Maintaining a DOHC

[Sidewinder]

I was just curious how difficult the DOHC engine is to maintain versus other GM V6 engines. I ask this because I am in College, and maintaining the engine on a regular basis may be difficult if things constantly go. From what I understand, either people say that the engine is great or the engine isn't good at all (a mechanic told me that as well). I just wanted some more opinions on the engine before I start going nutz and putting it in my car.

At the same time though, since I am working on an engine rebuild for this engine, I'll probably know it really well and should be easier to work on. Anyway, what do you guys think? Whats required for regular maintenance thats different from other engines?

[PCGUY112887]

Everytime I talk to a mechanic about my GP, they are like 3.4

Hah I have never had a 3.4 nor have I ever worked on one, but if you are rebuilding it then it should be fairly strong and not have many issues.

[93Oldsdroptop]

The 3.4 is just another engine. Some things (timing belt, alternator, leaky 'o' ring seal) are a bitch to work on. Same as any other engine. Seems to me that the key thing with these engines is maintenance. If you get one that's been taken care of throughout it's life, it will probably run forever. But if you get one that was not taken care of it won't last.

[mashing-the-accelerator]

I was just curious how difficult the DOHC engine is to maintain versus other GM V6 engines. I ask this because I am in College, and maintaining the engine on a regular basis may be difficult if things constantly go. From what I understand, either people say that the engine is great or the engine isn't good at all (a mechanic told me that as well). I just wanted some more opinions on the engine before I start going nutz and putting it in my car.

At the same time though, since I am working on an engine rebuild for this engine, I'll probably know it really well and should be easier to work on. Anyway, what do you guys think? Whats required for regular maintenance thats different from other engines?

I got my DOHC 5 years ago, put lifetime plugs in it, changed oil to synthetic, replaced one coil pack, and proceeded to put 50K on it. Never missed a beat.

IMHO, it's no different than maintenance on any other engine- I run synthetic oil in the engine/trans to extend drain intervals, also run a good lifetime spark plug so you aren't changing those every year or two. (I run the Bosch 4-prong platinum plugs) The original belt in mine ran over 150,000 miles before I changed it, and it still hadn't broken yet at that point. I put over 50K on my car, and bought it with 100K on the clock, it still runs like a bear and looks great. The main thing is, find a good garage that can diagnose the ECM/sensor problems if/when they crop up. After you put the engine in, do a fuel pressure and exhaust backpressure test. Some bitch the timing belt setup, but even steel timing chains in other cars stretch and jump time eventually anyway, so IMO that's a non-issue. I've seen steel double roller timing chains with tensioners eventually stretch to the point they are out of time and won't start, on the old Datsun 240Z cars. How bad can the timing belt be ? All the NASCAR guys use timing belts now, for that matter. The only engine I can see better than the DOHC V-6 would be the 3.8 pushrod V-6, simply because it's bigger by .4 liter. (it would be nice to shoehorn the old 4.3 liter into a FWD, has anyone tried it ? it's a 305 SBC with 2 cylinders chopped off) But there's something about running 4 cams that is really cool- the DOHC runs like a jet with a wide torque band due to those cams in the head.

one thing about the DOHC, the aluminum heads move around on the block a little with time, and eventually may start leaking oil from the head gaskets/oil return passages, near the outboard edge of the block- the head bolts are "throw aways", i.e. if you change head gaskets, you have to get new head bolts too- they are "torque to yield". But this is not an issue with a rebuilt engine, it's something you may run into as an OEM engine approaches 200K miles on the clock.

[thestoned0ne]

one thing about the DOHC, the aluminum heads move around on the block with time, and eventually may start leaking oil from the head gaskets- the head bolts are "throw aways", i.e. if you change head gaskets, you have to get new head bolts too- they are "torque to yield". But this is not an issue with a rebuilt engine, it's something you may run into as an OEM engine approaches 200K miles on the clock.

