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Hello. I have been lurking here for quite some time, but now have run across a dilemma I cannot seem to resolve, so this is my first post.

I am in the process of a complete rebuild of my Deutz f3L912. Turned crank (all journals 0.010" under) and rods installed with all bearing tolerances nicely within spec. Original cylinders still within OEM dimensions, so I merely honed and installed MEMO pistons. Block, head, and cylinder mating surfaces were well cleaned.

Using a 0.3mm shim and 1.2mm fire ring, I have what looks to be 0.09 (2.286mm) piston to head clearance (more than double what I see as recommended, i.e., 1.0-1.2mm (0.03937008" - 0.04724409")). I can reduce this a little by replacing the shim and fire ring, but to the best of my knowledge, the thinnest available is a 0.2mm shim and a 1.1mm fire ring. Those will save only 0.2mm, so I will still be well over the 1.0 - 1.2mm recommended range.

Not sure why this clearance is so large or how best to fix (suspect the crank throw and/or piston height must be off). I suppose I could mill things, but I'd prefer a simpler resolution.

I'd appreciate any opinions/experience on how bad this engine would run if I copped out and accepted a piston to head clearance of 2.086mm (roughly 0.08").

What should reasonably be considered the max acceptable piston to head clearance?

Has anyone run across this problem? Any ideas or suggestions will be much appreciated.

Thanks.

lld1948
 

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I take it the .3 shim and 1.2 fire ring were what was installed when you pulled it down.
Only change you have made is the pistons so suspect they are not the same height as the originals..
Were the new pistons for a turbo motor?
Been a long while since I was into a Deutz, is the shim actually needed?
Best guess is you will be only slightly down on compression
 
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Discussion Starter #3
Thanks for the insight. Yes, the .3 shim and 1.2 fire ring were original. Your suspicion was logical (that the issue was with the pistons), but was based upon faulty information (which I had provided).

I discovered the problem, and am embarrassed to say what it was.

A certain young fellow was helping me (he is actually a pretty sharp kid). I was called away as we were preparing to mount the first cylinder. When I returned, I was impressed - he had the head installed and fully torqued (so I was hesitant to remove it). We checked the clearance several times by inserting solder through the injector bore, both on the exhaust side and the service side. We consistently measured nearly 0.1" clearance. After considerable head scratching, that evening I posted here for the first time.

Then I slept on it. When I got back to the project, I removed the head. Duh! We'd installed an extra fire ring.

So, in the words of the late Rosanne Rosanna Dana, "Never mind." But thanks for responding.

To answer your question, according to the manual at least one shim is required in order to make a proper seal.

FYI, I did polish the cylinder/head interface slightly, and am finding that, in addition to the 1.2mm fire ring, and the 0.3mm shim, I need an additional 0.2mm shim. With the additional shim, the largest crown measurement is right at the max spec'd range (1.0-1.2mm), while the smaller measurement is in the middle of the range. Averaging the two measurements (this is proper, right?) I have a crown clearance of 1.13-1.15mm, which is a good place to be, I think.

Without the 0.2mm shim, it looks like crown space would be less than spec'd. I am now wondering if the clearance was smaller before. If I had it to do over, I'd have measured the crown clearance before dismantling the engine (something I'd recommend to others who might endeavor to engage in a similar folly, just for informational purposes).

Anyway, thanks for responding. It's good to know there are folks out there who will reach out to help resolve even self-induced dilemmas.

LLD
 

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Glad it is sorted.
Checked around online and found a site that had a fair explanation on shimming, they also make various size fire rings.
Know the feeling of others getting involved, had a 16V71 GM reworked and went to fire it and water came out the rear airbox's on the left side.
Another mech had fitted the head without the fire rings/head gaskets. Not fun telling the boss they could not start work for a couple of hours till we had installed new gaskets
 
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