Engine bucking?

[blaino]

Newbie here!

Just finished my first build - thing is pretty sweet. Strapped an old China Lady to my cruiser and the thing flies. Only a couple things I wanted some advice on. It bucks pretty significantly at very low speeds. I know at low revs engines tend to do that, but this seems a little different. I'm having trouble telling if it's the motor or maybe something revolving around the chain because it jumps so much when it's bucking?

Also, the motor slightly tilts to the left, almost as if the chain is trying to pull it down.

Anything to be concerned about?

 

[Mr. Minecraft]

Welcome to the forum Blaino!

As far as the bucking goes, the HT's have a manual clutch, when engaged, directly transfers the engine's power to the back wheel without any dampening. The bucking you are feeling is the piston moving up in the cylinder, causing compression which gives resistance. Then the engine fires, which speeds it up slightly, then compresses again, giving resistance. This happens thousands of times per minute at higher speeds, so you never feel it. However at lower RPM's, you can feel everything the engine is doing. My theory about the chain bucking is that it might be a tad too loose, and the engine running that slow might be making it jump around a lot. I always have around 3/8-1/2 an inch of slack in the chain. If you don't think this is the problem, let us know and well try to diagnose the issue as best we can.

In regards to the engine tilting, try to make it as straight as possible for the sake of the chain's alignment. You will save a lot of trouble and money by having the chain properly aligned from the get-go. Now if the chain is not making popping/cracking sounds when the bike is rolling and if the chain is not struggling to stay on either sprocket, then the degree of tilt is very minimal and should not be worried about.

Pretty much ride the bike like normal, but keep a close eye on it. This should be done with any new build. Take it out, ride it, and put it through its paces. After the ride is over, check all components of the engine as well as the bike (these engines vibrate a lot and can cause stuff to loosen up). Once you have made sure everything is ok, you can ride for longer periods without having to check on the bike and engine. Pretty soon you will be going thousands of miles without even thinking of your bike

Again, welcome to the forum, and ride safe!
-Chris N.

 

[blaino]

Awesome, thank you!

 

[maniac57]

I think Mr. Minecraft said it all, except I would suggest you make sure the motor is straight and true in the frame, and make sure it STAYS that way. I can't tell you how many bikes I've had come in with the engine hanging off like you describe, leading to chain, mount and even frame failures. Keeping the motor tightly in place will prevent a lot of issues in the future.


BTW: I'm well past the stage where thing keep loosening yet I still check the bike over EVERY SINGLE TIME I ride it.
Better safe than pedaling(or pushing)

 

[Mr. Minecraft]

Make sure it STAYS that way. I can't tell you how many bikes I've had come in with the engine hanging off like you describe, leading to chain, mount and even frame failures. Keeping the motor tightly in place will prevent a lot of issues in the future.

I'm well past the stage where thing keep loosening yet I still check the bike over EVERY SINGLE TIME I ride it.
Better safe than pedaling(or pushing)

Exactly.

 

[hollywood528]

To fix the engine tilting, I ran a longer bolt through the clutch cover rear most hole. It just so happened to line up with my seat post bar on my frame. I cut the bolt so it just came in contact with the frame when tight. After doing this, I haven't had my motor tilt since.
I'll try to get a pic so you can get a better idea of exactly what I'm talking about.

 

[blaino]

To fix the engine tilting, I ran a longer bolt through the clutch cover rear most hole. It just so happened to line up with my seat post bar on my frame. I cut the bolt so it just came in contact with the frame when tight. After doing this, I haven't had my motor tilt since.
I'll try to get a pic so you can get a better idea of exactly what I'm talking about.

Awesome, thanks.

 

[Mr. Minecraft]

To fix the engine tilting, I ran a longer bolt through the clutch cover rear most hole. It just so happened to line up with my seat post bar on my frame. I cut the bolt so it just came in contact with the frame when tight. After doing this, I haven't had my motor tilt since.
I'll try to get a pic so you can get a better idea of exactly what I'm talking about.

I see what you mean, its acting as a stopper to keep the motor from moving any more. it seems to me that the vibrations and use of the bike would cause this to ruin the surface its in contact with. I'm not saying its a bad idea, but I wouldn't do it to my bike without some sort of medium between the bolt and frame (maybe a piece of innertube?).

 

[blaino]

The engine tilts literally 3-5 degrees or so to the
left. You think that's cause for concern?

