A few of you may remember a few weeks ago when I busted some pushrods. While at the drag strip, at the staging lanes a horrible tapping sound started coming from my engine so I backed off and was able to limp home. The tapping only lasted about 15 seconds and I couldn't see anything under the valve covers so I drove home. It ran fine on the way home and then I took off the intake and rocker arms to find 3 busted pushrods.

So I decided to go ahead and pull the engine out, tear it down and inspect based on my own gut feeling and advice from Lars. Well, I was hoping to find everything OK, maybe send the parts off to a machine shop and have them re-balance everything and throw it back together. Well, this day I'm not so lucky. Here's what I found:
Broken Piston, Cylinder # 8

Crossing my fingers I flipped over the head to unfortunately see this:

Here are some closer pictures. It appears that the noise I heard was probably actually the piston breaking and being chewed up. I saw this because all of the damaged parts have no burn spots on them....they look fresh.


The cylinder wall looks and feels good so at least that's a good sign.

Here is a shot of the good cylinders, a lot of oil burning going on.


So, am I totally screwed or is there hope for an inexpensive recovery? Can the head be fixed and relatively cheaply? As for the piston, I can always buy a replacement piston and have it balanced to match the rest, I'm not too worried about that. I'm worried about the head and the true cause. Was this detonation or could it have been caused by the pushrod breaking? I can't imagine it was the pushrod's fault cause the valves still look good, indicating pieces didn't get past the valves. And I just can't see how little tiny pieces of a pushrod could cause this. I guess it could also just be a failed piston...manufacture defect.

 

Man......I feel for ya.

I'd be calling Mark at AR and see what he thinks.....it can't hurt.

 

it doesn't appear that the bore is scratched but you need to put your finger in there and check.

I would take the head to a machine shop and tell them to shave it 10 thousandths to see if it will clean up.

then put a new piston in it and put it back together.

detonation usually causes the ring lands to break.

 

The pushrod bending was a result of the valves hitting the piston chunk. As what caused the ring land to break, I don't know.

 

I thought I had some bad luck but you're worse than me. Is this the same engine you had the oil pan rail clearance problems with a few months back??

Brett

 

Nope, that was somebody else.

 

Oops, my bad. Still sux about your motor...

Brett

 

I think it is important this is shared with the forum and applaude u showing broad shoulders to post this.
Yes that looks like the result of detonation that we all read about as i see no valve marks on any of the piston pix. Doesn't look fatal for the block but i would no longer trust those pistons and that compression ratio. Be careful that bad cylinder maybe out of round and have it checked. If low miles maybe just scrub the block with hot water and Tide or Borax at the car wash using bottle brushes to clean the passages. Utectic pistons are cheap but strong enough and a lower c.r. would be recommended. If no deep sratches can be felt in cylinder wall then just a clean up with a hand hone should do. But spend the money and recondition the rods - shot peen & new bolts - then balance the assembly. Crank probably fine. Most hardware stores sell a flex shaft tool for grinding (much bigger manchine than Dremel Tools) and clean up the sharp edges in the cyl head yourself. Most cylinders heads vary in camber size (cc volume) unless reworked and not a big worry there. Use a pushrod checker tool and get the p-rod length right.
Yes u can take it to a shop and have it all perfected or at least told so but hey that motor wasn't a big $ build to start with (and i won't bad mouth anyones choice now) so why not use it to learn. Only shop work i think u really need is rod recon and assembly balance. What im saying is why not use the good parts u have to rebuild a low miles block for <$700. Only parts needed are pistons, bearings, lifters & p-rods and gasket set unless u want a different cam too.
BTW i hear Eh Ain't Ready (oooops) has quite a backlog on custom engines - let alone returns. :o
Good luck. cardo0

 

 

Cardo0, I definitely plan on using all of the good parts to put this thing back together. And I'd like to do all the work myself that I can. But do you really think ALL pistons need to be replaced? And why the lifters? I've already got the new pushrods and I just bought the same size as what was in the motor. Also, going down in compression. I think it's only currently at about 10.85-1 right now. I'd rather not go down in compression and also rather not replace all pistons. Am I trying to have my cake and eat it too?

 

The broken push rod problem, I purchased the 74 convert. that Bgrice had for sale last year in Pearland with the Ar Racing 355 in it. I got the car running and finished it up, Put it up for sale when I got my 92 convertible. I sold it to a person at a swap meet after putting about 250 miles on it. It ran good for me but did seem to smoke a bit when started. After I sold it I got a call about a week later and was asked if any thing had been changed with the cam from the orignal build, I told him that that is the way it came from AR Racing. He said that while driving down the road it started making a lot of rocker noise and he took it in to a shop, they found broken pushrods on one cylinder and a possible bad lobe on another. I asked him to keep me updated on the outcome of it but I never heard from him, He also got the orignal engine from me to the car and said he was going to put it back in to make more of a daily driver out of it for his wife.

