Just a guess but the 3.4DOHC engine has a high redline. At high RPM's the stress on moving parts in increased exponentially. For this reason, I like designing and building my engines so that all of the power is in by 6000 RPM. I believe that it's better to be safe than sorry.
like dennis says,,i am guessing that gm made the engine till a point if u go beyond it u will pay..now if u want a stock engine fine dont push by reving the crap out of it,,now if u want hi-pro then build it for it,,dont be cheap it will come and bite u in the butt,,what i want to do is get the best bolts and maybe a gridle for the bottom end so does not move,,get a good set of steel rods with the bolts to match,,,get every thing machined and balanced will also make it better to rev..spend some now or spend alot more later..
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06:15 PM
sspeedstreet Member
Posts: 2306 From: Santa Maria, CA Registered: Dec 2002
What you are saying makes sense. Does anyone know if it's the bolts that are letting go? Seems like some ARPs would be cheap insurance. I chose the DOHC because I want to use the rpm capability of the engine.
Neil
------------------ 1988 GT, 5-speed, white, beechwood leather, trying to get a 3.4 DOHC put together.
[This message has been edited by sspeedstreet (edited 07-19-2003).]
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06:59 PM
Erik Member
Posts: 5628 From: Des Moines, Iowa Registered: Jul 2002
It could be many things but most likely are high miles, lack of maintenence and or bad knock sensors. The duty cyle of rods and bolts can be shortened dramatically with any number of over stressing such as pinging, overreving, diry oil etc. The TDC is a high revving sensitive motor and it likes its oil clean, a moment of oil starvation can kill it with spun bearings and thrown rods,the latter especially at high rev
Seems like I see a lot of 3.4 DOHC engines with thrown rods. Is this a rod bolt problem or an inherent design problem with the rods?
Neil
Really? I've only heard of cracked heads on the seams but never throwing rods. Wiping out the occassion rod bearing, but not breaking them. Any 60 degree engine for that matter.
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11:05 PM
Jul 19th, 2003
DKOV Member
Posts: 1564 From: Portland, OR, USA Registered: Mar 2001
In tearing up these motors the ONLY thing I've ever seen is spun rod bearings... never seen a Blown head or rod.
I guess it's an East Coast thing... humidity maybe?
DKOV -
DKOV, I've seen a few here in the midwest but the cars had high miles on them and the people who owned them werent the type that would take care of the motor. They even told me not long before it happened the SES light would come on. Also they were manual trans cars LOL. I bought one of the blown motors for parts. A rod had went through the side of the block. I did check out the knock sensors on both of them and they tested bad so thats why I would always check codes if they popped up. I just wanted to note that the rod wasnt broken just bent. The bolts are what goes on them. I would put some better aftermarket bolts on the rods if I rebuilt the motor.
[This message has been edited by Erik (edited 07-21-2003).]
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12:12 PM
sspeedstreet Member
Posts: 2306 From: Santa Maria, CA Registered: Dec 2002
quote Originally posted by sspeedstreet: Seems like I see a lot of 3.4 DOHC engines with thrown rods. Is this a rod bolt problem or an inherent design problem with the rods?
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By a lot I mean while searching carparts.com and other sites for a motor I will often see ones listed as "parts only" or "bad bottom end". I was just wondering if this was a trend or bad maintenance. Sounds like it must be the latter.
Neil
------------------ 1988 GT, 5-speed, white, beechwood leather, trying to get a 3.4 DOHC put together.
The DOHC I had in my cutlass lasted for almost 200,000 VERY HARD miles. I drive the piss out of that thing. To the point were I went through 5 4T60E trannys. They didnt fail do to neutral drops or rollbacks, just hard driving. I always changed my oil at 2500 miles AND I went 125,000 miles on 1 timing belt. Everyone says you can not get more than 60,000 miles on a timing belt with these motors but I proved them wrong.
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04:30 PM
PFF
System Bot
Jul 20th, 2003
GT Member
Posts: 911 From: Silver Spring, MD USA Registered: May 2003
From what I've read, they have a very long oiling system and a resulting low oil pressure. These things aren't neccesarily "bad" or "defects", but when someone who doesn't change their oil owns one of these engines, they are prone to bearing damage because of it. I'm curently rebuilding one that has a bad crank and bearings. The previous owner OBVIOUSLY rarely changed the oil.
-Rick Stewart
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11:17 PM
Jul 26th, 2003
fierosound Member
Posts: 15253 From: Calgary, Canada Registered: Nov 1999
The rods are the same as that used in 2.8/3.1/3.4 pushrod family. These are good to 7000 rpm, but with the DOHC, you are more likely to push the engine close to that rev limit.
------------------ 1987 GT www.fierosound.com 2002/2003 World of Wheels Winner & Multiple IASCA Stereo Award Winner
