then is it likely to cause a balance problem using rods and pistons that are lighter than stock?
It will not cause vibration but may change the main bearing loading some.
There is very wide variation on how single cylinder bob weights are calculated,( the difference is it changes the direction of vibration) so I doubt that it would be very sensative.
If you look at most cranks that are naturally balanced the cws are smaller than would be reasonable if it were a one cylinder so in all probability with lighter parts you are going to reduce bearing loads both from lighter parts and being closer to balance.
-what do you do about inline 6 cylinder cranks when balancing them?
-Do you have to make up bobweights and if so do you use the same 50% as you'd use on a V/8?
-I have a Jeep 258 crank to balance and just realized that I've never built nor balanced an inline 6 in all these years.
[quote="bill jones---------------------------------------------------------------------
-Here's another deal:
-I have a friend who runs a VW rabbit pickup truck at Bonneville with a 2000CC (122ci) cross mounted front wheel drive water cooled engine.
-He decided that he wanted to run in a class that allowed 1000cc's or 61ci so he took the rods and pistons out of two cylinders that went up and down at the same time, ground the lobes of those two cylinders off of the camshaft, then he installed a pair of radiator hose clamps on those two empty rod journals to cap off the oil holes.
-This engine shakes super bad at idle and below about 4000rpm but at 4000rpm he says it smooths out and he run it up to 8700rpm during two consecutive runs and he established a record at 96 and something MPH.
-We had talked about it that's what I told him I'd do.
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-Then he put the 4 cylinder engine back in and went out to run and everything broke, like the bellhousing broke, then after replacing the the bellhousing the stock clutch came undone on the next run.
-It's like that 2 banger's power pulses are so far apart that it acts like a jack hammer.
-Now for sure we had no idea what to do about the two empty rod journals but I personally do not believe that the crank balance had anything to do with the breakage of the parts.[/quote]
About 20 years ago when I built my Bonneville streamliner I had no idea how it would handle and as I thought ithad 200mph potential (eventually went 280 or so) wanted to start out slow. Power was also 4 cyl 122 ci. The 1 liter (61ci ) record was open at the time so what the heck. I took 2 piston/rods out. In contrast to Bill's engine above, I left the back two in. I made bobweighrts with a bearing in center so looked like a donut for rotation and oil control. I think they were 50% but don't remember now. Cams too valuable with the DOHC engine but had some trash valves so cut the stems off so lobes would clear and left out the tappet buckets. We using a more or less dialed in Hilborn so to avoid haveing to totally recalibrate for 2 cyls, plumbed the two spare injectors to an open line going back to the tank.
Firing order was funny, thump, thump, pause. sort of like a Harley or an old John Deere tractor.
Heavy car, two gears, (was set for 200mph or so) short track. Went 145.6 on a 145 minimum for a record (One liter record is now way over 200). We took apart, put the other two pistons in it and went 193 with three gears and were in process of changing rear to try accelerate better and get over 200 when it rained. Next year put turbo on it.
Anyway, the firing order was funny but it did not vibrate or shake and didn't break anything and it was an aluminum engine not known for strengrth (Vega)
Fun.
Jack
By removing the pistons and rods from the 2 cylinders you then make the engine EXTREMELY unbalanced as the crank passes 1/2 stroke and the engine wants to push the crankshaft out the sides of the block. This is why the inner pistons move in unison and the outer with each other. The counterweights are balanced for the pistons/rod weight but at 1/2 stroke the pistons are moving in a vertical plane and the big ends are going horizontal. not too bad if they are balance by two rods on the opposing side of the crank, but take them away and it will shake the teeth out of you head! That is why 4 bangers use a balance shaft to counter these imbalances and improve ride quality.
Robert
Interesting thing these two cylinders from one engines. Are there other people in the class that destroke and put thick sleeves to get the 1/2 displacement? If so how competitive are they?
I've had an aversion to uneven firing orders, it must be an uncomfortable sound to hear these halved engines if the firing orders are uneven probably something like a dead cylinder or a V-twin.
SchmidtMotorWorks wrote:Interesting thing these two cylinders from one engines. Are there other people in the class that destroke and put thick sleeves to get the 1/2 displacement? If so how competitive are they?
I've had an aversion to uneven firing orders, it must be an uncomfortable sound to hear these halved engines if the firing orders are uneven probably something like a dead cylinder or a V-twin.
