion
Need to fix this crank journal before the next race. Obviously new rods and block will be needed as the former came out through the side of the latter but I think the crank is salvageable. I'm thinking a quick lash over with 80 grit and then some 240 or 360 to polish it up. Any other suggestions?
On a more serious note it sounds like a bit of a mystery this case. It's a full monty Vauxhall XE in an Escort rally car. Dry sump, forged pistons and rods, just over 250 bhp on the engine dyno. Not sure who the original engine builder was but it was completely reliable I'm told albeit getting a bit old and smoky. It got sent off for rebuild to someone who's acquiring a good reputation for rebuilding engines these days. Another std block was sourced because the 2 litre class limit precludes any reboring. Spent 4 hours on the dyno being run in and power tested, everything looked fine, 75 psi oil pressure, seized No3 big end bearing on its first event, span the shells, buggered the crank, that rod and some of the valves.
Back for an emergency rebuild in the three weeks before the next event, another std crank sourced, new forged rods, back on the dyno, everything looked fine, 75 psi oil pressure, 4 miles from the start of the first stage No3 big end goes again resulting in the unwanted ventilation of the block as pictured.
I have been asked to ponder what could make the same No3 big end keep blowing up as soon as the engine is fitted to the car when it seems to run fine on the dyno. It seems an unlikely problem for a dry sumped engine to have and the XE is famously reliable. No3 big end is fed from the centre main so I've suggested someone have a look at the oil feed drillings to that journal as this fresh block is a common denominator but little else springs to mind, especially without being able to examine the bits.
Back for an emergency rebuild in the three weeks before the next event, another std crank sourced, new forged rods, back on the dyno, everything looked fine, 75 psi oil pressure, 4 miles from the start of the first stage No3 big end goes again resulting in the unwanted ventilation of the block as pictured.
I have been asked to ponder what could make the same No3 big end keep blowing up as soon as the engine is fitted to the car when it seems to run fine on the dyno. It seems an unlikely problem for a dry sumped engine to have and the XE is famously reliable. No3 big end is fed from the centre main so I've suggested someone have a look at the oil feed drillings to that journal as this fresh block is a common denominator but little else springs to mind, especially without being able to examine the bits.
Edited by Pumaracing on Monday 3rd August 21:32
My Facebook message to the guy involved earlier today covers that very point.
"Seems strange that it's reliable on the dyno but fails immediately in the car. Is there anything about the installation that could possibly differ materially from the dyno setup?"
Nothing springs to his mind. The installation hasn't changed since he bought the car with the original engine in which ran fine for the two events he did with it before the first rebuild. I asked yesterday if there was any sign of det either in No 3 or anywhere else but am told there is not.
"Seems strange that it's reliable on the dyno but fails immediately in the car. Is there anything about the installation that could possibly differ materially from the dyno setup?"
Nothing springs to his mind. The installation hasn't changed since he bought the car with the original engine in which ran fine for the two events he did with it before the first rebuild. I asked yesterday if there was any sign of det either in No 3 or anywhere else but am told there is not.
Edited by Pumaracing on Monday 3rd August 22:04
I doubt I'll get to see the bits in person. The owner lives a fair way off I'm told, I don't know him, I only know the navigator. The event it blew up in was held abroad but I believe the car is back home now and the engine out. Some things may be discernible from good pics but the engine builder will probably want to see it all intact without someone else stripping it down. I certainly would if I was being held to a warranty. Mind you, with damage that severe maybe the cause of the problem has already been obscured.
It's a hard pill to swallow though when that many expensive new shiny bits get destroyed after 4 miles. It would be nice to know why and have a definite solution for the next build. With the same problem twice in quick succession one would hope that a cause could be determined with sufficient expertise.
It's a hard pill to swallow though when that many expensive new shiny bits get destroyed after 4 miles. It would be nice to know why and have a definite solution for the next build. With the same problem twice in quick succession one would hope that a cause could be determined with sufficient expertise.
Hmmmmf. I'm getting peeved now with the story I'm being told and how it keeps changing. I said in the first place when I was phoned on Sunday morning that this is almost certainly a lubrication problem despite the supposed 75 psi on the gauge but I've only just found out a few minutes ago that the dry sump system was all brand new on the first rebuild and then it was all re-used on the second rebuild that only lasted 4 miles. But that apparently wasn't important enough to mention to me previously!
If I now understand correctly the previously reliable dry sump system that came with the car was retained with its original engine and what I was informed was a rebuild was actually everything new from scratch but to be honest I'm still not sure.
I sent this message on Facebook yesterday to the navigator.
"I also wonder if your oil pressure gauge setup is working right because the oil pressure would have vanished as the big end failed - before it seized anyway. You said the driver saw it reading 75 psi right up to the end but I'd be very surprised at that."
A digital gauge I'm told which I'm slightly suspicious of but given this new information that the whole dry sump system was also new immediately prior to the two blow ups I suspect we've found the root of the problem. I have my doubts that the reading of 75 psi was actually 75 psi.
I went into this in great detail on the phone on Sunday that where on the block the oil pressure is measured at makes a difference and just because the pressure is X at some point in the system doesn't mean it's still that high by the time it reaches the main bearing journals if there's some sort of restriction in between. I was told that the pressure reading is taken right next to the dry sump pump which I dislike as it's better to read it from the middle of the main oil gallery alongside the crank.
If I now understand correctly the previously reliable dry sump system that came with the car was retained with its original engine and what I was informed was a rebuild was actually everything new from scratch but to be honest I'm still not sure.
