Page 3 of 5
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Fri Dec 24, 2021 12:32 pm
by coomo
PeterK wrote:The pistons will be fairly precise, although there may be a slight difference in rod bolts. If rods are different, then a slight fettling will see them right.
If you're doing it properly, balance the little ends so that they're all the same, then the whole rods by 'adjusting' the big ends. IIRC though, Porsche specify quite a large permissible variance - an inherent benefit of the boxer engine I suppose.
I had my complete bottom end balanced, so rods, pistons, crank, flywheel, clutch and front pulley. Will I ever be able to notice a difference - no chance, but the £2-300 was a drop in the ocean of total rebuild cost, and I can brag about having a balanced engine in the pub now
This.Set of SC rods cost me £40 to have balanced.When I mentioned crank balancing to Rob Walker,he sneered at me! As you say you may not notice a difference,however no one ever could, and the possiblity of an engine that spins more freely etc, is an unparelelled bagain for £300 in Porsche universe.
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Fri Dec 24, 2021 2:17 pm
by KS
JE pistons are notoriously noisy on start-up - in the case of the pistons I have in my (albeit four-cylinder) engine this is down to having zero pin offset, meaning piston slap is a way of life until warm.
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Fri Dec 24, 2021 3:29 pm
by 911hillclimber
A guy I 'know' rebuilds water cooled engines for a living locally, dead IMS Boxsters etc.
He really does not like JE pistons, but he has advised having then coated to give the skirts a fighting chance. Not sure if this could stop some slap?
As this is a race only engine not too fussed, but for £300 maybe worth it. He knows a place that does this 'ceramic' coating process.
Hope to get the pistons in 2 weeks.
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Fri Dec 24, 2021 5:33 pm
by KS
My JE pistons already have coated skirts but still slap. I was worried at first but soon got used to it...
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Sat Dec 25, 2021 9:57 am
by coomo
911hillclimber wrote:A guy I 'know' rebuilds water cooled engines for a living locally, dead IMS Boxsters etc.
He really does not like JE pistons, but he has advised having then coated to give the skirts a fighting chance. Not sure if this could stop some slap?
As this is a race only engine not too fussed, but for £300 maybe worth it. He knows a place that does this 'ceramic' coating process.
Hope to get the pistons in 2 weeks.
By the time £300 is added on top of the JE pistons,arent they going to get pretty close to Mahle cost wise?.
Im no expert beleive me, but i cant see how some ceramic coating would negate happy slappy pistons.it would appear the the word "ceramic" can now be used is a myriad of coatings/treatments and processess,with some wonder properties and a cure all for all things mechanical.Last time I usec a ceramic coating( on a turbo) it fell off after 10 minutes.Not that my process may not have been to blame.
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Sat Dec 25, 2021 7:07 pm
by MikeB
Have to say no slap from my 10.5 Wossners, just pulled them out after 6-7k miles of spirited motoring and the ceramic coating is generally intact.
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Sat Dec 25, 2021 7:21 pm
by 911hillclimber
The local engine rebuild man said the coating originally on the JE Pistons almost wipes off, and so they have the Pistons treated to this coating, not sure what it actually is.
Seem hard to see that JE over all these years would have a piston design that slaps.
Imagine the complaints.
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Sat Dec 25, 2021 7:33 pm
by PeterK
My understanding is that this is due to the piston material’s rate of expansion.
If the piston is the correct diameter at operating temperature, it will be slightly too small when cold - hence the slap on start up. This is apparently an acknowledged ‘feature’ of the JE pistons
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Sat Dec 25, 2021 9:01 pm
by 911hillclimber
At least I won't fall over when the engine knocks on first start!
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Tue Dec 28, 2021 9:31 pm
by RobFrost
If I remember correctly, according to a video I saw (possibly Heidi and Franny) you need to put some plasticine around the edges as that's the narrowest spot. Obviously depends on pistons etc.
Sent from my SM-G988B using Tapatalk
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Wed Dec 29, 2021 9:10 pm
by 911hillclimber
Correct, many use simple pellets of plasticine esp around the piston head outer top surface, but really about 5 pellets across the side to top back down.
You bring the piston up to the head with the pellets crushed when tic is reached.
Strip the engine ( only one cylinder) and measure the thickness the pellet s have been crushed to.
That thickness needs to be about 80 thou.
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Thu Dec 30, 2021 8:10 am
by gridgway
Presumably you have two types of possible contact. One is between piston and head and then between piston and valves. Do both have to be checked?
Checking valve/piston clearance is more complex I guess.
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Thu Dec 30, 2021 9:00 am
by PeterK
Yes, both need to be checked.
Two ways for piston / valve clearance. Firstly you can use plasticine or cored solder (the core makes it more easily compressible) in a similar way to the head / piston check. The other way uses the fact that one turn of the tappet adjuster is 1mm. With a piston at TDC, wind in the tappet and see how much clearance you have. Worth repeating this at 5, 10 & 20' before and after TDC.
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Thu Dec 30, 2021 9:52 am
by gridgway
I've never built an engine that has valve piston chance checks needed. But presumably it can be complex as you have a moving piston in conjunction with moving valves. Only if you want to maximize stuff though.
Re: JE Pistons, 11.5 cr into a 3.2 flat 6?
Posted: Thu Dec 30, 2021 10:10 am
by PeterK
Always recommended if you have either non-standard pistons or camshaft. Especially if you have both, like I did, although my clearances were fine.