DDK - Die Deutschen Klassiker

Sorry, should have looked back. Check the weight difference and if there’s much difference, careful grind away judiciously.

Forged vs cast ..... you will not regret using forged pistons, you could regret opting for cast.....I don't really see why piston slap should be there with the JE pistons....im hoping someone can explain. W

Unless the clearance in the barrels is different on the JE cylinders... if this is that case id still want to know why?

Winston I believe it is because the JE piston have centred gudgeon pin location
and others have offset pin location which keep the pistons in line better.

Karl

The shorter piston skirt?

“Piston slap is generally caused when the cold running clearance (piston-to-wall clearance) is large enough that when the piston rocks from side to side in the bore it “slaps” the side of the cylinder and causes noise,” explains JE Pistons’ Clayton Stothers. In the case of the LS, the shorter piston skirt meant that the angular shift of the piston in the bore was more pronounced than with a longer piston running the same clearance. To make matters worse, that clearance couldn’t be tightened due to the fact that even with cast-in iron sleeves, the early, aluminum LS block wasn’t as dimensionally stable as an all-iron small block Chevy.

Sent from my M2004J19C using Tapatalk

Thanks Neil
Every day's a learning day.

Karl

OK, so do you want to hear what pistons slap sounds like on a cold engine? This is worst case scenario as the Type 4/914 engines are notoriously noisy due to their aluminium cases (ie, no magnesium content) and mine has aluminium-finned Biral cylinders, which also transmit more noise. Ear plugs at the ready? OK, go!

https://youtube.com/shorts/k8mpR3t0JXY

And, yes, it does quieten down as the engine gets warm and/or as the revs increase.

Hi Keith, my T25 sounded just like that, and it went away with revs, and/or load.......t'was a big end.....

That's a cheery thought. The engine, pre-rebuild, sounded like this but later developed a slightly different 'knock' separate to the piston slap, which was number three rod bearing (sorry, big-end) on its way out following ol starvation problems. If you do a Google search on 'JE piston slap' you'll find endless posts on various forums (Hondas, Chevies, Fords, you name it) all cataloguing rattly engines ('my engine sounds like a diesel' is a common one). Even JE acknowledge it as per Neil's quote from their website.

Sadly my T25 has Mahle pistons!!

Thanks for the video Keith.
It's not the same but reminds me of my old Honda NSR 250 SP
that had a dry clutch and would rattle like hell in neutral.
The amount of know it all's that said "that needs looking at" was funny.

I got a set of digital scales to start balancing things up.
Just a quick look to see the difference between old and new.
Saving the weight of just under half a wrist pin per cylinder....

20220628_171309 by karlhash, on Flickr

20220628_171818 by karlhash, on Flickr

Karl

Its been slow going in my garage lately, too many family chores for Porsche progress.
To my surprise whilst hard at work making bedroom furniture for my son, the rest of my parts turned up.

20220809_173844 by karlhash, on Flickr

I know I could have made much better use of the time waiting for them but I'm in no rush and I don't want to let it become a stressful thing so no deadlines.
First task so far was to take the crank and clean it. The packaging it arrived in had disintegrated leaving it covered in bits of dried crumbled foam.
I took out the grub screws from the cheeks of the crank to clean it internally as ignoring this will lead to contaminated oil and ruin your brand new engine.
I will definitely try to avoid doing that.

20220809_173856 by karlhash, on Flickr

debris inside crank
20220829_171046 by karlhash, on Flickr

the black marks in the red tray are what came from just one hole..!
20220829_175014 by karlhash, on Flickr

haha, I'm making you check out my clean orifice
20220829_175052 by karlhash, on Flickr

stage one of crank clean, its far dirtier than I thought, still.
20220829_183609 by karlhash, on Flickr

Karl

A little more progress from me.
I took the conrods off the old crank.
The bearings look to be about worn out but that's not bad going if the date on them is any indication as to when they were installed.

20220910_153544 by karlhash, on Flickr

It took precisely 7 mins of heating the timing gear with a torch flame before it would budge, but once warmed up it wasn't too difficult.

20220918_160850 by karlhash, on Flickr

20220918_165933 by karlhash, on Flickr

Old non counterweighted crank weight
20220919_143442 by karlhash, on Flickr

new counterweighted crank weight
20221001_161054 by karlhash, on Flickr

I was expecting a heavier weight from the new crank as I had read somewhere that it would be 10kgs so I'm quite happy that the engine will spin up in a similar vain to before.

I weighed my con rods end to end and matched them all to within 0,1 of a gram but that was total weight and one of them had a significantly lighter big end so I will have to re do them to satisfy myself.

20220924_161833 by karlhash, on Flickr

I tried the flywheel fitment to the new crank and because I have been reading every engine build thread on 912 BBS I had prior knowledge of the problem I encountered.
The new dowel pins on the new crank are about 0.2mm bigger than the pin holes in the old flywheel.
I did what the person from 912 bbs did and pulled the flywheel onto the crank with the gland nut which left a burr in the flywheel holes. Cleaned them up with a reamer and job done, nice snug fit.

20221002_170900 by karlhash, on Flickr

Next I weighed all the pistons, gudgeon pins rings and clips. Putting all the heavy clips and rings with the light pistons and vice versa.

20221008_151208 by karlhash, on Flickr

Then I checked and filed the ring gaps and side clearances but I didn't have a feeler gauge thin enough for the minimum clearance so I went round measuring paper but even those were too thick.
In the end our cheap kitchen foil was just the right size

20221015_121452 by karlhash, on Flickr

20221009_171500 by karlhash, on Flickr

20221015_131835 by karlhash, on Flickr

Next up is work on the heads. I had a chat with Angus and Sam at Greatworth Classics and Simon Rudge on Sunday at the meet up and they were most helpful. They deduced I needed to find a machine shop so I have asked for some quotes for the valve guide work needed and crank assembly balancing.
I will let you know the outcome.

Karl

Nice work Karl

Very nice photos as well Karl. I must say those dowel pins clearance issue has me thinking is that correct? The 0.2mm oversize you mentioned seems excessive to allow dowel pins to be forced in. Did you mean to write 0.02mm oversize on the bore size?

Roy