 

[hollywood528]

Ya, it may scratch it. It honestly hasn't done much damage so far. But I really don't mind, I'm running cheap Kent mountain bike I picked up for twenty bucks.
But ya, a piece of intertube would definitely help. Even maybe a clamp that goes around the seat tube so the bolt comes in contact with that.
On my chopper build I'm welding motor mounts so I don't have to worry about this.

 

[Groove]

The engine tilts literally 3-5 degrees or so to the
left. You think that's cause for concern?

The old How's it Hangin' question..

There's a thread out there (I know because I asked the same question), where people debate this topic. The general concensus is that you should mount the engine centered in the frame, nice and snug, and preferably without using rubber vibration dampeners because they transfer too much vibration to the mount studs. When resonance frequency is inevitably achieved....snap!

Having said that, I mounted my first engine using rubber dampeners and leaning about 3 degrees to the left (inadvertently) and it's great at 500+ miles.. Just my 2 cents.

 

[Risingsunn]

Also on a new engine, new mount, check and tighten all bolts every ride for the first few rides. Things tend to vibrate loose easily on these rattletraps.

 

[2door]

Also on a new engine, new mount, check and tighten all bolts every ride for the first few rides. Things tend to vibrate loose easily on these rattletraps.

I have to disagree with the wording in this advice because too many people read the word "tighten" and they believe they should get a turn on the fasteners "every time they ride". Doing this is a sure way to twist off a stud or strip the threads in nuts.

A torque wrench should be a required tool to own and it should be used, especially on these bikes. Set the torque value and tighten the fasteners to that value, then CHECK your fasteners but do not "tighten" them. If they have loosened the torque wrench will bring them back to the desired value (tightness) but if used correctly will warn you not to exceed that setting.

Chinese quality is all too often blamed for fastener failure when in fact any fastener can fail if over tightened. "Tightening" your fasteners after each ride will assure that you'll eventually break something. This applies to engine mounts, head bolts, intake and exhaust, even axle nuts and handlebar adjustments.

Don't "tighten" but only check the tightness, and use a torque wrench.

Tom

 

[crassius]

with a 10mm wrench about 4 inches long, I use the 2-finger rule - if it feels tight when pulling with 2 fingers, it's about right

 

[2door]

with a 10mm wrench about 4 inches long, I use the 2-finger rule - if it feels tight when pulling with 2 fingers, it's about right

Experience counts for a lot. Getting a "feel" for how tight is tight comes with doing it over and over. There are many very good mechanics out there who do not use a torque wrench and never have any problems. They are the exception.

This forum is designed to 'help' the inexperienced construct a reliable and useful motorized bicycle. When the advice they read tells them to "tighten" their fasteners they take that as to mean they should "tighten" nuts and bolts regardless of how tight they are. By tightening, they believe they should see the wrench turn the fastener a little each time they try it.
That's where the trouble begins.

Cassius is undoubtedly an experienced wrench turner and understands the limits but all too often new and inexperienced builders do not.
There are hundreds of threads and posts here about failed fasteners and stripped threads and the majority of them could have been avoided had the builder not over tightened them.

Tom

 

[maniac57]

Experience counts for a lot. Getting a "feel" for how tight is tight comes with doing it over and over. There are many very good mechanics out there who do not use a torque wrench and never have any problems. They are the exception.

This forum is designed to 'help' the inexperienced construct a reliable and useful motorized bicycle. When the advice they read tells them to "tighten" their fasteners they take that as to mean they should "tighten" nuts and bolts regardless of how tight they are. By tightening, they believe they should see the wrench turn the fastener a little each time they try it.
That's where the trouble begins.

Cassius is undoubtedly an experienced wrench turner and understands the limits but all too often new and inexperienced builders do not.
There are hundreds of threads and posts here about failed fasteners and stripped threads and the majority of them could have been avoided had the builder not over tightened them.

Tom

This is great advice. I'm one of those that does it by feel and I learned after breaking many, many fasteners. A torque wrench is a smart investment for any new builder to consider.
Right after they replace the kit chain...

 

[577-Jersey]

I agree,,
Dont be afraid to tighten them motor mounts down,,you will feel when everything bottoms out after the lock washer,clamp,frame tube,and motor become one.Suck it all together nice and tight using the torque wrench like stated making sure everything is square/flush.You want that motor rock solid.Believe me they run excellent when built right.

A good little experiment to do is get a couple 6mm nuts and bolts,,put them in a vise and tighten them up until they start twisting and break,,you will get a better feel for it after you break a few...lol

Good times

 

[Reggie boy]

Can anyone tell me how to resolve an engine bucking issue on my new zeda 100 firestorm with sick bike parts shift kit?