Spinning Crank By Hand

Francois Labat /

Hey yall,

Lot of posts lately, making a push to finish this damn moped.

I put the bottom end together, froze crank, baked the case halves.

Once the case and crank was bolted together, I could spin the crank by hand, but felt tough.

Once I put the cylinder on, pretty much impossible for me to spin the motor by hand using the crank. Is there an interference?

All I can think of is that the seals are tight on the crank, and that the cylinder adds more friction. I lubed the cylinder. Should I take this all apart again...?

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Cheers

Re: Spinning Crank By Hand

Bill Mazzacane /

> Francois Labat Wrote:

> -------------------------------------------------------

> Once the case and crank was bolted together, I could spin the crank by

> hand, but felt tough.

There should be some side play on the crank, after the case is assembled.

It is common for a crankshaft to be stuck, or bound, and need to be centered inside the crankcase after assembly. Usually a wack with a brass hammer on each side of the crank will loosen the crank and allow it to rotate freely.

I have a special tool for this to support the crank webs at bdc to prevent tweaking the crank, but if you don't have special tools you can drive 1 or 2 wedges into the crank at BDC to prevent tweaking the crank when you tap the crank with a brass hammer.

Did you oil or grease the main seals? Main seals require lubrication before an engine is started. I like using a hi quality silicone fork seal grease, but anything other than wheel bearing grease will work.

If you pack the seal with too much grease, it will cause an air-leak at the main seal.

If none of these ideas work, you may consider disassembly and inspecting the main bearings, they might not be seated properly in the crankcase half.

Did you inspect the ring end gaps?

The majority of drag caused by the rings occur at the ring end gaps. So I am in the habit of dragging a fine file lightly over the ring ends to lightly round the corners before assembly.

I prefer to assemble a top end with the ring lands and cylinder lubed with oil before sliding the cylinder on. A well lubed top end on assembly prevents a lot of cylinder wear in the first few seconds the engine runs. If an engine isn't adequately lubed, the hone pattern will quickly wear off.

Bill M.

Re: Spinning Crank By Hand

Always tap them back and forth a bit to loosen up the bearings that have a side load on them now being pressed into the cases, even if you froze it. Without seals the crank should spin completely free.

Re: Spinning Crank By Hand

Jonathan Feldman /

Sorry to be that guy but ya probably fucked something up.

Moby tolerances are lackluster at best. Getting moby crank bearings to sit correctly in the case is definitely the easier of the mopeds I've done. That shit should have close to no resistance spinning with seals out. With seals in, the resistance will increase but only slightlyyyyyy.

Things to check...

1. Make sure crank is centered in cases? I used to get mega OCD n use feeler gauges on both sides of the crank to make it perfectly centered. Heat that shit up once its bolted together with a torch and whack the crank back n forth with a rubber mallet till till you get the correct crank position. Nowadays I don't feeler gauge it. As long as it's vaguely centered you're good. The small end needle bearing is real good at taking up any slack .. if the crank isn't perfectly centered that is.

2. The crank bearings only go on one way. One side of the crank bearings is beveled n ones machined flat. Moby is the only moped that needs the bearings facing a certain direction. I'm 99% sure the beveled side goes inwards on the crank. Don't quote me.. I haven't done crank bearings in a good year or so. But they definitely only go one way. Double check the bevel side goes inward haha. If you fuck up the crank bearings that shit will bind up BAD. Personal experience haaaa

3. This is opinion but I'm REAL big on installing bearings on crank first THEN cases on. Some do it the other way.. but i never had any luck doin it that way.

I've definitely assembled Moby bottom ends incorrectly. Once again, that shit should be free spinning as fuck without the seals in. One time I fucked up and didn't get the bearings to seat correctly and I proceeded to burn out one crank bearing in like less than 50 miles. Cases even had overheating marks on the inside. Yikes

Re: Spinning Crank By Hand

Francois Labat /

Thanks everybody!

I did install the bearings with the bevel pointed to the inside of the crank (correct).

I was a little unclear in my description, I froze the crank and dropped the bearings in, then tapped them on to make sure they were on.

Then a week later I froze the assembly and mated the cases with heat.

The main consensus is that the crank might be binding somehow.

I will loosen the bolts and heat up the cases (gently), use a rubber mallet to tap. I do thin that there is one gap larger than the other when I look at crank and case.

How could the crank have side to side play if the bearings have a press fit on the case??

I have to ad a leaf to my truck springs today but might get to experiment tonight. I hope so.

Thanks guys

Re: Spinning Crank By Hand

Francois Labat /

> Bill Mazzacane Wrote:

> -------------------------------------------------------

> > Francois Labat Wrote:

>

> > -------------------------------------------------------

>

> > Once the case and crank was bolted together, I could spin the crank by

>

> > hand, but felt tough.

>

> There should be some side play on the crank, after the case is

> assembled.

>

> It is common for a crankshaft to be stuck, or bound, and need to be

> centered inside the crankcase after assembly. Usually a wack with a

> brass hammer on each side of the crank will loosen the crank and allow

> it to rotate freely.

>

> I have a special tool for this to support the crank webs at bdc to

> prevent tweaking the crank, but if you don't have special tools you can

> drive 1 or 2 wedges into the crank at BDC to prevent tweaking the crank

> when you tap the crank with a brass hammer.

>

> Did you oil or grease the main seals? Main seals require lubrication

> before an engine is started. I like using a hi quality silicone fork

> seal grease, but anything other than wheel bearing grease will work.

>

> If you pack the seal with too much grease, it will cause an air-leak at

> the main seal.

