knock knock knock pistons???

T

Thor

Member
hello!

i have fit Mahle 86.44 mm pistons with 9:1 compression. Now i have heard that the engine knocks if i start up. Is it possible that the pistons makes noise when it is cold?? The pistons was fit in these block 10 years ago but the engine never was finish. I had bought them and put it into my car. Now the engine has 1500km done!

I am happy if you could help me!

cheers
Sascha
 
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pulsarboby

Guest
yes the mahle pistons along with je and weisco sare noisy on start up untill engines at full running temp so nothing to worry about
 
T

Thor

Member
that´s sounds nice bob! but is it possible that the noise i had heard first time after approx 1200 km? what i have seen too is, that the afr after accelerator is very rich and few sec later all is ok. may be the Z32 maf makes these prob or the pistons?
 
A

Animaldaz

Active Member
Ive just replaced my cams (oe cams etc) and they were alot more worn then that, particulary the peaks of the lobes. They had a very prominent ridge where it runs on the rocker and they were also deeply pitted but they were not noisy.
 
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pulsarboby

Guest
it looks as though the cams have been running dry so yes they could make a knocking noise if so!
think you span a shell recently....are you sure the oil spray bar is clear and oil pickup to the head is good?
 
splmum

splmum

Active Member
I'm not a mechanical engineer, but I would have to say that those cam's are just about knackered.

If I had cam's in my R that looked like that they would be getting chucked into the scrap bin.

All those pieces of metal ground off there are now, or have been, floating around in the blood (oil) of the engine causing it too have a stroke waiting for the heart attack to occur.

jmo.
 
T

Thor

Member
Now i had get heard with a screw driver the knocking noise on the head 3rd and 4th cylinder. The block don´t make noises.

Than had take a look on the oil pipe for the cams and they was blocked with seal paste! I had cleaned them and now the drop oil on all holes.

But which make the noise?
 
T

Thor

Member
Now i have checked the compression and alle cylinders had approx 11.5 bar. Than i have changed the tensioner and some shims from the valve train. The knocking sound i hear is much lower. But not gone!

BUT what is it if the engine knocks (read the power fc approx 50 level) when the engine is cold? If the engine is warm all is ok. Any idea???
 
T

Thor

Member
after 1500km at the new engine? so i have everytime warm up before i pushed the car and never more than 1.4 bar of boost....
 
red reading

red reading

Active Member
Forged piston's expand more than cast (depending on the alloy used to make them) therefore they need larger bore to piston clearence,hence when cold you get piston slap, i.e knocking when cold
 
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pulsarboby

Guest
and thats also why you cannot use any piston lets say in an 87mm bore.....each individual make has a different piston to cylinder clearance.
in other words a set of weisco 87mm pistons fitted cylinders bored to spec of lets say a cp 87mm you will find the weiscos are a tight (too tight) fit.
thats another reason why its very important to gap the rings correctly
 
T

Thor

Member
i think the bore clearance is correctly at the cylinders. i just wonder about that why the first 1500 km all was ok and runs beautiful. the knock i heard was louder from day to day but the noise comes 100% between the headgasket and camshafts! NOT from the block!!!
 
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