The gudgeon pins might actually be the syptom, not the cause.
Observe the later 1994 4.0 I6 Ford crankshaft.
http://img.photobucket.com/albums/v223/ ... terwei.jpg
In 1990, Aston Martins Tickford development company did some engine developement on the Aussie EB 3.9 liter Ford I6 six. That engine is basically the 1968 US 250 with an overhead cam conversion. Pistons, crank, rods, gudgeon pins, main bearings, crank pins, flywheel and balance were similar to the US 250, only the deck height of the piston and block was taken down from 9.469 to 9.22" tall. Pistons compression height was reduced from 1.5 ish to about 1.375"
The English Tickford concern (who did the Aston Martin DB7 supercharged 3.2 development ) found that the crankshaft design was about 15 years behind BMW's and GM's, and that was the limiting factor to the engine not being repeatidly reliable for power over 225 hp or 5000 rpm. That wasn't to say the I6 was unreliable, just that it wouldn't hack the 300 hour, 50000 mile Test cycle demanded by Ford.
In my discussion with some Ford mechanics, from evidence from engine rebuilders, the bigger 250 style engine had significantly more vibration than the smaller 200 engines, and that was what created other problems. A trend from the early 200 engines to the later 250's, was less reliability per unit sold. By 1986, there were a host of niggling problems regarding detonation related issues, which were thought to be traced to the level of timing advance. By 1994, Ford had totally re-engineered the crankshaft on its OHC engines to eliminated other problems.
The fact that GM-H (Holden Australia) had started using 12 counterweight cranks in there larger 3.3 engines since 1980. The smaller 2.85 liter six ran the old 10 counterwieght iron crank for the rest of its life. That its archaic 3.3 liter engine was always a far smoother, free-er reveing and sweeter engine tan the 2.85 and earlier 3.3's had been observed since that time. In 1980, Holden made no changes to its 1963 engine aside from the crankshaft and head, and there was a con rod beam quality upgrade, but it still ran tiny thin steel 0.866" gudgen pins.
Reliability of the Holden 3.3 engines with a fully counterweighed crank was much greater. Old 3.3 (202) Holdens with iron cranks vibrated at 4500 rpm. With thew 12 counterweight crank, it was over 7000 rpm before a critical vibration period. There used to be a steel crank used in the triple carb and 2-bbl 3.3 engines. It is replaced by the cast iron 12 counterweight crank any time the engine is likely to be extended to 7000 rpm in a racing environment.
This is why I think, in a thin wall OHV 250, that the crank should be changed, and its my contention that it alone will eliminate the problem with gudgeon pin, cylinder wall, and rod failure, since I'm adament that its a crtical torsional vibration issue, and not a problem with the rods.
Old used Aussie 12 counterweight cranks are around for not much money. Anyone from 1997 back to 1994 could be used. It's possible that the stock 250 iron crank could be rewelded with 4 extra counterweights...it used to be done on some smaller engines. In our I6 framework, once you've added about 12 pounds of iron to the crank, it will raise the critical vibration period right out of anything likley to be used in your Turbo 250. A dual mode balancer helps too. The vibration on I6's increases proportionally, and then gets critical like a tuning fork. Like the onset of detonation, you won't notice critical crankshaft torsional vibration in a drag racing setting, but you would on a dyno with just some simple detection equipement. (I've had some background vibration detection equipment with this from my 7 years work in a laboratory and also from mine expolsion monitoring back in 1993).
As for wreckage, adams mates Turbo engined I6 Xflow might not be related to vibration, but I think the other pictures are, and I have found that breakages are not uncommon
http://img.photobucket.com/albums/v223/ ... nmajor.jpg
http://img.photobucket.com/albums/v223/ ... etBent.jpg
http://img.photobucket.com/albums/v223/ ... utabed.jpg
My opinon is that this all eminates from the crank, not the quality of pistons, rods or block, which are far superior to most of the GM L6 stuff.
