70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

A while back, I was doing a long-ish ride in the summer on a 100+ degree day, not pushing hard or climbing hills. Just after sunset on the way home, my 70cc DR kit made a weird plinking noise then died, not to start again.

Running stock carb with 82 jet, and super-stuffy race crankshaft, MLM people's sidebleed pipe. I have a pull start but it was stuck and the motor could not be turned, so I assumed I had seized it.

That day cylinder head temps had been high, but not especially hot, low 400's. The last reading on the Trailtech was 405F.

Finally pulled it apart to find the piston was solidly stuck in the cylinder, not due to melted aluminum as I had expected, but because one of the piston wrist-pin clips had come out and lodged itself between the piston and cylinder wall! Once I rigged a "press" of sorts to push the piston out of the cylinder, I found a little chunk of metal that had chipped off the base of the cylinder :-(

(please see photos)

Also noticed the top of the piston looked pretty well-baked with some signs of blow-by (but I'm no expert), the marks in the photo on the top of piston I made with my "press" while pushing the piston out. The piston rings were so brittle that when I went to remove them, they just cracked apart in pieces. The wrist pin was also so surprisingly stuck in the piston, that I had to rig another "press" with a c-clamp to push it out and separate the piston from it's beloved crank.

How the heck does that happen?! And hope i'm not being Mr. Obvious here, but my cylinder (and rest of the kit) is now toast, right?

_20190818_151658.jpg
_20190818_151428.jpg

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

Jack Rutherford /

piston is toast. can't see inside cylinder but sounds bad

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

Blow by without question. The remaining rings in first pic are still wedged in grooves. Overheated without question. I'm sure the underside of piston dome is charred, but a pic would be nice too. That clip came out and seized it. The bottom of cylinder broke off when you had to force it apart becasue of the wedged circlip. 400 degrees is danger zone and you exceeded that by how much total? Looks to have reached 400 degrees more than once. Everything in pics is toast but I hope rod and crank aren't.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

Jack Rutherford /

somehow I missed the piece of the cylinder that had blown out

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

Captain Janeway /

I had this same kind of blowout on one of mine and that clip trashed the cylinder. Wanted to kick myself. The kit only had about 500 miles on it. I'm guessing the clip just didn't sit right and wiggled loose(edited)

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

Thanks everyone for your replies,.. yep I was afraid the kit is toast. I will try to post pics of the piston underside and inside of cylinder maybe tomorrow after work. For me the bigger question is now if I buy another kit - how do I prevent this in the future? Some things I was already somewhat aware of but didn't bother doing:

1) better head, water-cooled or not, Polini?

2) better carb (Dellorto 21mm PHBG or Mikuni VM20?)

I know stock barely does the job w a 70cc, maybe I was running lean?

3) better intake than stock?

4) I never smoothed-down the sharp edges on the cylinder ports, didn't know that might be a big deal?..

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

:)(edited)

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

> Captain Janeway Wrote:

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

> I had this same kind of blowout on one of mine and that clip trashed the

> cylinder. Wanted to kick myself. The kit only had about 500 miles on it.

> I'm guessing the clip just didn't sit right and wiggled loose

It's a little disconcerting that those clips can pop-out so "easy". I can only hope this only happens after serious overheating.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

> live ɘvil Wrote:

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

> Blow by without question. The remaining rings in first pic are still

> wedged in grooves. Overheated without question. I'm sure the underside

> of piston dome is charred, but a pic would be nice too. That clip came

> out and seized it. The bottom of cylinder broke off when you had to

> force it apart becasue of the wedged circlip. 400 degrees is danger zone

> and you exceeded that by how much total? Looks to have reached 400

> degrees more than once. Everything in pics is toast but I hope rod and

> crank aren't.

I ran over 400 several times and thought it was no biggie, although it did make me nervous and hoped wouldn't go higher. Sorry if this has already been discussed in full elsewhere here, but what would you say is a normal/safe head temp to run on a kitted Hobbit?