>

> If none of these ideas work, you may consider disassembly and inspecting

> the main bearings, they might not be seated properly in the crankcase

> half.

>

> Did you inspect the ring end gaps?

>

> The majority of drag caused by the rings occur at the ring end gaps. So

> I am in the habit of dragging a fine file lightly over the ring ends to

> lightly round the corners before assembly.

>

> I prefer to assemble a top end with the ring lands and cylinder lubed

> with oil before sliding the cylinder on. A well lubed top end on

> assembly prevents a lot of cylinder wear in the first few seconds the

> engine runs. If an engine isn't adequately lubed, the hone pattern will

> quickly wear off.

>

> Bill M.

Thanks , reassuring that I can maybe get it set right by a little hammerin’.

There technically isn’t axial play in the crank unless you heat up the cases ? I don’t see how the crank could have movement left and right if it’s a press fit (interference fit on the bearings). I’ll give it a tap with heat later. Leave the case bolts on. I for sure can see that there is slightly more gab from crank to case on one side. Small but that could be it

Wish I could mess with it rn but gotta go mess with my truck.

Re: Spinning Crank By Hand

I had this happen with a 103. The crank was centered but there was still a tight spot so I put the whole thing back in the oven and used a temp gun to make sure everything was hot enough then tapped lightly around the seals and the crank on both sides till it spun free

Get the cases hot enough and you'll have a few minute to be able to get things squared away.

If your crank is already centered be careful about tapping the crank too hard because when hot it doesn't take much to slide the crank back and forth.

I found this out later on after changing timing while the bike was still pretty warm. When tapping the flywheel back on it shifted the crank over enough to make the flywheel hit the stator.

Re: Spinning Crank By Hand

I really really don't like hitting across bearings with a hammer, be it brass, plastic, rubber or anything. I'm sure this is one of these things that everyone has an opinion about, but a single shock event like that can cut bearing life in half... you might run for 20 years or it might run for 20 hours but since hitting with something with a hammer is so hard to control, its pretty easy to F it up.

first of all, calm down, nothing is fucked dude! seriously, over the years i've had a few cases come out tight and i've only had one that i had to take apart and scrap the bearings, and it was a minarelli V1 wich are definitely the most annoying to build from that perspective. Tomos/minarelli cases i always use a draw-through tool to pull the crank into the bearing which is already in the case, for that reason.

best thing you can do is what jessie said, heat it up with a heat gun or in the oven to about 350 (that won't hurt the seals) then gently tap on the cases around the bearings, it will usually relax enough to just work. usually just heating them up will let everything wiggle around enough to find its happy place.

then put the flywheel or clutch on by hand just so you have a nice big grip on the crank and turn it over a bunch of times while its still hot, just keep rotating it back and forth until you don't feel any tight spots.

and yeah make sure the whole thing is hosed down with oil. I use 2stroke oil liberally and engine assembly lube in the bearings and wrist pin bearing especially.

Re: Spinning Crank By Hand

Francois Labat /

> Graham Motzing Wrote:

> -------------------------------------------------------

> I really really don't like hitting across bearings with a hammer, be it

> brass, plastic, rubber or anything. I'm sure this is one of these

> things that everyone has an opinion about, but a single shock event like

> that can cut bearing life in half... you might run for 20 years or it

> might run for 20 hours but since hitting with something with a hammer is

> so hard to control, its pretty easy to F it up.

>

> first of all, calm down, nothing is fucked dude! seriously, over the

> years i've had a few cases come out tight and i've only had one that i

> had to take apart and scrap the bearings, and it was a minarelli V1 wich

> are definitely the most annoying to build from that perspective.

> Tomos/minarelli cases i always use a draw-through tool to pull the crank

> into the bearing which is already in the case, for that reason.

>

> best thing you can do is what jessie said, heat it up with a heat gun or

> in the oven to about 350 (that won't hurt the seals) then gently tap on

> the cases around the bearings, it will usually relax enough to just

> work. usually just heating them up will let everything wiggle around

> enough to find its happy place.

>

> then put the flywheel or clutch on by hand just so you have a nice big

> grip on the crank and turn it over a bunch of times while its still hot,

> just keep rotating it back and forth until you don't feel any tight

> spots.

>

> and yeah make sure the whole thing is hosed down with oil. I use

> 2stroke oil liberally and engine assembly lube in the bearings and wrist

> pin bearing especially.

Thanks man.

Unfortunately I didn't see this in time. I did give the crank a couple whacks with a hammer after I heated up the cases. It's freed up now. Big difference.

Looking back, hitting the case would have been smarter. Live and learn. I really hope I didn't affect bearing life too much. Got the cylinder on and it goes nice n smooth. Gets a little suction when going down but I think thats normal.

I really appreciate your response. I'll prob be a little more gentle on the crank/cases next time.

Re: Spinning Crank By Hand

it will be fine!

Re: Spinning Crank By Hand

Francois Labat /

Put cylinder on last night and it goes up and down real smoothly.

Can't wait.

Re: Spinning Crank By Hand

I build using the same method, oven/freezer. After setting my crank and bolting the case I plop the whole mess back in the oven for 20min then bring it out and whack it all around the case sides with a foot long 2x4 then let it sit. always had good results.

Re: Spinning Crank By Hand

^ always a good sign when cheetahchrome agrees with you, it means you are probably right.

Re: Spinning Crank By Hand

Josiah Radebaugh /

A true honor

Re: Spinning Crank By Hand

Francois Labat /

Wealth of information here. I love it. Good to get confirmation.

I like the idea of throwing it all back in the oven. You guys are great. Haven't been had the time to make more progress but hoping to install CDI and variator soon.

Thanks yall

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