Dang!!! Busted a KB piston KB197 std 4.00" bore with the 12cc D-dish and old style single valve relief. Keith Black no longer makes this piston and new style is 25 grams lighter. Anybody got one?
You need to have a machinist turn a steel dowel that will give you the 25 grams that you need. This will be turned to be a interference or press fit into your current wrist pin. ***emble with red loc-***e. To be absolutely certain all is OK when you are finished, have the machinist mic the wrist pin in 3 places accross the length all at 90 degrees from one another, for a total of 6 measurements. Hone the rod small end and piston bores, only if needed, clean and re***emble. Yes I quarantee this to work and be 100% acceptable.
Thanks for the replies. The dowel suggestion sounds great. I was hoping that there was a chance that someone might have a matching piston.
Not unless the guy that said it doesn't know how to build an engine. To the O.P.: Worse case scenario you could always have 1 piston custom made.
Why take a chance on the other 7 buy a set and freshen the rest of the engine. I always seem to do it the hard way, 383 is a very good engine makes good tq #s and thats what moves a car.
A whole new set of KBs aren't that expensive. Check your other pistons for cracks, you might be surprised to find others getting ready to let go.
I don't know ow how the piston is broken, but if it is separated at the ring lands as in the top is separated from the bottom it is likely that over revving did it and the others are probably on their way out as well.
I imagine you used the 400 rods. If so, now would be a good time to upgrade to a 6" or at least a 5.7" rod (stock in a 350). Part of the problem with using the 400 rods the piston would **** in the bore and crack the skirts. If this is not the case, forget I said anything.
I won't forget, I was not aware of that particular problem and will add it to my build it right book.
I have the same question, whatever broke that one will eventually break the others!! The KB Hypers aren't bad pistons but you need to know the pitfalls. First, the end gaps on the rings are critical, second, detonation could be the culprit, they don't like detonation all (I realize no pistons do), and you still have a "cast" piston. You build the unit with those facts in mind. I haven't checked but I do believe that piston is still available?? Thanks, Gary in N.Y. P.S. This is a 5.700" rod piston, weighs about 515 grms with a pin that weighs 145 (these are all nominal numbers)
Ditto what he said. The ring end gaps are critical on those pistons. I always set them on the loose side.
Glad you put the little sarcastic icon after that statement. Otherwise someone might think you were serious. After racing for over 50 years,most of the time utilizing Chevrolet power I can't recall (when the rules allowed it) anyone using a shorter rod than the 5.7. the usual dimension is in the 6.0 range with some exceeding that. The 400 rod length was an effort to package a larger cube engine without changing the basic size of the small block engine. Worked well for the production applications the engine was ***igned to power. Leave it to the hot rodders to move things (dimension wise) to build a better "mouse" trap.
What does the old wrist pin weigh? Back when TRW still made engine parts there were lots of different SBC piston pins. Some long, some short, and some quite thick walled and heavy. the progressive size chart pages in the back of the paper catalog listed the dimensions and even the weights. I'd try to find a heavy pin before resorting to slugging a wrist pin. Here's a 131 gram Wiseco http://www.summitracing.com/parts/WIS-S718/ here's a 104 http://www.summitracing.com/parts/WIS-S643/ If this link come up 0.927 inch dia pins are available from 104 to 137 grams http://www.summitracing.com/search/...iameter-in/0-927-in/?Ns=Rank|Asc&autoview=SKU
As to why the piston was busted; the Dumb A** (Me) putting the short block together had to pull the #8 piston to see where the #7 rod was hitting the block (not clearanced at bottom of cylinder) and let piston/rod slide out of block and into floor. Made a terrible sound when it hit and snapped the bottom of skirt off. Totally MY fault!!! Now I'm stuck with 7 new pistons and a short block collecting dust until I do something. And I did use the 5.7" rod and gapped top ring as per KB spec sheet. This is my street rod engine build and I wanted this engine to be nice. Nothing has gone right; too much main clearance on new Eagle crank, etc. May need .001 brgs! Turned out to be the build from Hell.
Open the top ring end gap .010 more then the spec sheet says. Those pistons are noted for the top rings expanding and touching and breaking the ring land. The last couple motors I've built with those pistons I opened them up an extra .010 and have had no bad side affects. Just my experience.