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

> Pablo Rivera Wrote:

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

> > live ɘvil Wrote:

>

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

>

> > Blow by without question. The remaining rings in first pic are still

>

> > wedged in grooves. Overheated without question. I'm sure the underside

>

> > of piston dome is charred, but a pic would be nice too. That clip came

>

> > out and seized it. The bottom of cylinder broke off when you had to

>

> > force it apart becasue of the wedged circlip. 400 degrees is danger

> zone

>

> > and you exceeded that by how much total? Looks to have reached 400

>

> > degrees more than once. Everything in pics is toast but I hope rod and

>

> > crank aren't.

>

> I ran over 400 several times and thought it was no biggie, although it

> did make me nervous and hoped wouldn't go higher. Sorry if this has

> already been discussed in full elsewhere here, but what would you say is

> a normal/safe head temp to run on a kitted Hobbit?

I can't say for sure with a 70cc, but this original honda 49cc kit I have on an nc50 express always has run hot wide open on warm days. Its a common complaint with cast iron Hondas. I suppose retarding ignition timing would help. A colder plug only seems to delay the inevitable high temps on mine.

When I took mine apart it looked a little toasty but the rings and landings were not full of crud.

What oil and mix are you using? How many miles on this?

20161005_151856.jpg

(edited)

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

The problem with hobbits is heat soaking. I've got three and each has a unique attempt to mitigate it.

1. 60 cc stocko shocko ...dos cycles motzig obtained jailing head ...major improvement. I used a Cheetachrome pull start because it's got a pa 50-1 crank so one way bearing won't work without major changes.

2. Athena 70 cc kit with derby head remachined and decomp sealed And studs slotted - one way bearing .

3. Mallosi watercooler kit with Bosch 12 v pump, radiator and onotjer one way bearing.

Otherwise u r limited in how u ride your moped. If u keep a Hobbit stock it's designed not to seize because it produces less heat.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

Captain Janeway /

> Pablo Rivera Wrote:

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

> > Captain Janeway Wrote:

>

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

>

> > I had this same kind of blowout on one of mine and that clip trashed

> the

>

> > cylinder. Wanted to kick myself. The kit only had about 500 miles on

> it.

>

> > I'm guessing the clip just didn't sit right and wiggled loose

>

> It's a little disconcerting that those clips can pop-out so "easy". I

> can only hope this only happens after serious overheating.

I think this one I just didn't seat right. User error. I've been riding them for years and it's the only time it's ever happened. I've been told to use clips with no "ears" on them or at minimum only one. I think I got lazy on this one because that was all I had. The two-eared ones are too easy to bend and deform so they don't seat right. Also, the opening on the clip faces towards the bike, not away.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

> live ɘvil Wrote:

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

> > Pablo Rivera Wrote:

>

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

>

> > > live ɘvil Wrote:

>

> >

>

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

>

> >

>

> > > Blow by without question. The remaining rings in first pic are still

>

> >

>

> > > wedged in grooves. Overheated without question. I'm sure the

> underside

>

> >

>

> > > of piston dome is charred, but a pic would be nice too. That clip

> came

>

> >

>

> > > out and seized it. The bottom of cylinder broke off when you had to

>

> >

>

> > > force it apart becasue of the wedged circlip. 400 degrees is danger

>

> > zone

>

> >

>

> > > and you exceeded that by how much total? Looks to have reached 400

>

> >

>

> > > degrees more than once. Everything in pics is toast but I hope rod

> and

>

> >

>

> > > crank aren't.

>

> >

>

> > I ran over 400 several times and thought it was no biggie, although it

>

> > did make me nervous and hoped wouldn't go higher. Sorry if this has

>

> > already been discussed in full elsewhere here, but what would you say

> is

>

> > a normal/safe head temp to run on a kitted Hobbit?

>

> I can't say for sure with a 70cc, but this original honda 49cc kit I

> have on an nc50 express always has run hot wide open on warm days. Its a

> common complaint with cast iron Hondas. I suppose retarding ignition

> timing would help. A colder plug only seems to delay the inevitable high

> temps on mine.

>

> When I took mine apart it looked a little toasty but the rings and

> landings were not full of crud.

>

> What oil and mix are you using? How many miles on this?

> >

I am now strongly considering an aluminum cylinder kit (yes I know more devastating if it *does* seize) and fatter aluminum head (but still air-cooled), maybe even a bigger/better carb and less restrictive intake to take a stab @ cooling this Hot Mama down. Does anyone know anything about exhaust cooling rings?

