16hp engine w/ tranny ideas

[jamyers]

Heres the loose plan...a Briggs 16hp opposed twin engine with a pulley on the crank. A '76 Saginaw 4-speed tranny (relatively lightweight, and 1st gear is roughly 3:1). Pulley/belt drive to the tranny with a tensioning clutch (either a pedal or hand lever, haven't decided yet) to a pulley on the trans input shaft (pulley bolted to old clutch disc hub). Very end of trans input shaft supported by ball bearing. On the output side, a sprocket welded to a cut-down driveshaft yoke, then chain to the rear axle.

That's with the crankshaft and tranny mounted sideways, the tranny right behind the engine. The shift linkage becomes the hard / complicated part here.

Or I could turn the engine / tranny 90* so the crank / tranny run fore/aft , use a stock car shifter, and some sort of right angle drive to the axle - which becomes the hard part here.

Thoughts?

 

[rwd4evr]

i would try to put a support bearing inside (close to the trans) and on the crank pilot end, transmissions aren't designer to take any side loading. go with the chain setup and use shifter or some other type of heavy duty push pull cables with the factory shifter.

 

[jamyers]

Hmm, push/pull cables on the old shifter sounds like a good deal. I'll see if there's room on the input shaft for a second bearing, might have to cut the snout off the throw-out bearing housing on the tranny front to make room..

I'm also contemplating making it front-engine if I can snag a REALLY small/light car axle/differential at the wrecking yard...

 

[fowler]

Could u mount the tranny and engine in line

Run a cent clutch with a chain
Then find a similar sprocket and mount it to the input shaft on the box

Then use the old double link chain to join the two sprockets

As long as u can align the two components correctly

 

[Acavet]

Going to loose a lot of H/P turning a trans that size, might want to consider something even smaller like a VW trans Then you have all the benefits of a trans and differential all in one. Just make sure to support the input shaft.

 

[jamyers]

I'm not sure it'll take much to turn this, it's pretty light and turns pretty easily by hand. Plus, I'm going to swap the 80-90 gear lube for lighter oil or ATF even, since it'll be seeing way less torque and time in use.

If I had or could score a VW transaxle though....

 

[cumminsbayou4x4]

so is it a car transmission? i have a old murray gt 18 that has a vertical shaft 18 opposed twin but a horizontal shaft transmission. they also had gt 16 with a 16hp oppy. The transmission is really heavy and i don't think it will ever break it has a 5lug hubs to. If i was you id try to get one and just use a belt or centrifugal clutch and a sprocket on the transmission

 

[jamyers]

Yep, it's out of a Vega, iirc. The problem with mower trannys is that they're not made for shifting in the go - at least I haven't found one in all my local and Internet searching

 

[cumminsbayou4x4]

with the centrifugal clutch you could

 

[jamyers]

with the centrifugal clutch you could

From what I gather at the racing mower forums you *can*, but it's not recommended.

The real issue you are going to run into is reliablilty due to all the shifting you are planning on doing. Up shifting is fairly easy burp the throttle and shift down sifting is what eats a trans up and breaks parts, becaus you cannot relieve enough load to down shift its not a syncro setup your forcing keys into moving parts and down shifting is very hard on this transmissions.

Besides, this tranny is just sitting there...

 

[Doc Sprocket]

Yeah- All the research I have done on mower trannies suggests that shift-on-the-fly, ain't. In stock configuration, they will tend to tolerate it. But once you start using it for an unintended purpose, all bets are off.

Once you've had your hands into a couple of mower trannies, it becomes very clear why you don't want to be shifting on the fly. It matters not whether you are belt-clutching or using a centrifugal. They simply do not have the architecture to support this.

Jammy, I am REALLY intrigued as to what you're cooking up. Homebrew tractor, maybe?

EDIT- With the current tranny and engine mount plans, would the factory shifter be within the operator's reach?

 

[jamyers]

...
Jammy, I am REALLY intrigued as to what you're cooking up. Homebrew tractor, maybe?

EDIT- With the current tranny and engine mount plans, would the factory shifter be within the operator's reach?

Oh, yeah the shifter is going to be within the operators reach, I want to row some gears!

