Opinions sought, mechanical question

[SPYDERLK]

daTeacha would have to make the call.

In my case I would make the call based on the perceived abilities of the girl, or woman? You can usually tell what kind of lights are on. If she has the ability to understand and reason out the choices I would steer her toward doing that - not just confining herself to a rigid limitation for putting in an identical part. Informed flexibility, weighing cost/benefit, choices and their realistic consequences is a great strength. It seems she or someone helping her has already put the pistons in one way and decided the results were bad. Somebody is thinking, but which way was that? I havnt yet had a clear indication. I just know that both heavies on either the ends or the middle is bad, and a heavy 2 throws away from another heavy is not good. There is knowledge to be conveyed here. If she is apt find her some lucid books. If she experiments give special attention to nuances. If not, teach her procedure.
Larry

 

[daTeacha]

Okay, it's been a while since I've had a chance to speak here. Some clarification and updating is needed.

First of all, I'm involved in this project only because the girl (17) used my balance to weigh the pistons. The girl does not own the tractor and the parts are being paid for by the guy who does own it. I am not in a position to offer any other assistance outside of verbal suggestions, which are added to the advice of several others.

The pistons are aluminum with steel rings. A new one with rings weighs about 12 ounces more than an old one with rings despite being about an inch shorter in the skirt area. The pistons were purchased specifically for the tractor in question and are intended to fit and work in it. They are costly and the owner does not want to invest in two more.

With wrist pins in place, the new one is 9 ounces more than the old one since the wrist pins are smaller in the new one. Installing the needed bushing to make it fit the stock con rod might bring the weight difference up to 15 or 16 oz. per piston.

The 1 and 4 piston run in tandem, as do the 2 and 3. This somehow makes more torque than the way modern 4 bangers run, although I would like to know why.

The tractor had been previously assembled with the heavy pistons at 1 and 3, and it shook a lot. The consensus of opinion between the Oliver hot rodder and the owner is that it will be much better if the heavy ones are running in tandem.

The tractor is now assembled with the new pistons in cylinders 2 and 3 rather than 1 and 4, although I don't know why that decision was made.

Again, the tractor is destined to be just a show queen, not a working tractor, so the idea is to get it to run enough to drive onto and off a trailer and maybe in a parade now and then. It will never do any serious work in the future.

I tend to think like most of you guys -- the pistons should be pretty closely matched in all respects for best results. I told the girl today that the general opinion here was not in line with the way things were being done, but that's when she told me it was already together with the heavy pistons in 2 and 3.

I'll keep you posted as I hear more.

 

[SPYDERLK]

Rich, thank you for the very good description. I was afraid of that, yet would have been surprised to hear differently. The 1 and 3 installation set up the worst rocking couple you can make out of that engine - the heavy pistons travelling opposite one another and as far apart as possible. The 2 and 3 installation demonstrates the worst imbalance you can get and compounds it by throwing it all onto the center main bearing, calling its survival into question. The owner is taking responsibility here and is making his decisions with consistant randomity. Try to save the student.
Good luck, Larry

 

[cp1969]

The 1 and 4 piston run in tandem, as do the 2 and 3. This somehow makes more torque than the way modern 4 bangers run, although I would like to know why.

Do you mean they fire in tandem or just travel up and down together? Because all inline fours that I've ever seen have #1 &4 travelling up and down together. If they fire together, this thing would have to sound like a two cylinder John Deere. It could make more torque if they fire together and have an enormous flywheel. The 11" stroke still has be wondering...also, I come up with 864 cubic inch displacement with those numbers. That is a huge 4 banger--by far the largest I've heard of in a tractor. I remember reading that inline 4's bigger than 2.4 liters need a balance shaft...this guy is 11.7 liters over that limit.

 

[dancer]

I just wonder what you guys think about this one. One of my students brought in two pistons from a tractor she is restoring for FFA. The engine is a gasser, tops out about 1600 rpm. The pistons are 5 inches in diameter on a 4 cylinder engine. She has two new ones and two old ones. The new ones are about 9 ounces heavier than the old ones -- around 2.1 kg vs. about 3 kg. ...