I was running 60:1 Saber, not sure about the miles, don't have an odometer and my speedo stopped working (would make things fun if I got pulled-over) ;-D

Just came to think of it though, bike was running great at higher altitude ~5000 ft, then I moved to lower altitude ~2500 ft and much warmer temperatures, so DOH! Did I totally goon-it not re-jetting? Was using an 82 jet on stock carb I hadn't cleaned for a while, and feel like I've read about Hobbittss jetting 90-something, 100-something with bigger carbs --- maybe I was running tooo lean??!? ;-o

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

> Marc Friedman Wrote:

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

> The problem with hobbits is heat soaking. I've got three and each has a

> unique attempt to mitigate it.

>

> 1. 60 cc stocko shocko ...dos cycles motzig obtained jailing head

> ...major improvement. I used a Cheetachrome pull start because it's got

> a pa 50-1 crank so one way bearing won't work without major changes.

>

> 2. Athena 70 cc kit with derby head remachined and decomp sealed And

> studs slotted - one way bearing .

>

> 3. Mallosi watercooler kit with Bosch 12 v pump, radiator and onotjer

> one way bearing.

>

> Otherwise u r limited in how u ride your moped. If u keep a Hobbit stock

> it's designed not to seize because it produces less heat.

Marc,

Did you get the PUCHONDA sport touring 46mm head from Treatland to work? I am considering this head with the Wizard 70cc kit and 2mm spacers.... Sure would be nice if it cooled things down.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

> Captain Janeway Wrote:

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

> > Pablo Rivera Wrote:

>

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

>

> > > Captain Janeway Wrote:

>

> >

>

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

>

> >

>

> > > I had this same kind of blowout on one of mine and that clip trashed

>

> > the

>

> >

>

> > > cylinder. Wanted to kick myself. The kit only had about 500 miles on

>

> > it.

>

> >

>

> > > I'm guessing the clip just didn't sit right and wiggled loose

>

> >

>

> > It's a little disconcerting that those clips can pop-out so "easy". I

>

> > can only hope this only happens after serious overheating.

>

> I think this one I just didn't seat right. User error. I've been riding

> them for years and it's the only time it's ever happened. I've been told

> to use clips with no "ears" on them or at minimum only one. I think I

> got lazy on this one because that was all I had. The two-eared ones are

> too easy to bend and deform so they don't seat right. Also, the opening

> on the clip faces towards the bike, not away.

Yep, I thought I had been OCD-careful about making the clips seat right on the wrist pin when I installed but maybe still f-d up?.. Am thinking yes maybe the 1-ear clips (or 0-ear clips) may be the better choice going forward. Had no idea about the direction they face making a difference. Otherwise only way I can understand one popping out would be due to extreme heat / warping

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

> Jack Rutherford Wrote:

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

> Hobbit DR Temperatures

>

> Hobbit DR Temp Control

>

> Hobbit DR running hot

>

> Hobbit DR Kit Overheating

>

> Temperature dilemma Hobbit

Thank you, these are awesome links.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

Pablo the Puch Honda treats sport head I did try and it was a failure. The jailing head at dos cycles works.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

Marc, do you mean the Hobbit 44mm Oversize Head at Dos Cycles (about 50 bucks)? I searched for "hobbit jailing head" but could not find anything..

Sounds like you are running 126mm studs on that, M7 (hole-enlarging) or M6 (no-enlarging =))?

I am thinking about using that head with either the Trick or Treatland 46mm Wizard Kit (and 2mm base plate spacer),.. or if I'm feeling spendy, the 47.6mm Athena kit (looks like also w a base spacer).

The other head I saw on Dos Cycles is the Moped Factory "Big Fin" 47mm (which would go best w the Athena kit?), but that would mean I am feeling particularly-spendy, and need to take someone out for a Steak & Lobster dinner at Seize-ler.

> Marc Friedman Wrote:

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

> Pablo the Puch Honda treats sport head I did try and it was a failure.

> The jailing head at dos cycles works.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

Hey, hey, hey...

Where's that pic of the underside of trashed piston?