I'm not saying I run a short rod in anything, but here's short blurb by Isky. I was trying to find a dyno test between short and long rods showing absolute miniscule amount of power gained by this if any. Sorry to jack your thread... Tech Tip - 2005 Rod Lengths/Ratios: Much ado about almost nothing. Why do people change connecting rod lengths or alter their rod length to stroke ratios? I know why, they think they are changing them. They expect to gain (usually based upon the hype of some magazine article or the sales pitch of someone in the parts business) Torque or Horsepower here or there in rather significant "chunks". Well, they will experience some gains and losses here or there in torque and or H.P., but unfortunately these "chunks" everyone talks about are more like "chips". To hear the hype about running a longer Rod and making more Torque @ low to mid RPM or mid to high RPM (yes, it is, believe it or not actually pitched both ways) you'd think that there must be a tremendous potential for gain, otherwise, why would anyone even bother? Good question. Let's begin with the basics. The manufacture's (Chevy, Ford, Chrysler etc.) employ automotive engineers and designers to do their best (especially today) in creating engine packages that are both powerful and efficient. They of course, must also consider longevity, for what good would come form designing an engine with say 5% more power at a price of one half the life factor? Obviously none. You usually don't get something for nothing - everything usually has its price. For example: I can design a cam with tremendous high RPM/H.P. potential, but it would be silly of me (not to mention the height of arrogance) to criticize the engineer who designed the stock camshaft. For this engine when I know how poorly this cam would perform at the lower operating RPM range in which this engineer was concerned with as his design objective! Yet, I read of and hear about people who do this all the time with Rod lengths. They actually speak of the automotive engine designer responsible for running "such a short Rod" as a "stupid SOB." Well, folks I am here to tell you that those who spew such garbage should be ashamed of themselves - and not just because the original designer had different design criteria and objectives. I may shock some of you, but in your wildest dreams you are never going to achieve the level of power increase by changing your connecting rod lengths that you would, say in increasing compression ratio, cam duration or cylinder head flow capacity. To illustrate my point, take a look at the chart below. I have illustrated the crank angles and relative piston positions of today's most popular racing engine, the 3.48" stroke small block 350 V8 Chevy in standard 5.7", 6.00", 6.125" and 6.250" long rod lengths in 5 degree increments. Notice the infinitesimal (look it up in the dictionary) change in piston position for a given crank angle with the 4 different length rods. Not much here folks, but "oh, there must be a big difference in piston velocity, right?" Wrong! Again it's a marginal difference (check the source yourself - its performance calculator). To hear all this hype about rod lengths I'm sure you were prepared for a nice 30, 40, or 50 HP increase, weren't you? Well its more like a 5-7 HP increase at best, and guess what? It comes at a price. The longer the rod, the closer your wrist pin boss will be to your ring lands. In extreme situations, 6.125" & 6.250" lengths for example, both ring and piston life are affected. The rings get a double whammy affect. First, with the pin boss crowding the rings, the normally designed space between the lands must be reduced to accommodate the higher wrist pin boss. Second, the rings wobble more and lose the seal of their fine edge as the piston rocks. A longer Rod influences the piston to dwell a bit longer at TDC than a shorter rod would and conversely, to dwell somewhat less at BDC. This is another area where people often get the information backwards. In fact, this may surprise you, but I know of a gentleman who runs a 5.5" Rod in a 350 Small Block Chevy who makes more horsepower (we're talking top end here) than he would with a longer rod. Why? Because with a longer dwell time at BDC the short rod will actually allow you a slightly later intake closing point (about 1 or 2 degrees) in terms of crank angle, with the same piston rise in the cylinder. So in terms of the engines sensitivity to "reversion" with the shorter rod lengths you can run about 2-4 degrees more duration (1-2 degrees on both the opening & closing sides) without suffering this adverse affect! So much for the belief that longer rod's always enhance top end power! Now to the subject of rod to stroke ratios. People are always looking for the "magic number" here - as if like Pythagoras they could possibly discover a mathematical relationship which would secure them a place in history. Rod to stroke ratios are for the most part the naturally occurring result of other engine design criteria. In other-words, much like with ignition timing (spark advance) they are what they are. In regards to the later, the actual number is not as important as finding the right point for a given engine. Why worry for example that a Chrysler "hemi" needs less spark advance that a Chevrolet "wedge" combustion chamber? The number in and of itself is not important and it is much the same with rod to stroke ratios. Unless you want to completely redesign the engine (including your block deck height etc.) leave your rod lengths alone. Let's not forget after all, most of us are not racing at the Indy 500 but rather are hot rodding stock blocks. Only professional engine builders who have exhausted every other possible avenue of performance should ever consider a rod length change and even they should exercise care so as not to get caught up in the hype.
I used the 5.7" rod hoping this would cut down on cylinder wall wear. May not help at all. Does anyone else open up the top ring gap above the .0065" per inch of bore KB recommends?
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