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i have been knulling the pistons on all the engines i rebiuld to stop piston slap with 100% results the engines run dead silent and smoother i even do it when i rebiuld them it makes them verry tight takes longer to breakin but they last longer and dont slap ever agian think the knock senser likes it silent

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How much do you pay for that these days?

 

Last set I had done was a long time ago at NAPA for a six cylinder International. It didn't cost that much, and It's never crossed my mind for a Subaru.

 

Doug

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It could definitely work. Another solution to getting the skirt clearances up is to coat them with teflon, or whatever it is that SwainTech uses and is calling PC-9.... looks alot like a Teflon variant to me. :-p. The PC-9 is about $24 per piston plus shipping and can take up .004" of additional clearance. I have gone this route and have installed these in a 25D based frankenmotor (with careful fitment by adjusting the coating with 1200 git till the clearance was acceptable) and there wasn't any piston slap so I guess it worked :drunk:

 

Knurling could potentially take up a lot more than that. Easily in the neighborhood of .010" but I hope you wouldn't need that much on any Subaru engine.

 

This is more of a "trick" to avoid boreing oversized and buying new pistons. But it does work.

 

GD

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Replacing the pistons with the updated moly coated ones seems to work well too.

 

Yea, and new stock pistons aren't that expensive either.

 

Doug

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Yea, and new stock pistons aren't that expensive either.

 

A lot more expensive than coating or knurling. Hell if you coat the original pistons you have basically the same thing. Of course the turn-around time is longer to have them coated than to buy new ones. The coating can potentially take up more clearance also as the thicker coating is "adjustable" via polishing it down. Not so with the stock replacements.

 

GD

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i have customers that have over a 100000kms on theese engines and still no noise i find that coated pistons just loose the coatings and start slapen this method is cheap and seems to hold up for long time here in BC canada pistons are 300$ each as are parts suplyers realy suck so this is the only cost efetive way to fix problem

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have done 3 more all came in slapen and left dead silent i knurll 2@4 when i do the headgasket cost 150 $ extra but makes a hudge differnce that you can hear i think the piston slap efects timming so stop the slap engine runs way better still 100% happy with thiss repair cost efective and garentied fix

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any pics of pistons before and after?
+1 that would be sweet, i'm not familiar with knulling.

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Try searching Google for "knurl pistons", at least I think that's the technique being discussed here. It used to be done to valve guides too.

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the knurller holds the piston while a toothed wheel puts a cross hatch pattern on piston very simple machine i bought from a 80 year old machinist the knurler must be 60 years old works off air preshure the more preshure the deeper the knurl deeper the knurl tighter the piston to the point that a engine with all 4 knurled you can hardly turn engine i will post some pics of the knurler and some pistons. I even knurled my forged wisco pistons to get them a bitt tighter thiss is a proven fix have done many.

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I'm glad it works for you. But, if we tried a technique like that on any of our engines, our customers would refuse to do business with us, especially dealers.

 

If I understand, one advantage is to get more oil around the piston, but that can also result in blow by and smoking. I'd be nervous about the integrity of the piston itself also: Subaru pistons crack enough on their own with compromising the strength of the metal!

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I'm glad it works for you. But, if we tried a technique like that on any of our engines, our customers would refuse to do business with us, especially dealers.

 

Your business is supplying stock engines without thinking outside the box. That's fine. Ivan and people like myself supply what each individual wants and we are open to alternatives and improvements in design as well as custom builds. It's a fundamentally different kind of business. We do things you and the dealers will not do. Would you build a 2.5/2.2 hybrid for your customers? Or a 255/257 with 205/25D heads? I doubt it. Your business model is too rigid and inflexible to handle that much out of the box.

 

Anyway I highly doubt it would cause either an increase in oil consumption or any structural damage to the piston.

 

I for one plan to give this a try if I can find the equipment or a machinist that has it.

 

GD

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Actually, we have done some of those hybrid builds. Not too fond of them, but we have done them.

 

I'd like to think we aren't "rigid", but I suppose you're right: stock engines are what our customers are looking for when they come to us.

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I'd like to think we aren't "rigid", but I suppose you're right: stock engines are what our customers are looking for when they come to us.

 

If you wanted to get into other types of builds - just register a new business name and build them alongside what you build now. Of course - with something like that you would want to test out the engines and see what they can do, etc. A lot of businesses do that - Rockford constant velocity has RCV Performance - their "custom" division - for example.

 

What exactly are you not fond of about the frankenmotor build? It's cheap, reliable performance. I call that "fun". With a good used 2.5 block you can put one together for a few hundered $. It's a lot cheaper and more accesible than the turbo's and opens up the hobby to a lot of people that otherwise wouldn't be able to afford it.

 

GD

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I'm glad it works for you. But, if we tried a technique like that on any of our engines, our customers would refuse to do business with us, especially dealers.

 

If I understand, one advantage is to get more oil around the piston, but that can also result in blow by and smoking. I'd be nervous about the integrity of the piston itself also: Subaru pistons crack enough on their own with compromising the strength of the metal!

 

funny the pistons only ever break between the ring lands have never seen a broken skirt. I knurll the pistons when i do the head gaskets and somtimes when i rebiuld the engines if pistons where cheap and readaly avalible whould be different story i havent seen any weekness created by knurling have done it to turbo engines with nitrois and they always break between the ring lands nothing i could do to the piston can match that weak link. I have coustomers that have put over 100000kms on knurlled pistons and no slap. and none that burn oil i think that the piston being straiter in the bore prevents theese problems rather than creating problems.

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The 2.5 stroker turbo engine is a dissposable race engine just for doing drag race runs its high comp turbo engine its desined to run four 200 ft pasess and tear it down. Here is the beuaty thing about it total cost is set rod berrings main berrings and thats it rest is used free parts cost me 150 $ for 2.5 race engine that i dont have to care about in any way and makes good hp and tourque

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Had one come back knocking will c if is piston or failed rod did headgaskets and knurlled 2\4 about 50000 kms ago will get some pics of inside engine has 250000 miles on it should have done rod berrings but customer said no i will see how pistons held up or if knurling caused failure

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Love it!

 

great way to take up about 6-8 thousandths in diameter.

From what this machinist learned in school, (never done knurling on a piston, but have on a small shaft on a manual lathe), it raises the metal inside the knurl AND actually is more likely to increase the strength of the metal than fatigue it if done properly. Very little if any burrs will be raised, but some minor lapping (sanding) to fine tune the knurl easily can take car of that.

I can imagine it would allow for MUCH better lubrication.

 

Would like to see a pic of your air powered knurling machine Ivan...sorry lol I found the pic very cool!

Nice post.

 

here's someone elses writeup:

http://www.pbase.com/stealthfti/image/53355694

Edited by glkiller2

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got the engine apart funny i knurlled 2\4 and it threw rod on #3 pistons where fine non of the knurl had worn off and the cly was still good the engine had just been overheated and had worn berrings. I think rods and mains every headgasket job is a bitt extreme but may be neccasary to inshure qaulty job. Total time from running to crank on bench 2 hours 45 min.

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