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

15667964837984290601722047636776.jpg

This is the dos cycles jailing Hobbit head. I'll post some more in a second. This head works. It's not a squished head btw. But it's massive for cooking and works.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

Screenshot_20190825-222323.png

This is the jailing moped factory ( motzig ) head that is superb. But next I will post something else.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

15667971423678628933857832063815.jpg

Ok now... These are treats Puch Hobbit heads. The one on the left is the 47.6 Athena head. This one has a reasonable mods. The deepest part of the head is nowhere as deep as the right one which is the 46 mm mild one and not to sound to much like Donald Trump but it's an embarrassment that treats when told that over three mm of the standard b6hs stick out and the heat transfer reliably fouls the plug they told me I was obviously in error. . Well it is a pos that I will not sell anyone and why should I be so nice when I asked them to get this out of my life I got lip only. But the other one isn't as severe and faulty machining down so only a mm sticks out and I think it will run perfect if on the Athena. I'm holding onto my modded metrakit head. I drilled both out to m7 and they will slip on just fine. Let me know if u want the left one. Right is not for human use. Sorry Benji but when I contact treats to tell them something isn't right u Betta believe it. I've been at this for a while now. Oh putting a copper washer to make the plug flush. Right ....doesn't work. Too much heat. Spark plugs are designed with the metal around it in mind ... I am in a bit of a foul mood. Must be the heat.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

as you can see, the piston still refuses to be separated from its beloved wrist pin:

20190825_234802.jpg

this is the inside of the cylinder with its unchamfered ports:

20190825_235010.jpg

I dare say if it wasn't for the broken chunk off the bottom, this cylinder would still be usable?

> live ɘvil Wrote:

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

> Hey, hey, hey...

>

> Where's that pic of the underside of trashed piston?(edited)

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

Sweet,.. so this is the Motzig Jailing $50 head that will work?..

But with which kits?

1) Athena 73cc - $185

2) Stocko-Shocko 60cc - $85

3) Trick-or-Treatland Wizard 70cc (is this kit officially garbage w/o an upgraded piston? =)) - $667

> Marc Friedman Wrote:

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

> >

> This is the jailing moped factory ( motzig ) head that is superb. But

> next I will post something else.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

btw, I never checked the ring gap when I installed the DR kit ;-)

Temperature dilemma hobbit PA50II

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

> Pablo Rivera Wrote:

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

> btw, I never checked the ring gap when I installed the DR kit ;-)

>

> Temperature dilemma hobbit PA50II

Piston bottom looks good. Heat was never an issue on this motor. That circlip was though. Chamfer the ports to prevent snagging a ring. Always check ring end gap.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

The stockoshocko is on that red bike with the jailing head buuuuut I had it at a machinist who squared off both top and bottom and decked it. It needs a mlm plate at the base just like the Athena needs one. Go buy anotjer dr, the jailing , and a one way bearing to make it a pedal start without decomp. Or do the Athena and buy that head I posted. I'll sell it to u for $40 plus postage. So $50 but It all ready for m7 studs if u have them.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

Hmm, ok. I may do the Athena, so may hit you up for that squished head. $50 instead of $75 for the head would take some of the Lobster off buying the Athena, even though I have been reading the Athena is a work of art and well worth the extra $.

I went to pull-start, no pedaly for me =)

Will no-decomp still be a problem w a pull-start?

Also, is there anybody out there?....

Um, I mean, that has a Wizard Kit and loves it?

I really want to try and go all-aluminum so all the Hobbits's partses will expand together happily and stay nice & cool under pressure, but I also want to try and save some $ so Wizard Kit looks tempting. Does the Wizard piston really blow(-by) so bad it must be replaced to make the kit usable?

> Marc Friedman Wrote:

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

> The stockoshocko is on that red bike with the jailing head buuuuut I had

> it at a machinist who squared off both top and bottom and decked it. It

> needs a mlm plate at the base just like the Athena needs one. Go buy

> anotjer dr, the jailing , and a one way bearing to make it a pedal start

> without decomp. Or do the Athena and buy that head I posted. I'll sell

> it to u for $40 plus postage. So $50 but It all ready for m7 studs if u

> have them.

Re: 70cc 46mm DR Kit died - Is the Cylinder Toast? - Hobbit pa50ii

yep I was afraid I had a role in my DR's demise.

lesson learned & hard knock taken... =)

> live ɘvil Wrote:

> Chamfer the ports to prevent snagging a ring. Always

> check ring end gap.

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