Well...it's mostly in my head, but I'm pondering either:

1. A scratch-built kart (small car?) with the engine up front (crank fore-n-aft) and offset to one side, this tranny behind it and offset to the other with the belt-tensioner "clutch" between them and pedal-operated, with a driveshaft (tractor pto) going back to a differential out of something tiny like a Pinto, Vega, MGB, whatever I can scab from the yard. A car axle is heavy, but would have a diff, fantastic brakes, and could easily be suspended - and would prolly be less unsprung weight than an engine w/ tranny sitting above the rear axle on a spring-arm. Here the stock car shifter could be used and located in the middle of the kart just to the driver's right.

2. Modding the Yerf-Dog some more to put this engine on it (crank side-to-side) with the transmission close in front or behind the engine, same belt / clutch idea, with a sprocket welded to a trans output yoke chained to the kart live axle for the final drive. Here I'd use the stock shifter bolted to the kart floor and push/pull cables back to the gearbox. Probably want to move the live axle as far to the rear as possible and do some beefing up of everything behind the swingarm pivots and shocks, etc. The front end of the Yerf is going to get some work done to it in the near future regardless of what happens to the power plant - it's not bad, but could be better.

Edit: whatever it is it needs to be able to go off-road and carry a passenger.

 

[Doc Sprocket]

Neat ideas. I asked about shifter location because of your own comments. IMO, KISS. If you can reach it, don't complicate it. Even if you have to re-learn the shift pattern at 90* to what you're used to.

 

[OzFab]

The difference between a mower trans & a modern automotive trans is the mower trans is a clash style & the automotive box is a synchro style box.

A synchromesh style transmission uses an intermediate (for lack of a better word) gear to help align the gear with the engagement collar, making changes a lot smoother & easier.

A clash box simply has two gears that mash together. Way back when, before the invention of synchro's, clash boxes were used in cars & trucks so, it is possible to use a mower box on a go kart but, there are major disadvantages:
1. The constant clashing & mashing of gears, obviously, will drastically shorten the life of the gears
2. "shifting on-the-fly" becomes more like "shifting on-the-walk" (what do you call a fly with no wings? A walk ), the box will decide when it wants to engage, not when you want it too. This results in loss of momentum which, in turn, means loss of power/speed & forces the next gear to work harder.

Just my 2 cents worth

 

[fowler]

Not to be arrogant but...
An auto trans is an arrangement of clutches and plantary gear sets

And a synco is two or 3 intermeshing cones that act to bring both shafts to the same speed
So u can slip in the collar


Is a mower trans a constant mesh box or a sliding gear type
Sliding gears won't handle any differance between the two gears while shifting

Constant mesh like the old crash boxes can handle a little but won't take it for to long

 

[jamyers]

Most Mower boxes are constant-mesh with 2 or 4 sliding keys that lock one gear at a time to the shaft. Problem is, the gears are right against each other and there is nothing to help smoothly engage a gear when shifting, which is why they don't shift very well (if at all) when moving - it *can* be done, but it's tempting fate and not easy.

The other tranny I have laying around is an old Ford "2.77" manual, which is very light/small but doesn't have synchros on 1st gear- a pain to drive even in a car which is why it's on the shop floor.

 

[Maine Mud Mower]

2 cents from the mud mower guy
In a lawn tractor they are ment to do one set of actions from factory. Start in 1st shift up on the fly as needed hit clutch/brake you stop start over again. In off roading a mower you can retard the brake ingagement this way So that for the first inch of two of brake/clutch you only actuate the clutch. This alows you to down shift well not ingaging the brake and reliving the torque on the tranny. It comes at a cost thoe of not having full braking capability. You can still stop but you got to plan it a little bettter and have to run your brakes fully tensioned.

 

[devino246]

The other tranny I have laying around is an old Ford "2.77" manual, which is very light/small but doesn't have synchros on 1st gear- a pain to drive even in a car which is why it's on the shop floor.

The car in my avatar (now restored) has an unsynchronized first gear. It's really not much of a problem.

 

[Doc Sprocket]

Yeah- once you're used to it and know what to expect, it's fine.

 

[jamyers]

I drove the non-synchro 2.77 tranny in my '62 Ranchero for years, and you're right, you can get used to it - but it's SO much easier being able to slide into 1st while still moving without the occasional gri-i-i-i-i-i-i-i-nd.