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Discussion Starter · #1 ·
Lost my first engine ever this weekend after having buit my own for almost 20 years. Just curious what you guys think may have happened. It is a 740+hp 406 SBC 18° heads. I am turning it to about 7900. First off here is what I know. #6 rod is in multiple pieces broke about 1" below the wrist pin pin/small end still move ok no evidence of heat there. The #6 journal is black and severly trashed like something was welded to it and then forcfully removed. #5 is dark as well and the bearing was beat up. All the other rod bearings look ok except for some having evidence of trash going throug them. The cam wont turn (probably bent) and it sheared the teeth off the timing belt (Jesel) It bent a couple pushrods and broke one in two. It appears all the exhaust valves have made contact with the pistons. although they still appear to be sitting flat against the seats I havent pulled the last couple rods or the crank yet I am still pretty sick its going to be a while before I have the cash to replace all this stuff. I just want to see what I can find out about it to prevent it if possible in the future. I usually put about 300 passes per season on my car and it usually gets freshened every winter. We had a baby last year so I only put about 140 passes on it and decided not to pull it down last winter. It was on its 271st pass when it let go. The rods had 1 prior season on them and we upgraded to L19 bolts and had them resized last time it was apart. No warning other than it didnt rpm like it usually does. The oil pressure was good when I staged. Because the journal is black I am thinking an oiling problem or something happend to the rod to get it mishapen. The thing that puzzles me is why #6? its pretty much in the middle of the crank. Odd thing is I did crack a stock block in the bore years ago using this same crank and it was #6 cyl as well. The crank has been maged and checked for roundness each time it was apart with no issues. A buddy of mines dad works for a company that builds polishing equipment for the big 3 and some of the larger crank companies. He took the crank into work and had it polished to within 40millionths of being perfectly round with a 1ra surface finish. So I know the crank was right. The rods were eagle H beams. I will post pictures when I can get them uploaded to a host.

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Craig
 

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Craig, one thing comes to mind when I read that you busted a H beam rod and had upgraded to L19 bolts.
Did you torque the bolts or check the stretch when you installed them? L19 hardware is great but I know 2 guys that lost motors because they torqued them and never check the stretch. If the big end comes loose the crank pin is like a hot dog in a hallway.
 

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Discussion Starter · #3 ·
At the time of the last rebuild I tore the engine down and everything looked sweet. I could have literally reused the bearings and rings. I had thought about replacing the rods with a better unit but my machininst figued unless I was ready to really step up to a big $$$ set of rods the additional cost didn't warrant going to a middle of the road rod. They were the last remaining "cheep" (read chinese) component left in the motor. As a comprimise we decided to upgrade the bolts. The rods had about 300 passes on them since new. My machine shop installed the L19 bolts in the rods and rechecked them. Either because of the new bolts or just the # of runs on them they decided to resize the big end to make them right. I am pretty sure they used a stretch gauge on them when they resized them. I however just used a tourque wrench when assembling the motor. Hindsite is 20/20 maybe I should have spent the $$ on new rods.

Craig
 

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With the crank discolored it was a bearing failure. Werther it be from inadequate oil supply or to little clearance. Sounds like to me when you changed bolts and had the big end resized, they might have been slightly smaller i.d. than before, therefore tightening up the bearing clearance.

I guarantee the rod broke because it wasn't able to spin on the rod journal after seizing up.
 

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At this point it might be hard to tell which went first but in the future do yourself a favor and check the bolt stretch not just torque the rod bolts, it might save some dollers and headache later on. The L19 hardware is great but must be tightened correctly to be effective.
 

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From what you say something went wrong with the bearing on 6 and it sounds like oil issues or size issues. Something made it hurt that bearing then the rest was the result of the rod breaking. JMO, RM
 

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Discussion Starter · #7 ·
With the crank discolored it was a bearing failure. Werther it be from inadequate oil supply or to little clearance. Sounds like to me when you changed bolts and had the big end resized, they might have been slightly smaller i.d. than before, therefore tightening up the bearing clearance.

I guarantee the rod broke because it wasn't able to spin on the rod journal after seizing up.
I agree the rod seized on the journal and thats what broke it. As far as the clearances go I know for a fact they were dead on that is one thing my machine shop is meticulous about. They were if anything a bit on the loose side. When the crank was polished it did end up on the lower limit of STD. All the rods were checked we ended up using a std and a .001 over bearing on them to get the clearance right. this has been the way we did the bearings since I first started using this crank in my previous motor. I pay my machine shop to set the bearing clearances for me as I dont have the best measuring equipment. The only other variable to toss in there is I did recently switch from torco to sunoco race gas but it looks more like a oiling/clearance issue than a detonation deal. Like I mentioned all the other rod bearings I checked looked good and fit in the rod/cap like they were supposed to.

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Craig
 

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Discussion Starter · #8 ·
For some reason I cant get my putfile account to upload pictures. I can email some out if someone can post them up here

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Craig
 

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Discussion Starter · #10 ·
went to imageshack said something about not currently accepting new accounts
 

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Any signs of detonation in it? It will pinch the rod bearing in and then scrape the oil off the crank and look just like that
 

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Discussion Starter · #14 ·
Any signs of detonation in it? It will pinch the rod bearing in and then scrape the oil off the crank and look just like that
All the other rod bearings looked good no signs of pinching and they fit in the cap/rod like they did when new. Most of the ones I have seen with detonation issues looked like they were flattened at the top and bottom and kind of "curled up" and acted like they were too small to fit in the rod/cap correctly. These had none of those signs

Craig
 

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Discussion Starter · #17 ·
Yeah I am sure the bearing and rod were installed correctly. The bearings were H series so there was a specific lower and upper along with having to mix a std and .001" over to get the right clearance. I tripple checked them when puting it together. This motor wasn't something that just went together either it made 270 flawless passes prior to grenading #271 well that is one I would like to forget what a sick sound. Last time it was all the way apart was back in February of 2007 I wouldn't think an assembly error would take that long to show up anyway.

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Craig
 

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Discussion Starter · #18 ·
You are in the same boat as me, but mine gernaded after 7 passes. The issues I had was the builder built it to tight.

http://www.picturetrail.com/sfx/album/view/19910166
Yeah looking at your pictures there are some similaritys mine doesnt appear to have tagged the valves as hard as yours did. My crank journal also got alot hotter before it let go its really really ripped up with lots of metal transfer. When I can stomach it again I will go over and finish pulling it all the way apart and take some more pictures.

Craig
 

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The crank got real hot..... the bearing was burning up for a while before the failure.... it's an oiling/clearance issue - likely.

Did you recheck clearances, or did you assume since the engine was run before that the clearances were good?
 

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Discussion Starter · #20 ·
The clearances were all rechecked by my machine shop (I paid them to do it) at the last freshen up when we replaced the rod bolts and resized the rods. These guys typically set them up on the loose side I have the specs on my build sheet but I havent pulled it out to look at it yet. I run my motors fairly cold I warm it up idling around the pits until I see 160° coolant temp and the oil pressure typically drops 10psi or so once the oil thins. I then let the motor cool until first round where I typically start the burnout @ 140° I was runing mobil1 15w50 and typically had 50psi hot. On the dyno this year the oil pressure wasn't stellar especially when the vacuum pump was pulling a bunch(hadnt adjusted the regulator to 12" yet) . here is the dyno sheet showing oil temp and pressure.

 
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