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1999blacka4
04-18-2013, 11:42 AM
Hey everyone,

My buddy says he bent a push rod in his 2001 audi a4 1.8TQM. I didn't think this engine used push rods. Do they use them and how hard are they to replace? Thanks

Fourplay
04-18-2013, 11:46 AM
No push rods in an OHC engine, so no.

redline380
04-18-2013, 11:51 AM
ha i just got a good laugh. no, audi's do not use ancient engine technology to open valves. if he bent anything, it could be valve. but we would have to hear symptoms to determine the proper diagnosis

Artiemas
04-18-2013, 12:54 PM
Who uses pushrods anymore?

98A4TurboAWD
04-18-2013, 12:57 PM
ha i just got a good laugh. no, audi's do not use ancient engine technology to open valves. if he bent anything, it could be valve. but we would have to hear symptoms to determine the proper diagnosis

lol yeah man like those ancient LS9 motors in corvettes that are doing over 200 mph while still getting 16/26 MPG.

Yeah these Audi's are so superior with their superior gas mileage in their 4 bangers and it isn't like they all bend valves at one point or another. It's that modern superior audi technology.

Fourplay
04-18-2013, 01:11 PM
lol yeah man like those ancient LS9 motors in corvettes that are doing over 200 mph while still getting 16/26 MPG.

Yeah these Audi's are so superior with their superior gas mileage in their 4 bangers and it isn't like they all bend valves at one point or another. It's that modern superior audi technology.

Just because GM clings to outdated technology and has spent 60+ years perfecting it doesn't mean it's a good design. A bad design executed to perfection is still a bad design.

98A4TurboAWD
04-18-2013, 01:27 PM
Just because GM clings to outdated technology and has spent 60+ years perfecting it doesn't mean it's a good design. A bad design executed to perfection is still a bad design.

lmao!! I wouldn't cling too hard to that opinion. At least don't say it in public. Maintain the anonymity of the net.

zandrew
04-18-2013, 01:45 PM
lmao!! I wouldn't cling too hard to that opinion. At least don't say it in public. Maintain the anonymity of the net.

I wonder why modern push rod engines use spring rates in 300+ psi range yet can't spin past 6k and an ohc uses 80psi springs and can spin to 8k with no valve float. hmmm has something to do with frictional loss. I'd look into that and also look at hp per liter. Then get back to us about how great push rod engines are(not)....

they get the job done but in no way are they super efficient when compared to the efficiency of a good dohc

gm has not went to dohc for other reasons. one is that they have a ton of money tied up in the research of this push rod and since it fits its application why change ( or spend money) to make it ohc. imagine the greatness it could be if they did change to ohc....

redline380
04-18-2013, 03:34 PM
lol yeah man like those ancient LS9 motors in corvettes that are doing over 200 mph while still getting 16/26 MPG.

Yeah these Audi's are so superior with their superior gas mileage in their 4 bangers and it isn't like they all bend valves at one point or another. It's that modern superior audi technology.

i knew someone was going to blast me for that. i said it was ancient technology. i didnt say it was ineffective or a poor design. its still around for a reason. note the truck i drive<<<<<

Nollywood
04-18-2013, 03:50 PM
Who uses pushrods anymore?

LS series V8's. And they're pretty robust too.

terraflata
04-18-2013, 04:36 PM
Develop an F1 car that uses pushrod technology (and no, not suspension) and remains competitive and Ill give in. ZR1 is still a beast, but I definitely agree that OHC Technology is superior.

zandrew
04-18-2013, 05:04 PM
terraflata- Nascar motors are getting damn impressive but they are designed for 750 miles and that is it. If you compare this statistic to the fact that F1 motors that rev even further and are designed to last several races the DOHC setup then proves its worth. Too give you an idea the F1 motors use pneumatic valve springs with a psi range around 100-150psi and rev to 18k without float. Nascar uses mechanical valve springs with 600-700psi and can "only" get too 10K without valve float. There are a lot of other trick parts inside these motors but these are specific features to each design. With the V8 you need so much spring pressure to accomadate the frictional loss and side forces exhibited by the cam, lifter, push rod, and rockers opposed to the bucket over valve (or lifter on valve) design.

