engine and drivetrain Head crack from 10.0.1 pistons and stock 260 cam?

[EcoAuto]

I was told by a reputable engine guru (known in the 02 community for building high-performance ported and surface turbulence engines with forged pistons) that 10.0.1 cast pistons in an 02 block with e12 head and stock 260 cam can increase compression high enough to crack the head.

I'm concerned because my engine was showing compression of 150 or so, before having a valve job and head rebuild. I had the machine shop exchange the Schrick 292 for a stock 260 cam (from Ireland Engineering), to settle down the lumpy idle. After the engine compression went up to 195 all around.

Was this due to the cam change or perhaps the head shaving? Will 195 compression damage a standard 36 year old e12 head that might have been welded over the years? I was also experiencing run-on detonation on warmer days, even though the engine temp was midway between cold and hot. Using 93 octane fuel or 91 octane with octane booster.

I'm replacing the head and wondering if I should reuse the nearly new IE cam, or if I want to match the 10.0.1 pistons with another 292 cam.

[Guest Anonymous]

This will not cause the head to crack.

Compression at cranking speed will go up with the stock cam because there is a lot less overlap. This could also some what affect the pre-ignition. Prei-gnition can also be ignition timing and fuel mixture. It is usually most worst at full throttle in the midrange. You may have to reduce the ignition timing a couple degrees and maybe change the carb jets, What is the timing at full advance (over about 3200) and what jets are in the carb?

[EcoAuto]

It's a 74 Tii engine with a Kugelfisher FI, refurbished at Pacific Fuel Injection, and rebuilt injectors. The head is an e12. The distributor is new from Ireland Engineering's with IE Pertronix.

[eurotrash]

(ahem)

[TobyB]

I was told by a reputable engine guru that 10.0.1 cast pistons in an 02 block and an e12 head with stock 260 cam will increase compression high enough to crack the head.

We were also told that the world was gonna end some weeks ago.

I personally have not found any unmanned cars sitting around.

Overheating cracks heads, as long as nothing incompetent is done.

That, and maybe detonation, but usually it's the overheating.

t

[c.d.iesel]

.......ignition timing - with a strobe light

idle speed

idle mixture

spark plug heat range

[1453aalapapa]

where did you get the 10:1 pistons from? if they aint custom, they aint bmw. cause bmw dont have no e12 10:1. now, 121ti head DID have 10:1.

[EcoAuto]

Hi Ken,

The 10.0.1 pistons were already in the engine (with the Schrick 292) when I became the car's new guardian last year. I have paperwork going back to 1999, at which time a valve job was done at Road Rockets in Marin, CA. That was 50,000 miles ago (OD now shows 164K). The rebuilt tii engine must have been installed quite some time before that... probably mid 80's.

The reason I'm concerned is that I'm interested in a complete, recently rebuilt Tii engine (rebuilt by La Jolla Independent) that I came upon, and it has 10.0.1 pistons, a stock cam and e12 head.

[Todd21]

Ron,

Careful not to mix your units during this discussion. Compression Ratio (CR) is the volumetric change of the combustion chamber, while you are reporting the cylinder pressure during cranking.

As many here have stated the higher pressure you see is due to the overlap of the valve timing, but the CR is set by the change in the volume of the chamber and would remain constant for a motor. Over time, wear will allow for leakage at the rings, valves, gaskets, etc. producing lower cylinder pressure even though the CR is still the same.

HTH

Todd

[1453aalapapa]

Hi Ken,

The 10.0.1 pistons were already in the engine (with the Schrick 292) when I became the car's new guardian last year. I have paperwork going back to 1999, at which time a valve job was done at Road Rockets in Marin, CA. That was 50,000 miles ago (OD now shows 164K). The rebuilt tii engine must have been installed quite some time before that... probably mid 80's.

The reason I'm concerned is that I'm interested in a complete, recently rebuilt Tii engine (rebuilt by La Jolla Independent) that I came upon, and it has 10.0.1 pistons, a stock cam and e12 head.

la jolla independent has forgotten a lot more than i know, but i know there aint no bmw(mahle, kolbenschmidt, even nural) 10:1 for e12. is the engine AT la jolla, or someone else has it? if so, then probably custom pistons, but custom pistons are generally forged, not cast. road rockets is a quality shop, watson knows his 2002's. if the engine is at la jolla, i am sure they would stand behind their work. if the engine is somewhere else, you should call la jolla and ask them about it. 858 488 1555, carl nelson, owner.

[TobyB]

Sure there are-

just take the 9.5's and mill the head a bit.

There's 10:1!

(.7mm, maybe, just guessing?)

Mine with 9.5's and a full mm off is in the 10.3 range...

t

[EcoAuto]

Here's a birds eye view of my e12 pistons - ready for an engine rebuild. Piano pattern. I believe they're Mahle 89.22 MM(+0,25) P/N 11251261928

[TobyB]

hmm, no markings... I would have expected numbers stamped on the top

of the pistons (or are they just not visible in the pix?)

and you have the thicker gasket, there... I think stock was 1.3 mm...

I woulda said that a +.25mm piston would have been factory- only, but

that gasket's certainly aftermarket. Maybe it's a top- end job on a

factory short block.

All this said, I've only taken apart ONE engine that had pistons that

were remotely re- usable... in about 20 or so. I did reuse some that I

shouldn't have... and that worked out OK. Not great, but OK.

(as in, it didn't blow up, but it had higher leak- down at the rings than I would

have liked)

blah blah blah.

t

[EcoAuto]

I had the e12 head rebuilt at a local machine shop last year, and I supplied them with the rebuild parts, including that head gasket you see - which I bought from RMEuropean.com.

After getting very valuable feedback from you guys, I made a decision. Rather than rebuilding the head again, or buying a rebuilt head, I'm going with a complete Tii engine that was rebuilt by La Jolla Independent. An FAQer who decided not to install it in his 02, saw my post and offered it to me. It's a "plug 'n play" '74 with Kugelfisher, injectors, pipes, runners, manifold, starter, distributor, etc all included.

My other option was a Metric Mechanic rebuild. They have a 2200 ST HiFlow 155 HP for a Tii on hand, and are discounting it by $500. It's more engine than I need, and I had some concerns about the forged pistons. So I went with the stock La Jolla rebuild.

Photos of the La Jolla Independent engine I'm buying from Kurt Bicknell attached.