Yes the firing order was funny, like a v twin. these days halving the displacement is easinly done by buying a high end motorcycle engine and going very fast for these small classes. There are enough other engine sizes out there to come up with something easily for any class. In my case I would have had to totally reengineer the car and really was just doing a "shake" down with the lower displacement.
I've balanced several inline 4 cranks. I've seldom ever had to drill more than 8 or 10 grams out of any end. All I've ever seen balance within .25 and most within .1. .25 is considered race ready.
The piston weights do not matter. You can zero counterweight the cranks if you would like. Sacrifice strength but you can do it and no balance issues. The main thing is the piston rod combos weigh the same. Paying someone 150 bucks or so to balance a 4cyl crank is a joke IMO. Just give them a few bucks to balance rods and pistons and save the money on the crank balance.
-Schmidt,,,You should hear the big blown nitro 4cylinder-half a top fuel hemi's (there are two of them in different classes) run balls out for 5 miles on a clear crisp cool morning, no other sound like it.
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-The Freudiger family runs a modified unblown fuel roadster on 80 to 90% nitro where they use a simple Enderle stack injected 302 Chevy (cast iron production heads-flattappet cam) but only 4 cylinders at a time and this car runs 223 or so.
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-Then there's a little bitty 3cylinder blown fuel Chevy sprint production bodied car (the little economy car and its productin based engine) that runs 156mph and that's one very impressive little motor.
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-The hotrod shop from Idaho ran a normally aspirated carbureted smallblock Chevy roadster with only 7 pistons because the engine they had was too large for the class by one hole.
-They set a record with that engine and then subsequently broke that record again several times and ended up at around 180mph.
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-I don't know much of what people would do to downsize their engines but I don't think anybody would down sleeve the block much because of the restrictions to airflow.
-it seems that most people just run with half the pistons to run the small classes.
Ouch! as coke a cola comes out of my nose, that's too funny!
Sounds like a fun bunch of racing. I really miss the technical variety that used to exist in drag racing. Mayby I will get involved in this land speed stuff.
What age do kids begin racing in land speed? I was planning to buy a jr dragster for my son but it is performance limited so I don't know how long I could keep interested in racing with performance limits. You can only have just so much fun with reaction time. Soap box derby for sure.
-at the SCTA (Southern California Timing Association) events drivers are required to have a valid state drivers license and if they are under 18 they need a signed medical and a minor (under age) release.
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-Some years ago USFRA (Utah Salt Flats Racing association) had a specific course set up for JR dragsters and go-karts for the younger kids, to try to generate some future interest into the younger generation.
-The September event is santioned by USFRA and they have several short courses, one thats a mile long to allow street legal cars to run up to 130, then they have a shorter course maybe 300ft long that is used for barstools-motorized monowheels-motorized skateboards-and other miscellanous means of motorized speeds up to about 60 MPH.
-So I'd think that USFRA would be the only place a youngster could start.
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-You could call Dan Wright (who is the USFRA tech inspector) at 801-585-7863, this is his work number at the University of Utah.
-He can usually talk to you or if he's not at the phone he'll call you back if you leave a short message of your interest in racing at Bonneville.
Ouch! as coke a cola comes out of my nose, that's too funny!
Sounds like a fun bunch of racing. I really miss the technical variety that used to exist in drag racing. Mayby I will get involved in this land speed stuff.
What age do kids begin racing in land speed? I was planning to buy a jr dragster for my son but it is performance limited so I don't know how long I could keep interested in racing with performance limits. You can only have just so much fun with reaction time. Soap box derby for sure.
I started at Bonneville in 1979. haven't been every year but maybe 15times. Is a 2200mile one way tow so has to be important. If you are not a gearhead, comments of "watching paint dry and grass grow" are heard. If you are, there is nothing like it. Though there are pros and corporate money is creeping back in, many are amatuers and innovation is king, as this thread has shown (7/8th of a small block!) Newer stuff like computers, traction control cause controversy and safety rules by some standards are still a bit behind times I think but they are improving and is rare to have a problem. Bill will agree I am sure- The Salt gets in your blood. I love it out there, the cars and the desert. Going this year couple days to watch, hopefully next with new car.
Getting back to the original question: 10 grams, at the piston, would translate to a crank load of about 150 pounds at 10k rpm and less than 40 at 5k. Pretty small compared to other loads.
Trivia: Had an engineering classmate, in the early fifties, who successfully cut a Chevy six in half. Was considering putting it in his MG, but never did.