 

SERIOUS BUMMER. E-mail those pics to Mark Lim.

 

I'm curious to know what piston they put in there. Did the timing chain slip? What would cause the piston to break like that?

 

What kind of pistons are those? Is that an aluminum or iron head? Were you using nitrous? Your oil consumtion may have been caused by improper intake to head alignment. Had the block or heads been cut?

 

Damn

Just a question.. Do you run a rev-limiter???

 

Well the $700 question is what caused the piston to bust? Will it happen again? What condition is that cylinders rod in? Yes u may be able to locate the correct piston and now is a great time to verify c.r.. This would greatly reduce costs. And if you measure everything (micrometer) to it acceptable it would return to service. But for how long?
I remember a couple of guys that used to have a ball racing and abusing thier firebird until the motor busted. They used to advance the cam by just advancing the cam sprocket 1 whole tooth at a time. I remember them swapping motors once a month and they enjoyed it - so did the local engine supplier.
But a machinist friend of mine built his 383 with only 8.8 c.r. (just by parts coincidence) and has now 4 racing seasons with it reaching the 10s. Granted it only wieghs 2,200 lbs and is a race only C3.
So if you want to try the same piston at least pull that cyl rod and have it inspected. Also check that cyl bore for round and taper - cylinders have a taper specification too. Check the quench hieght too but i don't see any piston marks on cyl head. U need a quench hieght of about .040"-.050" to reduce effects of detonation. Using extra thick head gaskets only reduces helpful quench effects and the lower c.r. reduces power/torque. And thats why i mentioned new pistons but just my 2 cents here. For less than $300 utectec dished pistons that reduce c.r. are what im talking 'bout - reducing c.r. but not quench.
Hang in there and take ur time. We're hoping for a happy ending to this story. cardo0

 

Man...bummer Travis...

Hate to see that.

Well, I can tell you what I'd do if it was mine. For sure I would step up to a forged piston. I think for the compression you want, the fact you have a four speed and some gears and like to run it hard, along with TX heat, the chances of detonation are pretty good. Not sure what RPM you twist that thing to, but anything out in the 6000-6500 range is pushing it for even good hypereutectics. Lots have done it, but they don't handle rpm well for long. If one died, the others are very suspect too. Also,any oil in cylinder just makes it more likely to happen.

I would really check the cylinders and try to get by with just honing them. They will need to be slightly looser anyway with the forged pistons, so likely you won't have to bore it all over again.

You can get a pretty good idea of rod condition by looking at bearings closely. Any twist will show up on them. Unless you found an issue, I wouldn't worry about them all too much except for the one that took the pounding. But really, it doesn;t cost much to have them checked/resized.

The head can easily be cleaned up. But with all that metal beating around in there, it's very likely that some of it had to go past valves. I'd get them touched up too. Send me an e-mail...I might be able to help you with that part if you would like.

So we're talking new forged pistons, rings, bearings gaskets along with machine work as needed. Might need to eat that generic food for a while huh?


JIM

 

Either that or the ends of the top ring butting together because they were too tight to begin with. Were these hypereutectic pistons?

 

You've all got some good questions and recommendations. I just got done completely tearing the motor down a while ago but have to prepare for a presentation at work Tuesday. It's out of town so I'll be gone for a few days. When I get back I'll answer all your questions.

I can tell you that I found where the oil consumption was coming from. On top of the valve guides there are teflon seals. All but 2 or 3 of them where broken. They actually have cracks in them and you can see some wear on the outer retaining sleeves. It looks as if maybe the springs rub on them on the inside and maybe make them bind and the teflon seal splits. I'll take some pictures when I get back.
Here's a few answers for now:
Timing chain didn't appear to slip although I had forgotten to check the timing after installing a new intake just before heading to the track and when I checked it at the track before racing it was way off. I can't remember if it was too advanced or retarded. Anyways, I set it at about 36 degrees at 2500rpm.
Heads are Canfield aluminum heads.
No nitrous.
Don't believe pistons are forged but I believe there was an SL logo on them.
I do have a rev limiter (Crane Hi-S ignition) but I've never totally trusted it. I try not to take the engine above 6000rpm (also where rev limiter is set). I have my shift light set at 5800rpm.
Here's a link to my website where there are some other specs listed: engine specs
Thanks.

 

I feel your pain. Sorry to hear this.

I agree with The Dude. Try and measure the top ring end gap in the cylinder and see what the clearance is.