Honda Hobbit STILL no compression

Jessie Paull /

I'm freaking stumped. Months ago I over torqued my cylinder and snapped a bolt off in the case, which kicked off a series of events that resulted in my bike having no compression and having done the following:

- New stock piston with pre-installed rings

- Rehoned stock cylinder

- New head and base gaskets

- Cylinder studs to replace the bolts

Could it be the cylinder head or something?

Re: Honda Hobbit STILL no compression

Jessie Paull /

I've also sprayed soapy water around the case and cylinder and don't see any bubbles when I'm pedaling. Thing just doesn't want to start..

Re: Honda Hobbit STILL no compression

Have you checked the decomp? The valve is literally there to give no compression so that could be a problem if it's stuck open or something. So when you pedal it it's got no resistance, the flywheel spins and the motor puts along but it's just got nothin?

Re: Honda Hobbit STILL no compression

Jessie Paull /

> Nick Haber Wrote:

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

> Have you checked the decomp? The valve is literally there to give no

> compression so that could be a problem if it's stuck open or something.

> So when you pedal it it's got no resistance, the flywheel spins and the

> motor puts along but it's just got nothin?

Basically yes, but it does have a *little* resistance, just not very much. When I pulled the do compression it has even less resistance (as expected) so it seems like it's closing. Maybe it's not making a good enough seal?

I pulled the head off again and it's a little dirty I guess, but I can't tell if there's anything really wrong with it

IMG_20200906_165550.jpg

Re: Honda Hobbit STILL no compression

Jessie Paull /

I'm only getting about 25 PSI with a tester

Re: Honda Hobbit STILL no compression

Being as you have the head off , pull the valve and lap it in .

Then there's that question answered .

Re: Honda Hobbit STILL no compression

Yeah lapping the valve is the best way. Buy some lapping compound, Google how to lap valves and bam you've got it

Re: Honda Hobbit STILL no compression

Jessie Paull /

I'll go out and get some lapping compound tomorrow and try that, thanks.

In the meantime I took some WD40 and a wire brush to it and cleaned up most of the carbon

IMG_20200906_174718.jpg

Re: Honda Hobbit STILL no compression

Much better^ . ;)

judging by the amount of carbon on the head , there's a good chance the rings are carboned in place and unable to move . That might account for or at least add to the possibility of low compression . (edited)

Re: Honda Hobbit STILL no compression

Jessie Paull /

Still no luck after cleaning up the cylinder head and lapping the decomp valve - compression still around 25 PSI and won't start

The piston and rings are brand new. Any other ideas? Could the rings not be seating, could I have not honed the cylinder bore enough?

Re: Honda Hobbit STILL no compression

What is the ring end gap ?

Re: Honda Hobbit STILL no compression

u might try lapping your head and cylinder top to ensure its flat, and you are using a new head gasket yeah? looks like freash gas is all around head.

Re: Honda Hobbit STILL no compression

Okay, so what's your cylinder look like? Are your rings gapped and installed correctly?

Re: Honda Hobbit STILL no compression

Jessie Paull /

Appreciate the responses - just pulled the head and cylinder back off to check things out some more

IMG_20200908_144424.jpg

What looks like fresh gas is just two stroke from when I lubed all the gaskets during initial installation. The head gasket *was* new; do I need to replace it again when I put everything back together again?

This piston had the rings pre-installed from Treats, but I took them out to measure the gaps and got .02mm for the top ring and .016 mm for the bottom ring.

Re: Honda Hobbit STILL no compression

The ring gaps seem close enough .

What is the piston to cylinder clearance ?

That should be measured a couple different places through the cylinder .

Re: Honda Hobbit STILL no compression

Jessie Paull /

> P D Wrote:

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

> The ring gaps seem close enough .

>

> What is the piston to cylinder clearance ?

>

> That should be measured a couple different places through the cylinder .

Sorry I'm not exactly sure how to measure that - is that the difference between the diameters of the cylinder bore and piston?

Re: Honda Hobbit STILL no compression

> Jessie Paull Wrote:

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

> > P D Wrote:

>

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

> > What is the piston to cylinder clearance ?

> that's the difference between the diameters of the cylinder bore and piston?

Yes . Unless you have an inside caliper , like below , measure top and bottom of the bore and the piston in a couple places from the landings to the skirt bottom .

