How did this engine stay together for 14 passes?

Frank has a nice two-bay shop.

 

Boss 302 pistons were famous for that. I think ford actually redesigned the piston skirts because they had so much trouble. I had that tick in a 70 boss 302 and had 3 broken piston skirts and with mechanical lifters it was hard to figgure out I kept measuring and checking push rods I thought everything but the skirt until someone told me it was a common problem.

 

I've seen a few do that too. All of them (that I saw) were cast pistons. I work on smaller engines daily and it happens a lot when the bores get worn, pistons get worn, or you start hammering the engine before it's warmed up.

Old Guy is right about keeping weight to a minimum. You should see the internals of some of the later model stuff, even though it's bone stock, its trick! One engine comes to mind....the Yamaha 450cc motorcross bike 4 stroke motor. everything is super-lightweight. Rod is small, big end is smaller than a normal 125cc engine, flywheel is small & light....the piston...jeezus that thing can't be considered a piston, it's just a ring holder with a wristpin stuck through it. It's maybe 1" tall from the bottom of the skirt to the top of the crown, but it's light. Hollow cams, 5 titanium valves....etc. Speaking of cams & valves, I have one of these heads here at home and I was looking at the port work and shapes. Man, if someone ever comes up with an automotive V8 engine that has ports that are this nice, they're on the way to a handful of horsepower. Keep in mind that these things are making 50+ HP out of 450cc, at 13,000 RPM. I've seen as much as 68 on a blueprinted/modified version. Pretty stout for a bike that weighs just over 200 lbs.

IMO, if you must do block work, it's almost the same price to just get a 347 crank/rods/pistons as it is to just go back with the 289 or 302 stuff. In my edumacated opinion, I'd think real hard about going with a 351w based engine, but that's me. If I had the room to put it in there, I would NEVER go with a 302 again. The 351w is a much better design from most standpoints. Only thing a 302 has is lighter weight and it's smaller & able to fit in our tiny Maverick or Comet engine bay.

BTW most of your 347 stuff will use really short pistons and 5.4" rods. Some are using 5.3" rods to keep the pin out of the oil ring, but if the pistons & rings are properly assembled, oil control is not an issue. Every 347 I've seen revs REAL quick due to the light weight.

 

That may be part of the problem. My old Ford Performance book, written by Pat Ganahl (published by S-A Design) says that the 302 block is preferable for use with a 302 crank because the cylinder bores extend a little further at the bottom to provide a bit more support for the pistons at the bottom of the stroke...

 

That's just it...until I get the crank out, I'm really not certain what it is. I've just assumed it was all 302 until now. I'll post when I know the results.

 

Wow, I'd say you had some pretty good luck!!

 

The funny thing is that forged or cast pistons didn't make a difference when the problem was at it's peak.
I think it is not as common today because changes were made in the parts. Even the B302 service pistons got the ribs added, and that was early on in the history of the engine.
New engines were doing it back in the 60s-70s, so it probably has more to do with the oversquare nature of the engine and lack of foresight among the engineers that designed the pistons.
It seems it is not so much a problem since the aftermarket has taken to the engines in the 80s.
I hate to say it, but Ray probably had some old pistons in there.

Every stock 302 I have ever been involved with a teardown, has had some piston skirt cracking. I cannot remember any cracks on any overbored (new pistons) engine I have taken apart. That leads me to believe it was either a stock piston problem, or at least a parts problem that has since been recitfied.

That said, this is the first failure I have seen. I knew it happened, but have never seen the final product. It surprises me that it is such a catastrophic affect on the piston.

Dave

 

Mine never cracked /broke like that, only the narrow part of the skirt broke

 

I built my first engine in '83. Had the block bored .030 with TRW L-2350 forged flattop pistons. Ran it on the street hard for two years before I started racing it. Spun a bearing in '86 so I put in a new crank with two new rods, new rings and bearings. Went to a race at the first of '92 (drove it) 200 miles away. The first time that I started it after returning (a couple of days later) it was tapping/knocking. When I took the pan off there was one skirt in the pan. I dont remember if it was the whole skirt or part of it, but a couple of more had cracks. I built another engine at the first of '92 with a fresh .030 overbore with TRW L-2482 ( I think they superceded the 2350s) forged flattops. It dropped a valve at a race at the end of '93 and locked up. When I tore it down there were two or three pistons where the skirts had started cracking. I built another engine at the end of '93 with .040 Keith Black hypereutectic pistons. It has been driven and raced regularly until the end of '03. It has never been torn down and is still running today with no evidence of skirt breakage (no tapping/knocking).

 

Thanks for the info. I had pretty much decided to go with the Keith Black hypereutectic pistons and you just finalized it. Now I just gotta check the cylinders to see if I need to go to 040 or not. It looks great but looks can be decieving so I'll let the machine shop check it as soon as I get finished tearing it down. That will also help me to decide on stroking it or not.
Thanks again, Ray

 

It wasn't until after I bought my KBs that I started hearing the horror stories about the top ring lands breaking off. The person doing my machine work assured me the pistons were fine. They just needed extra clearance in the top ring gap. The instructions with the pistons called for .026 for a street engine on gas and .030 for a drag engine on gas. I gapped mine at .026 (except for one .028-got a little carried away with the grinder). I have also heard that they do not like detonation, although I have heard my engine detonate on occasion.

 

Been abusing my KB pistons for many years and 2 blocks . Just have to have more ring gap because they swell and contract a bit more.

 

I think I might have mentioned that at the r-up.(the noise sounded familar) I had a set of trw pistons that did the same thing. good thing you found it before it blew.