I sent this message on Facebook yesterday to the navigator.
"I also wonder if your oil pressure gauge setup is working right because the oil pressure would have vanished as the big end failed - before it seized anyway. You said the driver saw it reading 75 psi right up to the end but I'd be very surprised at that."
A digital gauge I'm told which I'm slightly suspicious of but given this new information that the whole dry sump system was also new immediately prior to the two blow ups I suspect we've found the root of the problem. I have my doubts that the reading of 75 psi was actually 75 psi.
I went into this in great detail on the phone on Sunday that where on the block the oil pressure is measured at makes a difference and just because the pressure is X at some point in the system doesn't mean it's still that high by the time it reaches the main bearing journals if there's some sort of restriction in between. I was told that the pressure reading is taken right next to the dry sump pump which I dislike as it's better to read it from the middle of the main oil gallery alongside the crank.
The depth of the hard case on a nitrided crank is the unknown variable here. It's unlikely to be more than about 20 thou on radius unless the crank spent a hell of a long time in the nitrogen. It takes like 2 or 3 days at 550C just to get 20 thou. Then some of that will get used up during the final grind to size, usually about 5 thou leaving maybe 15.
So hopefully enough to get a 10 thou diameter undersize out of it without renitriding or maybe even two grinds of 10 thou.
But, the next issue is how much of a problem is it really if you use up the case depth? Cast iron cranks are soft as muck. EN19B cranks aren't hardened at all. Only EN40B nitriding steel is.
So in conclusion I'd say it's ok either way.
So hopefully enough to get a 10 thou diameter undersize out of it without renitriding or maybe even two grinds of 10 thou.
But, the next issue is how much of a problem is it really if you use up the case depth? Cast iron cranks are soft as muck. EN19B cranks aren't hardened at all. Only EN40B nitriding steel is.
So in conclusion I'd say it's ok either way.
PeterBurgess said:
I've seen this on a few dry sumped engines especially Pinto circuit ones. Fine on the rollers or engine dyno then fail on the track. In all the ones we have come across and helped find the problem, the cause was slight leak on dry sump system so when going round bend (usually long sweeping bend, only left or right if side pickup) the leak area was subject to air ingress as the oil was pulled away under cornering forces. Engines died instantly with bearing failure. Same as when a wet sump is not baffled sufficiently.
Peter
Where about in the system are you meaning by "leak"? In the external pipework or somewhere internal?Peter
PeterBurgess said:
Internal Dave. One bloke with a 2.4 Pinto lost his engine three times, he had a miniscule leak on a joint in the scavenge pipe in the sump which just sucked air on long right hand bends, was perfect on engine dyno and on our rolling road.It was 25 years ago but I remember it cos the bloke was so gutted each time it failed 
We have seen problem about half a dozen times altogether. Heartbreaking as engines so expensive and all seemed fine just to be dashed on the track. Have even seen hairline cracks in pipes. Not saying it is so in your mate's case. Maybe problem with the new dry sump set up though? Seems to have the familiar ring to the failure, interesting to know if they had just come out of a long bend or in a long bend when it failed and any similarities with driving for both failures? Shame anyhow.
Peter
Thank you for that info Peter. They're reading this thread so hopefully someone will check all this out properly if I don't get asked to be involved. I've already told them it's vanishingly unlikely to be a fault in the dimensions of either the conrods or crank journals and 99% sure to be a problem with either oil pressure, oil flow, oil aeration or oil temperature. I now find out there was no oil temperature gauge fitted which is a bit of a false economy with so many expensive bits in the engine. We have seen problem about half a dozen times altogether. Heartbreaking as engines so expensive and all seemed fine just to be dashed on the track. Have even seen hairline cracks in pipes. Not saying it is so in your mate's case. Maybe problem with the new dry sump set up though? Seems to have the familiar ring to the failure, interesting to know if they had just come out of a long bend or in a long bend when it failed and any similarities with driving for both failures? Shame anyhow.Peter
Another question which I have no personal experience of answering. I'm told the last failure was only 3 or 4 miles from the start of the first stage. How long would it take a 250 bhp engine to bring the oil in a dry sump system up to normal temperature and maybe well above that? I assume the engine was fully warmed up before the start at least as far as water temp was concerned.
Bits from a Renault Clio 197 that went bang at the same event. The two things at the bottom are gudgeon pins I'm told. I've never seen gudgeon pins flattened and split right open before. Mind you I tried to build engines that didn't blow up rather than vice versa so I don't have much experience in this area. 
Update.
With only a week to go after the blowup until another rally last w/e the owner and my mate the co-driver frantically bolted the old bits from the various donor engines back into the car while an autopsy on the broken bits is planned for the future. The original bored out block that came with the car, the old dry sump system of identical make to the new one in the two blow ups and whichever head hadn't been used in the new rebuild.
It all ran like a champ all w/e with sustained 8500 rpm no problem. It points to something very obvious in either the block or dry sump system that let go twice and hopefully someone will discover what that was eventually.
With only a week to go after the blowup until another rally last w/e the owner and my mate the co-driver frantically bolted the old bits from the various donor engines back into the car while an autopsy on the broken bits is planned for the future. The original bored out block that came with the car, the old dry sump system of identical make to the new one in the two blow ups and whichever head hadn't been used in the new rebuild.
It all ran like a champ all w/e with sustained 8500 rpm no problem. It points to something very obvious in either the block or dry sump system that let go twice and hopefully someone will discover what that was eventually.
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