Knock knock!!! Something in my 85 SVO wants out!!

[pstocker]

I wish I could accurately describe the noise my engine is making, but from what I can tell, it sounds like a rod knock. It is not there in the morning when I start my car, but not too long after she warms up, you starts knocking, most noticeable when under mild acceleration. It sound like a hollow knock, not like a ticking noise. Can a lifter make a knock instead of a tick? I have isolated it back to number one cylinder by unplugging the plug wires one at a time and revving the engine. When I unplug number one, it stops. It make no noise at idle and overall, it runs very well. My oil pressure, if you trust the factory gauge, before the engine warms up, is around the 'M' to 'A' on the gauge. After warm up, and at idle, it can go as low as just below the 'O' in normal.



Any idea which way I should go next?

[Alex L]

I have isolated it back to number one cylinder by unplugging the plug wires one at a time and revving the engine. When I unplug number one, it stops.

oh boy, you're just not having any luck lately are you? think it must be something in the ohio river. if the noise stops after you remove a plug wire, that points at something in the bottom end. stop driving it immediately till this is repaired, otherwise you may do more damage.

does it knock at idle, or only above 1800 rpm?

[Laredo]

....Any idea which way I should go next?

Park it until you figure out what's broken.

Based on what you're describing, you need to start pulling bearing caps off the crank for inspection. Better figure on pulling the motor - this ain't good...

[Alex L]

... *sigh* please ignore my pre-coffee name mixup between dpmeeks/pstocker and the ohio river reference. x2 on the bearing caps and pull the motor.

[bob tweedy]

knock

it might be a cracked piston. i dont like the below o oil pressure.
bob

[pstocker]

You cannot hear it at idle, but when the car is really warmed up and sitting in traffic or something, the oil pressure gets down onto the N in NORMAL. Again, this is the factory gauge, so however reliable that is right?

So stop driving it seems to be the consensus? Ok, will do. Time to pull a motor!! Good thing I have my own engine hoist!! :-) I do have a spare 88 TC long block. Maybe I should just use that for a rebuild. This really sucks because I finally get my LA3 in there and she is running SOOOOO good, and this crap happens. Arggg....

[Alex L]

if the TC longblock is usable, just slam that sucker in while you triage the longblock that's in there now.

[pstocker]

if the TC longblock is usable, just slam that sucker in while you triage the longblock that's in there now.

Well, that would work, but the TC engine needs rebuilding. I got it for free, but the bonehead that I got it from left it sitting outside, uncovered and open to the environment for about 2 years. But, it's free right? So, needless to say, it needs work.

I am pretty sure it will need to be bored out due to the amount of rust in the tops of the cylinders. Who makes an economical forged piston in an oversize that I can use in the TC block?

[gbeaird]

Opportunity to freshen things up, and clean up the engine bay. Not sure what I'd do other then just clean and R&R bearings/rings and such. The stock block is pretty robust.

[pstocker]

If it does end up being a bad rod or main bearing, and if there is no scoring on the crank, is it possible I could just get away with changing out the main and rod bearings?

Thanks for all your input. -Phil

[Alex L]

Yup. One of those $5 part, 15 hours labour deals

[pstocker]

Yup. One of those $5 part, 15 hours labour deals

How can you tell the difference between say a rod knock or piston slap? Would piston slap get quieter as an engine warms up and the opposite for rod / main knocks? I know either way it has to come apart...

[Alex L]

never had to deal with piston slap, so i dont know first hand, but my understanding is piston slap quiets down as the engine warms, and rod bearings get louder as rpm increases, and will knock at a lower rpm as the oil warms.

[pstocker]

never had to deal with piston slap, so i dont know first hand, but my understanding is piston slap quiets down as the engine warms, and rod bearings get louder as rpm increases, and will knock at a lower rpm as the oil warms.

Thanks Alex!

[pstocker]

Well, spent all day Saturday in 101 degree weather pulling the engine (by myself) from my 85. This coming weekend, after I recover from last weekend, I will be dropping the oil pan and checking the bearings (clearances and such) and probably replacing them all. I also found a reason for another weird noise my car was making. The clutch disk and the pressure plate were FRIED!! Not my doing of course! I mean, the pressure plate looked like brakes when they go metal to metal. Good thing I have another clutch ready to go it!! The disk was so bad that the you could shake it and hear the springs rattle!! :-) Fun Fun!! I might pull the head, even though I did not have any compression issues, just to check the pistons. Not sure about that yet!

Oh, and I also found that my transmission mount had completely separated!! Could this cause my driveline vibration that I was getting at 65mph up? (very bad vibration).

Thanks

Phil