Blown up motor
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Blown up motor

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    Default Blown up motor

    Alright guys i built a 30 over small block chevy motor stock rods, cast crank, flat top pistons it had one of those thumper cams in it from comp after about 100miles the guy calls me up and says it mad a ting sound a died i pull the valve covers of and one push rod is gone off the drivers side and passenger side and its locked up. I pulled the intake off and two lifters are gone also, pull the heads off and the cam has broke right in the middle and one piece of it got into the rod screwed it all up and the pistons is in pieces and the rod has knocked a hole throught the cylinder and into the water jacket. All the other cylinders look brand new im pritty sure the cam caused all this but summit and comp say its not there problem and only will warranty the cam what the hell is that good for when everything else is busted, and also busted the edelbrock heads that were on it. Comp cams arent worth a crap anymore are they and i did everything to break the cam in the right way it was a flat tappet

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    It was just a regular old 350 maybe 400 horse power, i have had comp cams in two of my boat motor that have lasted 10 years and are still going, but i guess you cant count on anyone making a good product anymore i think pro comp has taken over comp cams. You would think that they would have to fix everything that there junk product broke there is nothing there thats usable but the intake,carb, rocker arms. The piece of the cam thats rolled up in the rod it didnt go flat or anything its just broke. The comp guy says it must have got cracked when they shipped it. They want to send me a new cam but why would i want to put another one of those junk ass cams in a motor. I used the zink additive, broke it in at 2k rpm for 30 minuted like they said the head had single springs but new for the cam, the 7 other rod bearing look brand new it had 50 psi oil pressure until the ting. What do you think gn7 was it something i did or hell the comp cam guy already sid it wasnt anything i did they must have this alot

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    I think bullet makes a good product right

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    Quote Originally Posted by matt wheeler View Post
    the 7 other rod bearing look brand new it had 50 psi oil pressure until the ting.
    This part is a little concerning. What do you mean the other 7 bearings look brand new. Is this rod broken or just smacked by the cam or lifter piece. What does that bearing look like. You may have to post some pics.



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    Sounds more like the bottom end broke something and shrapnel broke the cam. There's guys here and there running way cheaper cams than that at higher HP levels.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    My guess with out seeing it is: tight piton pin, grabbed and tore the piston to hell. The rod no longer having the piston to guide it on the bore, was no longer indexed properly on the crank thru its rotation, and clipped the cam. the rod on a BBC doen't clear the cam by much to start with. The 3.75 crank won't even clear the cam with out modifying it. You take the piston off the rod and the big of the rod will hit the can for sure, becuase it is free to flop and put the rod bolt in a place it would not normally be if it was still attached to the piston.

    I'd like to know, other than some bent valves, why the heads are toast.



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    The combustion chamber took a beating from the piston pieces, the piece of the cam is still sitting in the spot it wedged the rod in about a 5 inch piece of the cam wedged in between the block and rod im real sure the cam broke and when the rod cam around there was the piece and pushed the rod and piston through the cylinder wall i will take pictures and show you what in tlking about. That piece of the cam is wedged were you cant get it out it so tight id the cam was broke when the something hit it it would have just fell and be laying there not wedged

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    Not necessarily. If the rod smacked the cam and broke it, its now free to go anywhere. No different than under your scenerio. With a crank spinning at even cruising speed, things happen in a blink. The rod/crank could hit a falling piece of cam 100 times before it could fall into the pan. Try to keep in mind, that a stock 350 rod, on a 350 crank, the THE ROD BOLT only clears the cam by less than .125, with the rod still attached to the piston and the proper side of the rod facing the cam at a precise angle. On a 400 crank, it doesn't clear at all. The same rod, on a crank with .270 more stroke, only .135 closer to the cam, and it will tear the cam to pieces. In fact, you can't even turn the motor over. So with a 350 rod, on a 350 crank, if you break a timing chain, the rod can hit the cam. If you break a piston, the rod can hit the cam.

    Not saying the cam couldn't possibly have broken. Just saying, there are way to many other things that could have happened to break the cam.



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    Last edited by gn7; 09-14-2010 at 07:44 AM.

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    Quote Originally Posted by gn7 View Post
    Not saying the cam couldn't possibly have broken. Just saying, there are way to many other things that could have happened to break the cam.
    Agree.

    I've never been a professional engine builder, but I have put several together. Until recently, I NEVER NOTICED how close the rods are to the cam! I had mentioned to my (now) builder that I wanted to know the main difference to putting my 350 back together as a 383 or leave it a 355. Mainly because we didn't know if the crank was gonna be useable or not. If not, I figured 383 cranks are just as much as a new 350 crank, so why not?

    Well, one of the things he mentioned is - clearancing the crank to the cam. Small base-circle and such. So, I became curious as to how close they are NORMALLY. Wow. I was nervous just watching a normal 350 assembly spin over.

    The motor we are talking about here, he says, is just a 350 - not a stroker. Unless there is excessive oil pressure or some form of distributor binding, cams SO RARELY break. Not that it CAN'T happen, but it rarely does.

    What, 90+% of the time a cam breaks it's because of a part that hits it? Gotta be somewhere around that %. If a set of rod bolts were not clearanced correctly or the angled head "twisted" a bit - throw some RPM in the mix, along with full temperature and parts could hit.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Quote Originally Posted by Beer:30 View Post
    Agree.



    The motor we are talking about here, he says, is just a 350 - not a stroker. Unless there is excessive oil pressure or some form of distributor binding, cams SO RARELY break. Not that it CAN'T happen, but it rarely does.

    What, 90+% of the time a cam breaks it's because of a part that hits it? Gotta be somewhere around that %. If a set of rod bolts were not clearanced correctly or the angled head "twisted" a bit - throw some RPM in the mix, along with full temperature and parts could hit.
    Your thinking to much that the cam could twist apart due to oil pump and dizzy. The oil pump and dizzy are nothing compared to spring pressure on the cam. Not just the downward force, but the also to twisting force as well. the biggest resistance to rotation in a cam is spring pressure. BY FAR.

    And although it would be very very difficult to have a rod bolt twist, or the head to be angled in correctly enough to hit the cam, it is entirely possible to have the whole rod out of wack due to a broken piston.

    If you assembled a motor, with one piston off, and rotated the motor over, I am pretty certain you could getthe rod to hit the cam. Simply by moving the small end back and forth, left to right, as you spun the motor. The big end of the rod on a sbc has to be in just the right place to clear the cam.

    If you think a SBC is tight, you should see a Ford 312 Y block. You break a t- chain, and a rod and the cam are going to meet.



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    Quote Originally Posted by gn7 View Post
    Your thinking to much that the cam could twist apart due to oil pump and dizzy. The oil pump and dizzy are nothing compared to spring pressure on the cam. Not just the downward force, but the also to twisting force as well. the biggest resistance to rotation in a cam is spring pressure. BY FAR.

    If you think a SBC is tight, you should see a Ford 312 Y block. You break a t- chain, and a rod and the cam are going to meet.
    True. I was more thinking of it as forces at opposite ends of each other trying to twist it apart.

    Could too big of a center cam bearing been put in? Not enough support in the middle of the shaft?

    I DO HAVE a Y-block. It's a 312 that's offset-ground to a 346. Custom ISKY cam, Chevy-size Manley rods, Chevy valves in the lightly ported heads. Single-4 barrel intake (Blue Thunder) with a 670 Holley made 323hp on the dyno. That's 100 or so above stock, so we were happy. I have NOT looked inside the motor, though. I will say again that we dyno'd it, so it's all broke-in and happy with it's clearances. Not meaning to hi-jack the thread.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Well all im saying is the rod didnt break its still on the crank its just bent were the piece of the cam is lodged in it and the wrist pin and end of the rod is stuck through the cylinder wall. I know what happend to the motor this is not my first motor to build i have built a bunch of motors im just telling you guys about how junky comps flat tappet cams are you guys can use them all you want but i will never use them again

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