how to detect bent rod?

silvermiata · Postby **silvermiata** » Thu Apr 10, 2008 11:54 am

when its idling (900 rpm) my car shakes slightly... i was wondering why this could be... idle looks very steady on 900rpm. i was wondering if it would be a bent rod.. is there any way to detect it without taking the engine apart? my car is nb8a with around 100 000 k's on it...

sabretooth · Postby **sabretooth** » Thu Apr 10, 2008 12:24 pm

You'd have noticed some serious engine issues if a rod was bent.

It could be a dodgy engine mount, a dirty plug, a dying plug lead. I daresay it's a simple problem.

manga_blue · Postby **manga_blue** » Thu Apr 10, 2008 2:28 pm

x 2 I'd definitely look for a simple ignition or injector problem before thinking the worst. Try removing one plug lead at a time while idling. If removing one particular lead has less impact than the others then you know where to start. Then isolate it to ignition or injectors by swapping plugs and/or plug leads (2/3 interchange, 1/4 interchange on an NA).

silvermiata · Postby **silvermiata** » Thu Apr 10, 2008 2:45 pm

thanks for the info guys.. i have changed my leads about 6 months ago and i am running iridium plugs... could egr valve be the problem? but the rpm is steady? anyways i will take the egr valve out and give it a good clean then see if it makes any difference...

sabretooth · Postby **sabretooth** » Thu Apr 10, 2008 2:53 pm

In your case I'd be checking that the engine mounts are OK and that the relevant bolts are done up tightly.

Garry · Postby **Garry** » Thu Apr 10, 2008 2:59 pm

My car has a very slight miss at idle, it always has from day one. Over my time with the car plugs/leads/filters/fuel pump/EGR valve/tune/engine mounts have all been changed and it still does it. It's just the nature of the beast. If you have a vented block then it's time to worry. Until then enjoy.

Or take it to Daniel at Mania. He can apparently tell a bent rod by listening to the idle.

Benny · Postby **Benny** » Fri Apr 11, 2008 4:43 pm

From my experience, having a slightly bent rod (and most bent roads are hard to see even when you take them out to inspect them) only shows up as a lack of performance, caused by the reduction in compression ratio on the affected cylinders.
A compression test should show it up.

If your rods are bent like a banana, the engine will be almost powerless.

Sean · Postby **Sean** » Sat Apr 12, 2008 8:06 pm

Benny wrote:From my experience, having a slightly bent rod (and most bent roads are hard to see even when you take them out to inspect them) only shows up as a lack of performance, caused by the reduction in compression ratio on the affected cylinders.
A compression test should show it up.

If your rods are bent like a banana, the engine will be almost powerless.

I have some good pictures somewhere of Banana'd and snapped Mazda rods :oops: