Manco 386B-17 Issue

[Missile]

the seven inch driven is only providing you with a tad more wheeltorque..
that's okay no need to purchase anything but a driven spring IMHO.

Since yours look rather busted to me (coating cracked.. steel rusted ...)
Full Driven maintenance is due I'd say..
cleaning the sheaves to babybutt smoothness, new spring, and you'll be good.

Now initial issue:
chances are the jackshaft bearings are worn out..
remove the belt and wiggle on your driven unit..
if there is any play, you can be sure it's causing vibrations when running.
Also make sure the Jackshaft is 100% parallel to the PTO of your engine,

so also remove the driver pulley from the engine for a moment.
Get a tailors tape measure out and wrap it around both shafts as if it were a drive belt
twice: first snugly at the PTO output bearing. (take exact note!)
then at the very end of the pto shaft (again take exact note!)
and if the two numbers are not identical,
chances are the two shafts are not parallel.

Once the shafts are parallel with the jackshaft bearings in good condition and a freshly maintained TC,
there shouldn't be no excessive vibration (no other than engine vibration actually)

'sid

I'm glad I removed the driven pulley, the jackshaft bearings are bad. The front wheel bearings are also bad. All on order. Thanks for the advice.

 

[Denny]

Sounds like you finally got it under control. Good deal.


Denny

 

[Missile]

I installed the new jackshaft bearings and noticed that the outer diameter of the bearing has some play inside the jackshaft. I tried the old bearings and there's play as well. Not sure if the jackshaft tube is worn out. Both ends of the jackshaft has some play around the outer diameter of the bearings, it's a 5/8 x 1 3/8 bearing. Not sure how to fix this without replacing the jackshaft tube? Any ideas?

I have a 60 tooth sprocket that I can put on to see if this helps with the vibration. It has a 52 tooth sprocket on it now (stock should be 54 tooth).

 

[Guapo613]

22x11-8 with a 52-9 tooth combo is pretty tall gearing. You either need to increase the 52 or reduce the tires size. It's shuttering because of the tall gearing, I'm pretty sure once your moving it's no problem but punching it from a dead stop causes the belt to grip/slip/grip/slip/grip/slip.

 

[Missile]

22x11-8 with a 52-9 tooth combo is pretty tall gearing. You either need to increase the 52 or reduce the tires size. It's shuttering because of the tall gearing, I'm pretty sure once your moving it's no problem but punching it from a dead stop causes the belt to grip/slip/grip/slip/grip/slip.

I put the 60 tooth sprocket on and the vibration is all about gone
I did notice that the disk brakes were binging a bit, fix that as well but I'm thinking it's the sprocket that did it. Thanks for all the help guys!

Now I'm thinking of adding semi-independent suspension to the rear using a single 1" heim joint.

 

[Missile]

Received my order for some mods. 18lbs valve springs (gov removed), main jet (no size listed on jet but made for 212cc), header and pit bike muffler, and K&N style air intake.

I noticed the intake port on the head is much larger than the spacer between the carb and head. This must be restricting the air flow? Is it advisable to Dremel out the spacer?

 

[mckutzy]

Do you have a billet con rod???
If NO, Id suggest do not install the springs and leave stock till then.... doing so will most likely have rod dissection and hole in block....
The stock spring will allow the motor to have valve float at an RPM just under the limit for in which dissection will occur..

 

[Missile]

If I were to go with a bigger cam, I would add a billet connecting rod and flywheel. The valve springs are to lesson valve floating at higher RPMs due to the governor being removed. The stock connecting rod is fine with these mods, not a great HP/torque gain but anything is possible. I can accept the risk.

 

[JTSpeedDemon]

If I were to go with a bigger cam, I would add a billet connecting rod and flywheel. The valve springs are to lesson valve floating at higher RPMs due to the governor being removed. The stock connecting rod is fine with these mods, not a great HP/torque gain but anything is possible. I can accept the risk.

Well, I will second Mckutzy that that is a bad idea.
It is your choice, but just know that you will probably end up with destroyed engine internals to the point of no repair, and you will probably end up with extra crankcase ventilation(a hole in the engine block)!!

 

[mckutzy]

You want to induct that with these engines....That is the gov, with out the mechanical one....valve float.

Im guessing you have V6/8 +cylinders engine experience..... and often this is what they say about those type of motors(car engines)...In the small engine world of these small block clones it doesnt translate well to the small "versions" and this is one particular aspect of that...

New rod new springs, old rod old springs(Stock that is)...

 

[JTSpeedDemon]

You want to induct that with these engines....That is the gov, with out the mechanical one....valve float.

Im guessing you have V6/8 +cylinders engine experience..... and often this is what they say about those type of motors(car engines)...In the small engine world of these small block clones it doesnt translate well to the small "versions" and this is one particular aspect of that...

New rod new springs, old rod old springs(Stock that is)...

And of course you could also do new rod old springs.
But yes, when a rod blows on a go kart, it is almost infinitely more dangerous than in a car, because you don't have a firewall or engine accessories in the way of shrapnel.
So it's not inconceivable to end up with a chunk of connecting rod in your back since the engine is right behind you.
Imagine filing that insurance claim: "I was riding my modified go kart when the engine exploded, so I ended up with metal shrapnel in my back."
I would imagine that would drive up the insurance premium.
So please, leave the valve springs stock until you upgrade the con rod. Years of experience and a few catastrophic failures here and there will back us up.
Besides, if you plan to do mostly off roading and don't expect to see high rpms that much, you won't really notice the extra rpms!
Please, we don't want you to get hurt.

 

[mckutzy]

Well ya the danger is exponentially greater in a car comparatively, period...
Im just saying similar thought of theory in internal combustion engines dont scale to these engines....
I think FHB had demonstrated an item from his turbo truck to his karting experiances, aswell as bob58o in a few similar circumstances...

 

[Missile]

I appreciate the concern. Per the stiffer springs white paper "A billet connecting rod and flywheel are recommended, but not required." (For my application)

I've experienced bent valves due to valve float, but not dissection. Yes, I'm a gear head, last mod was supercharging the car. I'm no expert by any mean's, it's just based off my experiences. There's always a risk when you mod weather $$$ or whatever.

It's kinda funny, 4 years ago I had a 38% chance of living and I'm still here. I understand that you feel I'm taking an unnecessary risk, I don't see it that way.

I'm getting ready to mount the muffler to the frame. Planning on shaping a piece of angle iron. I'm just glad to have been able to build a small shop and work with my hands again to be honest.

 

[landuse]

I would also advise against going stiffer springs with the stock rod, but as you say, it is up to you and it is your engine to do as you like. We have just seen too many rods going through the block going the route you are going