Funny thing is in the late 60's ford came out with OHC designed 427 and Nascar would not allow them to compete with it. Ford went too the dragstrip with instead and ate the competetion up. It was specifically designed to compete with the 428 Hemi. They are extremely rare and extremely valuable motors now.

I guess in part GM owners has Nascar to thank for the aging push rod design. I am not saying they are not OK motors nor robust. Just saying that OHC is far superior.

spindoctor
04-18-2013, 06:54 PM
F1 engines vs NASCAR engines

Here's a good read

http://www.epi-eng.com/piston_engine_technology/comparison_of_cup_to_f1.htm

M-Hood
04-19-2013, 09:09 AM
Hey everyone,

My buddy says he bent a push rod in his 2001 audi a4 1.8TQM. I didn't think this engine used push rods. Do they use them and how hard are they to replace? Thanks

Easy to replace, just tell him to get a new valve. lol

1999blacka4
04-19-2013, 02:42 PM
Not sure his symptoms exactly. I kind of think the T belt snapped but he said whatever it was it caused the engine to blow. He has 7,000 invested and I am buying it off him for $400 to fix or use for parts. Its in mint condition disregarding the engine. [wrench] [a4]

sweets4style
04-19-2013, 03:48 PM
GM's LS motor has a better CG of any motor out there that I am aware of. Their weight is centered substantially lower then just about any OHC motor. They are shorter as well then most inline and V 4 cylinder engines making them more compact and more easily located further back in the chassis. From an engineering standpoint thats quite a win that many cant compete with. And very soon you will see direct injected push rod v8s.

Friction has very little to do with the reving ability of the motor. And if your going to state they make more friction, which I dont even think you know is a fact, then you should also state they use 1 cam instead of two or even 4 to drive two banks, therefore somewhat cutting friction from a cam journal perspective. The rest of the extra components meaning push rods and rockers have tiny contact areas and many new rockers are roller bearing style for virtual friction free design (virtual not really friction free). The reason why f1 engines can rev out further is because they run small displacement engines. What I mean by that is they run multiple bores to increase piston but keep weight down from the piston/rod combos. Reciprocating weight is kept down creating non terminal piston speeds. Thats the only thing keeping the very large bore american push rod engines from higher RPM use plus sometimes the rod/stroke ratios at the extreme side of the displacement you can get from some of them. If you built a comparatively smaller displacement push rod engine you wouldnt see that limitation on RPM that you do with current large displacement v8s. Its just simple physics. Spring pressure prevents valve float at high rpm's and like someone said there are even pneumatic options. But dont buy for a second it has anything to do with frictional losses that pushrod motors are limited. In fact they arent limited by that at all.

I am not even an expert on push rod v8s and I cant tell you that with almost 100 percent certainty. And spring pressure of the valve spring isnt a virtue of just stating pressures. They are relative to valve size and number of valves in teh chamber. So its not an apples to apples comparision.

1999blacka4
04-19-2013, 03:56 PM
Sorry guys, didn't really mean to cause an argument. Everybody Love Everybody (ELE)

contrldsub
04-19-2013, 04:16 PM
the new chevy ecotec motor is DoHC, direct injected and turbo charged.... if im not mistaken, GM produced the Northstar motor in alots of models in a V6 and V8 design. and that was DoHC motor that could be found in chevy's, olds, pontiacs.. still being used in todays models too. My 2001 Yamaha R1 is 998cc, and from the factory 152hp. do i agree that DoHC is the better tech, but it isnt what everyone wants. do it yourselfers like simple engine designs which is why many of the trucks still use pushrod Cam in Block motors.

terraflata
04-21-2013, 09:06 AM
Arguements are great for discussions, ELE lol. I always thought F1 engine could rev so high because of the extremely short stroke, meaning that at 19k RPM mean piston speed could be lower than another engine reving at 7k. The short stroke means no torque, but since an F1 car doesnt weigh much, doesn't suffer.