I read the entire thread quickly to find what I thought I was missing from the original post -- and I didn't find it. Is the difference in piston weight 9 ounces, or nine-tenths of a kilogram (0.9 kg)? When a kilogram is 2.2 pounds, that's a large difference.

 

[rback33]

I read the entire thread quickly to find what I thought I was missing from the original post -- and I didn't find it. Is the difference in piston weight 9 ounces, or nine-tenths of a kilogram (0.9 kg)? When a kilogram is 2.2 pounds, that's a large difference.

I must say that I was a bit confused as well as to the true diffence in Mass. Too many units of measure were thrown out there....

 

[SPYDERLK]

Let me see if I understand this.
You have a 4 cylinder engine.
Two pistons operate in tandem,
and the other two pistons operate in tandem.
Meaning two go up at the same time and down at the same time.

So why not put a heavy one and a light one together.
Wouldn't this keep everything balanced.

Note: I've never seen a 4 cylinder engine where the pistons
acted in tandem like a 2 cylinder engine. V-8 and V-6 engines yes.

Pooh Bear

This is the 1st time in the thread I saw the tandem issue. It sounded like a conventional 4cyl as introduced.

Rich, do 1,2 go up while 3,4 go down? If so, the 2,3 combination for the heavy pistons is the best choice. The extra torque, if not just a figment, must come from a more optimum intake or exhaust staging arrangement.
Larry

 

[patrick_g]

da teacha

Well here is a different angle. Put it together with the parts the owner is willing to buy and if it shakes like Elvis you can explain to the girl that sometimes folks make bad decisions in repairing equipment and this was one of those times. An opportunity to teach that if it is worth doing it is worth doing right.

It shows how spending only part of what is needed is bad economics and not wasting time and $ on the project might have been better if it were not going to be done right. Sometimes a job is better off not being done if it can't be done right.

Pat

 

[daTeacha]

It is my understanding -- from what I've been told -- that one and four go up and down together, but it was never clarified as to whether they were on the same stroke. I have to presume they are not, with one on power while the other is on intake. Similar with 2 and 3. I haven't seen the engine personally.

The difference in ounces is correct -- a new piston with rings in place weighs 12 ounces more than an old one with rings in place. With the wrist pins in place the difference drops to 9 ounces because the new one takes a smaller wrist pin than the old one. A bushing will need to be added to the new one to fit the stock connecting rod, raising the weight difference up from the 9 to at least 12, maybe more.

And yes, from what I've been told, the stroke is around 11 inches with a 5 inch bore. The tractor is an Oliver 99 from 1953. I haven't looked at tractordata.com to verify any of this, I'm just passing stuff along for you guys to discuss. I'll check now and see if it's there.

Okay, according to tractordata.com, the gas engine 99 displaces 443 cubic inches and produces 54 engine hp with 41 hp at the drawbar. It weighs 7300 lb. That should qualify as a large 4 cylinder. That displacement calculates out to around a 5.6 inch stroke if I did the math right. That seems more realistic than 11.

So, when the engine is running and pistons 2 and 3 are going down, there is at least 24 ounces more weight going down in the center of the engine than there is going up at the ends regardless of which one is on power stroke. The plan when she left here Friday was to put the heavy pistons in cylinders 1 and 4. I don't know why they changed it.

 

[HGM]

Well, it sounds like she is more of the guinie pig of the owner... In which case, its not fair for her to be graded on the project, but thats a different topic.. I'm very curious how it will come out though.. My gut feeling is that it would work best to have the heavies in oposing strokes, like 1&3 but obviously that didnt work ... If it were to have a heavy piston on comp stroke while the other heavy was on intake, it seems they would balance out... But, when the second heavy comes down on power stroke, the other is exhausting with little resistance... With them on the comon through, I believe there will be alot more stress on the crank and bearings because of the added weight causing a wringing motion of the crank.. I'm not an engineer, but I have a hard time believing it wont vibrate with any combination....

I do like the recomendation to explain to her that it isnt her fault and that this will prove why it should have been done right(like she wanted to, hopefully) in the first place..