Piston Slap | How To Mitigate It And Why It Occurs [HPA Q&A]
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- čas přidán 11. 05. 2019
- How do I mitigate piston slap? Why does it happen?
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Had a block bored out and fitted to 3.5 thousandths clearance per CP pistons specs. The resulting slap ended up polishing the cylinder walls on both thrust surfaces from the pistons rocking in the bores. There was a polished spot on both the top and bottom of the skirt from changeover. These were un-coated pistons. I ended up re-honing (yes the bores opened up to about to 4-4.5 thou) but I sent the pistons out to be coated to take that space back up. They actually came back wider than the bore. I then sanded them down until they fit snug. The engine has been run back in and burns 0 oil. Spark plugs look pristine. I have no idea how long this coating will last (it has been a few hundred miles), but, I learned my lesson. Pay the extra for the coating. It seems to really help alleviate minor thrust issues. These coatings designed to be set up tight and "wear-in" are definitely the way to go. Let the piston self-clearance. you'll get the perfect load distribution across the skirt as high spots wear in.
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great stuff! I've learned that sometimes, the block design itself calls for a different tolerance than what even the pistons manufacturer says. my last build has pistons to wall clearance of 3 thou. Once taken apart, the wall has wear marks. This time around I set it at 4.5 thou. the piston moves a little more in the bore but I think it'll be alright.
I think it's one of those experience things. The more you build engines the better you get at it.
can replacing a piston stop piston slap?
if you rebore the cylinder bore do you need a larger than specification piston to avoid piston slap?
thanks.
Hey great job as usual..
Can you give a lesson on e85
Cheers Ricky! We actually have an entire course on E85 tuning. Here is one example from it: czcams.com/video/m-Sj8WkWH6E/video.html - Taz.
Ok..... here is the best advice ever on piston slap..... I rebuilt my vq40 engine ..Nissan navara d40.. forged JE pistons from flatlander racing!!!!the only problem I had is the machining of the block... I.e to big!!!! ..........2 cylinders were 1 thou bigger than the others!!!! Result...... noisy cold start....and even a little noise when at temp!!! Fix...... change to valvoline xld 10w-40... ... this is a full mineral oil that costs at least half of full synthetic!! Please let everyone know that full mineral oil has a very good dampening effect on piston slap!! .... please try it!!!! It's not a joke!!!.... and this is like for like... as in 10w 40 to 10w 40...... TRY IT BEFORE HAVING A SHOT AT IT!!!!!
A
Yh but running mineral oils for a long time wont be healthy for your engine.. thats why people generally use fully synthetic
I want to try it but anything but full synthetic on a wrx sti is bad.. I do use 10w40 fully synthetic though. I hear it a bit when driving after starting for 10 minutes or so, but it goes away and I only hear it between 70-77km
Jack Gibb running mineral oils aren't as good as synthetic but you can still run an engine 500 thousand miles on mineral oil. Regular oil changes are the key!
l y m a x you don't have to try it!!!! If the noise goes away after the engine is hot.....It's all good!!!! It's just very annoying to listen to for the first 10 minutes!!! I wouldn't be to worried at all!!! It will still bug you though!!!
Pretty useless without examples of what piston slap sounds like
Then learn to google the sounds of it first and not be a useless twit yourself. Lazy fucker
@@rylandorr I googled for days and couldn't find an example were the creators of the videos didn't even know what they were dealing with.
Roger Retired hands on professional engineer (experience steam engines railways, all harbour equipment, jet engines altitude test facilities, air ground comms, cars and all personal and household machines answers. Wife has a Hyundai i30 which suffers with “slap”. Reason the piston skirt is too short. So there is insufficient side area to cushion the side thrust from the gudgeon pin and the pistons wobble in the bore. We use upper cylinder lubricant dosing of the fuel containing the dry lubricant molybdenum di sulphide. This reduces the slap to an acceptable level for someone who feels for mechanical equipment. Two to three teaspoons full per tank of fuel.