What the F£CK!!!!

[Mark Halligan]

You say it sounds like slap, does it go when warm?
Jay

Yep it goes away once the engine is at operating temperature, I wouldn't say that it breathes particularly heavy and the last comp check I did came up fine. When hot the motor sounds and goes well.

[Mark Halligan]

Bottom line is if it is just slap observed at cold temperatures then its no big drama, BUT it sure would be nice to know the clearances and piston ring gaps on yours and Doug's to see if there is any difference.

Paul

As I posted further up the page, I have measured the clearances when I took it apart a few weeks ago

Using a digital micrometer I did measure the bores when I had it out and I got a bore figure of 81.48mm and a piston at 81.35mm, giving a clearance of 0.13mm. Whilst I am not the greatest at using a micrometer, I believe these are fairly accurate readings.

Obviously I dont know what clearances Dougs running.

[Doug_RS2]

Obviously I dont know what clearances Dougs running.

And neither do I - the shop followed the JE instructions on the bore sizing - or, I hope they did.

[Pisobiker]

JE instructions say, for pistons whitin 3.625" bore:

min piston to wall clearance .0030" to .0036"

then they add these are MINIMUM clearances for the 2618 aluminum alloy pistons, while in some forced induction and nitrous applications clearances might need to be increased of another .001" to .003"

So even taking the smallest of the two it makes .0040" (0.1016 mm) for a high perf. turbocharged engine.
I did 0.100 mm on mine, hopefully it will work fine (will see soon), but it still is a big piston to wall clearance compared to std OEM pistons (0.03-0.04 mm), which I guess might cause same noise during engine warm up.

Maybe Mark's machineshop stayed in the middle of what JE suggested (.0033"+.0015"=.0048" or 0.122 mm) while Dougs machine shop did only the .0030"..... ?


Just some thoughts


Marco

[Thuppu]

What do you think, can I use pistons like this still? No defects on the sides and piston ring groove.

[driftin jo]

What do you think, can I use pistons like this still? No defects on the sides and piston ring groove.

You could use them but you might want to smooth out those dents a bit so there are no sharp pointy bits that could cause hot spotting and thus detonation .

[Thuppu]

Ok, great. That was just what I was thinkin.

[benntenn67]

Knocking

Hello,
Here's my contribution. I agree it is important to be precise about the cause. Not intended to be definitive.

Pinking-Light metallic clinking sound.
Cause-Ignition too far advanced.
Mechanical rattle nothing to do with combustion.

Knock-Knocking sound caused by the collision of two flame fronts.
Cause-Mixture ratio, ignition timing, comp ratio, spark plug position, combustion chamber shape and fuels ability to resist knock.

Pre-ignition(AKA Denotation)-Fuel and air burn before spark arrives.
Cause-Something in the combustion chamber getting hot.
Usually spark plugs(wrong grade)are the source of problem although weak mixture or advanced timing contribute to the cause.
Severe engine damage.

Out of interest, what plugs are people running on their modified engines.

.... years ago, you could hear loads of cars driving around "pinking" especially the Ford cortina, capri etc - petrol was sold as 2,3 & 4 star - 2* being the cheapest, was often put into the tanks of cars designed to use 4* memories memories