Porsche Enthusiasts Club Forum

The art of engine building, and what sets a well build engine apart from a poorly built engine is to assume nothing.

I have seen new conrods being out of round both before and after the bolts have been torqued down.

Very few people these days dummy build things up as part of the build process. Typically we spend a minimum of 40 hours assembling a 911 engine, and that assembly time includes dummy building, thread chasing, fettling, repeated checks of measurements and disassembly and reassembly. This does not include the stripdown, cleaning, initial measuring or machining. Obviously this time is slightly less on a 944/968 engine, and quite a bit less on a 924 engine. But the same fundamentals are important.

The problem is, few people want to pay to have this kind of care and attention to detail, so we sometimes have to comprimise our desire to do things right to match the budget of the customer, obviously with the correct disclaimers and warnings... However, I do hate doing this and am constantly on the brink of deciding "if you want corners cut, go elsewhere", but for the time being, we try to be accommodating.

I could have bought another decent 924 for the money I have already spent on having the full engine stripped down, chemically cleaned, flywheel and clutch cover lightened. And so far nothing to show for it!! (hope the head is OK for you Jon!?)

I have estimated the cost of the bottom end ingredients needed for the rebuild and I won't see much change from £2000. No idea what the machining, balancing and rebuilding is going to cost but I am sure I'll feel the pain. All this before I even install, tune, run in, re tune, fettle, tune again, dyno, tune, dyno, phew!!

I just want to drive and enjoy it!!

Stripped the front end some more for repainting

Very interesting read. I'd be tempted to put a 951 motor into a 931 shell. Make a sleeper. That would be fun. Not sure if all the pickup points are the same. Pretty sure you can do this on an 944 n/a without major dramas. Wonder what happened to that guy Steve wasn't it, with the highly developed Orange 931 with ITBs etc? That looked like an impressive little beast.

Hey Steve, you CC'ed that head yet?

The head you dropped off to me will be fine, will be going to good use.

Putting a 951 engine into a 924S is quite easy, the 924 and 924 turbo shells are a bit more tricky, but not impossible.

I love a good street sleeper like a well tuned 924 which still looks period, as much as a love an all out "in your face" racer such as a 968TurboRS.

I think the 924 turbo engine is an untapped item, as is the 951 engine.

Hi Jon. Been waiting for the engine builder to give me the deck height measurement. I was expecting a figure from crank centre to top of block between 230 and 232mm, is this correct? What I received was 179mm!?

As for CC'ing the head, I have been working flat out for the last few weeks so haven't got a chance to pull the head myself and measure. Hope to do it this weekend. I have two heads which both have been refurbed so will do both.

Was going to use this 'how to' http://www.924board.org/viewtopic.php?t=36848 any other watch outs in the process?

No problems Steve

I wanted to make sure I had not missed a message from you, its all good as long as we are waiting on you, would be aweful if you thought they were ordered and were waiting for them to turn up!

That method for CC'ing the heads is fine, not read through it, but it seems to be what I do, not sure if they included the head gasket thickness and gasket bore size calculation to add to the CC, but I guess they have included that in the howto.

Good point on the gasket Jon. I can't remember reading the head gasket measurement. I have picked up a stock Victor Reinz HG so can add that to the measurement.

Back to the deck height measurement of 159mm (this is centre of crank to top of block), does this sound right? Any idea what it should be? I can only find a measurement given to me by Ideola re his Diamond pistons which stated 230-232mm. Can you clarify what the crank datum point is. Clearly the top of block is the easy part to find!! Dan suggested

top of the block down to the centreline of the crank.

With the gasket, typically I used to find a 924 turbo standard headgasket will crush by 0.2mm with the head torqued down.. so subtract this number from the measurement of the thickness of the head gasket (measured at the outside, not the fire ring. From memory, I think they were about 1.2mm crushed, but that is just from memory.

That figure you have of 159mm seems too low. from memory, I could trawl through all my notes and technical data, but I really do think that is too low a number.

Thanks Jon. Called the shop, yes there was an error on measuring. The block measurement taking in to account a light skim/ surfacing of the block then we will aim for figure of 231mm dead.

Another one for you Jon, what's your thoughts on the issues with forged piston grabbing/wear due to too tight or piston slap if too loose a tolerance used. You always hear of the several piston failures, here JE, but not the 100's of satisfied customers. What's your advice to give my builder for my application?

http://www.924board.org/viewtopic.php?t=37291

To be totally honest, most of the people you see complaining of piston slap or pistons grabbing have a story to tell.

I tend to order custom pistons from JE, not off the peg ones.

I give them data, they send pistons with the correct bore to piston clearance for that EXACT application. They model the piston, simulate it, and only then do they make it.

If any engine in the world would grab or have piston slap it would be the 3.2 944 Turbo engines we built, they have a 108mm bore (yes that's massive) with an aluminium alloy forged JE piston, in a billet steel liner, sealed to the head with a bronze alloy pyramid ring to interface the head, within an aluminium block. In other words, you have several items all with dissimilar rates of thermal expansion, seeing massive amounts of stress, with no piston grab or piston slap.

On the other hand, you can not furnish them with all the data and have some off the peg pistons, such as 924 turbo oversize 1, or something like that, then get a really cheap machine shop to bore your block with a boring bar, and you crank ground by a place that also grinds cranks for the local back street garages and have the entire assembly put together by "X" who you met in the pub, or on a forum, and who should know what they were doing because their engine had a lot of bling... Then the owner of the built engine will start it up and will have his foot flat to the floor at 100mph even before the starter motor has disengaged... not long after that the owner of the car will post on a forum that JE make crappy pistons that slap/pick-up.

When the order for JE pistons is made, you give them all the details including the exact bore size, they design the piston, they make the piston, UPS ships the piston and when it arrives it will have a spec sheet showing their bore to piston clearance, which will be right, but it is worth checking it, if it picks up or slaps, you tell them off.. But I have never had to tell them off after ordering hundreds of pistons like this.

I would expect the bore to piston clearance they specify will be around 0.004X" But let JE Pistons worry about that.

I just read that thread on 924.org

Does anyone out there remember "beaker" out of the muppets? You know, the scientists assistant..

Ok, I said enough.

Thanks Jon, it's not a test your part with these threads, just to put to bed forum opinion. Yet again it's great this forum has technical expertise on hand

Noooo it's ok, just nearly every one of the posts you have linked to has the same muppets posting expert advice which is seriously flawed, especially that Ideola or whatever he is called and his amazing pistons designed for another car, which happen to have a completely useless piston crown design which he refers to as an innovative more up to date design... jeeezus

I bet if someone in there posts a question about "Pepsi versus coke" he will turn the conversation around to his amazing pistons and how every design flaw is actually a cunning design feature! lol Moron.

Syringes arrived this morning so its CC'ing the head time this weekend