Hmmm Good to know

[mashing-the-accelerator]

Hmmm Good to know

yep, that's right in the repair manual, and also in the computer at Advance Auto- under head gaskets, it says "bolts not included"- and on the same page, lists the head bolts

years ago we had a Ford 4-cyl w/aluminum head, that blew a head gasket- the manual said change head bolts with gasket, my boss thought it was BS- we tried to use the original head bolts, they simply would not torque, they kept turning and turning, not reaching the torque spec. We pulled it back apart, and the head bolts were stretched like spaghetti.

so we got new head bolts and they torqued

these new engines have shit for head bolts

[OldSkoolGP]

mashing, seriously. How dumb do you think we are?



Your inputs and opinions are not welcome here, that has been made perfectly clear. We can easily figure out your new screenames and ban them just as easily. Do us all a favor. Grow up, realize you screwed your own self over by being an asshole in the first place, and move on.

[bszopi]

This latest is hilarious... You obviously don't think things through. You have your age listed as 19, yet you put in plugs 5 years ago and have driven 50k on them.

Guess we'll just have to start restricting new users.

[Sidewinder]

Apparently I missed something lol

[3100 MPFI]

Don't worry about what you are missing Sidewinder. Not worth the stress.

As for the plugs, I do NOT recommend using ANY bosch plugs. I have had too many issues with them. They do not hold up, and burn out way too fast. They can't handle the power of the GM waste spark DIS.

Best plugs that I have used are GM RAPIDFIRES. They cost a little less than the bosch 4's and they last a lot longer. I put the bosch 4's in my high compression 3100, and it blew the core out in less than 2000 miles. I put some rapidfires in, and they were still good when I changed them out 6 months ago (almost 4 years old). I just changed them out because I broke on. Forgot to use antiseize.

[dohcfiend]

this engine to me is actually one of the easier engine to work on. like anything else it gets easier with experience.

if you are doing a rebuild, you shouldn't have to worry much about maintainence for a while.

with the exception of the timing belt(which i think calls for 66k) most of the parts failures are occurring on high mileage engines where they are way past of spec to begin with. the belts i think are well built as long as they are installed properly they last not only up to spec but usually exceed spec by a decent margin from observation.

if installed properly, only things i have noticed to fail prematurely are the alternator with the automatic tranny and the coilpacks on the 91-95 engines.

the coilpacks can be remedied by relocating them away from the exhaust manifold. most choose the 96 location and switch to 96-97 valve covers to use 96-97 plug wires but you can put them where ever you like but some planning may be in order to get your stock wires to work or buy and custom cut wires.

the alt sometimes fail prematurely due to poor manufacturing standards of some of the parts store sources. other than that they fail due to poor installation by not properly installing that heat duct and they fail due to heat absorbtion even with a proper install. i always say get it done LOCAL. when your alt fails most local shops will charge the same as a new alt from a "large discount retailer". so you're going to spend about the same amount either way. not only that you will support your local small business economy and IMO they are (re)built better than by a 10 year old in some 3rd world country.

only thing i can think of that MIGHT prolong the life of the alt would be to possibly wrap half of your downpipe in some header wrap. on the 5 spd cars there is more adequate ventilation and less failures IMO.

p.s. replacing the alt is a huge PITA.

my .02

[pwmin]

i agree that a lot of things on these engines are easier than their pushrod counterparts.

i get paladium alternators from advance. iirc, they are actually delco rebuilds. i bought a 160A? from mr. alternator, and it went out pretty quickly.

[RedZMonte]

T-belts must be done. Alternators go out and are a BITCH to replace. I have blown both my stock alts. when i put my sterio in. once i replace the alt with a new Delco i have never had a problem (this is true on both my dohc's). Oil Leaks (dist. O-Ring, Intake valley Gasket). Intake Gaskets going bad give a bad idle when cold. Rubber Brake Booster Hose turns to mush and needs replaced. Trans Service is a must!

thoes are the problems i have had and i know are common. I have had other problems like Broken Diff. But i can take the blame for that one..... Trubo, 6500RPM on ice then finding pavement.

[bve32k]

I hear a IP ban coming up!

Now you are 20!

[SappySE107]

Gone again, along with his incorrect information.