Hi , i was driving my 73 914 with a 1.7l engine and suddenly a knocking sound appeard and the sound will change depending on the revolution of the engine, i drove back the car to my home and it does not seem to have change nothing to the performance of the car but the sound sounds like the engine knocks .

any ideal what it could be ?

regards

Heck of a first post. Sorry to hear it.

How is / was / your oil level? Drain what is in there into a clean oil pan and see if you see shiney flecks in your oil. If so, its time to rebuild your engine, as those flecks are bearing material. Don't drive on it any more, you do not want it to seize on you.

and good luck!
Zach

Ok, a couple of questions, although I think that Zach may have hit on the final answer without them;
1. Does the knock (deep knock) happen more when the engine decelerates? (likely rod bearing)

2. Is the knock a fast knock or about 1/4 the frequency of the engine rotation? If it is a fast knock it is likely crank related, if slow, valve train.

3. I agree to pull the oil AND the screen, then cut open the filter to see what particles you are seeing. If you don't see much, take a good look at the rocker arms and see if any have had a significant change in tolerance.

4. Did you check the exhaust system lately? Sometimes people can confuse an exhaust leak with a knock, sorry if this is insulting, just trying to cover all bases.

This is a great place to hang out and get help with your 914. No matter what it is, it is likely someone here has done it or had it before...

Good luck and if you can grab some video or sound recording of the engine, that might help too, but be prepared to tear it apart to find out what the real issue is.

tanks guy's for helping me , here is a link to a video i just took to help you understand the problem .

http://www.youtube.com/watch?v=WY-X4vhEFOk


p.s. it seems the noise was louder when the engine was hotter.

When was the last time you adjusted the valves. Start there. This is KISS principle. Keep it simple first.

i dont know when it was done for the last time, i bought the car 2 month's ago.

Echo

That sucks.
If you don't have the coin for a full rebuild www.mikes914s.com/ might have a line on a 1.7

He's in Coborne ON about 2-1/2 hours east of Montreal just off the 401.

what would a full rebuilt go for ?

Was it suddenly a loud boom-boom-boom-boom?
Check for a spark plug that popped out.

Lighter banging, dropped seat, do a valve adjustment look and for an overly tight or loose valve.

A rod bearing will get louder. Not as loud coasting, but accelerating and gearing down quite loud.
By the time you got home was it louder than when it started?

Full rebuild is not cheap, I used to do them but a bunch of parts are more expensive now and good head cores are getting almost none existent.

by the time i came home it was lighter. today added oil 9 there was still oil in the engine ) and i started the engine and the same sound as when i took the video . but after reving the car a little all of a sudden a louder sound appeard like yesterday like somthing came loose . whit a bigger knock .

Stop running that engine man ! ...

...

I hope its a valve seat or loose spark plug...
but it sounds like my motor when I broke the crank in 2...

your going to need to check the valves, run a compression check, check the oil, and check the fan (that nothing got in there)...

then likely pull the motor and start disassembly until you find the culprit.
pull the heads from the motor first... but I'm guessing broken crank and that means a full disassebly and new motor.

you may want to just find/buy a new motor after the pulling a head step, and then disasseble at a more causual pace

You say there's no affect to performance?..... Sounds like the exhaust is blowing at the head..

Pleas stop running the engine until you have an idea of what is broke.