Re: Honda Hobbit STILL no compression

I realize now you said you rehoned the stock cylinder. I'd bet money you took too much off and wound up overboring the cylinder, that's basically the only thing left that could cause the no compression

Re: Honda Hobbit STILL no compression

Jessie Paull /

> P D Wrote:

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

> > Jessie Paull Wrote:

>

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

>

> > > P D Wrote:

>

> >

>

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

>

> > > What is the piston to cylinder clearance ?

>

> > that's the difference between the diameters of the cylinder bore and

> piston?

>

> Yes . Unless you have an inside caliper , like below , measure top and

> bottom of the bore and the piston in a couple places from the landings

> to the skirt bottom .

Gotcha - I'll have to pickup some calipers and check it out. Thanks

> Nick Haber Wrote:

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

> I realize now you said you rehoned the stock cylinder. I'd bet money you

> took too much off and wound up overboring the cylinder, that's basically

> the only thing left that could cause the no compression

As much as this would suck I almost hope this is the case just so I can know what the damn issue is. I've been tempted to throw in the towel and pull the trigger on a DR kit, but I'm also worried that I'll get a kit and have the thing still not start on me -_- just really wanted to get it working stock again first

Re: Honda Hobbit STILL no compression

> Jessie Paull Wrote:

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

> just really wanted to get it working stock again first

That is a good way to go .

Re: Honda Hobbit STILL no compression

U can see where its leaking along the decomp passage, take that cylinder to a FLAT surface with some sandpaper ROUGH 150 to start, finish with 600, you'll see that is low along the decomp edge with the black gum.

Do the same with the head. Please do not hit the darn aluminum head with a wire wheel, all u doing is loosing compression with all those scratches. Sand those all out on a Flat surface, cleaning the surface periodically with some compressed air, I use a small granite chunk.

Re: Honda Hobbit STILL no compression

Jessie Paull /

> pat splat Wrote:

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

> U can see where its leaking along the decomp passage

> ...

> you'll see that is low along the decomp edge with the black gum.

So just trying to make sure I understand correctly - you're saying this is indicative of a leak along the decompression passage:

Capture.PNG

And that likely the cause is that the surface is lower in this area, so the goal is to sand the cylinder and head down so both surfaces are completely flat and level?

Re: Honda Hobbit STILL no compression

> Nick Haber Wrote:

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

> I realize now you said you rehoned the stock cylinder. I'd bet money you

> took too much off and wound up overboring the cylinder, that's basically

> the only thing left that could cause the no compression

I'm with Nick on this one, makes the most sense. Can somebody send this man a stock cylinder?

Re: Honda Hobbit STILL no compression

Emil Kniemel /

> Mike Boyd Wrote:

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

> > Nick Haber Wrote:

>

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

>

> > I realize now you said you rehoned the stock cylinder. I'd bet money

> you

>

> > took too much off and wound up overboring the cylinder, that's

> basically

>

> > the only thing left that could cause the no compression

>

> I'm with Nick on this one, makes the most sense. Can somebody send this

> man a stock cylinder?

This was my guess as well. But I say go for the DR and don't look back.

Re: Honda Hobbit STILL no compression

Pull the studs and put the bolts back in. Some studs don’t have enough thread to torque. Some studs also bottom out in case and don’t torque down correctly

Easy try before you sand.

Re: Honda Hobbit STILL no compression

> Jessie Paull Wrote:

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

> > pat splat Wrote:

>

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

>

> > U can see where its leaking along the decomp passage

>

> > ...

>

> > you'll see that is low along the decomp edge with the black gum.

>

> So just trying to make sure I understand correctly - you're saying this

> is indicative of a leak along the decompression passage:

>

> And that likely the cause is that the surface is lower in this area, so

> the goal is to sand the cylinder and head down so both surfaces are

> completely flat and level?

along that whole edge, youll see after a couple of passes, cylinder being steel is much more forgiving than the aluminum head, get all the scratches out. reusing old gasket is fine.

Re: Honda Hobbit STILL no compression

Updates?

Re: Honda Hobbit STILL no compression

Did you check the valve timing? Also the valve/tappet clearance.never worked on the hobbit but rebuilt a few pushrod C100 Cub engines . Put your finger or thumb over the spark plug hole and see if you have any compression. This should be an easy problem to diagnose . I bought a non running engine off EBay . The kickstart shaft was broke but I just finished replacing the broken one on my 1965 Cub . The timing gears were off 180 degrees .the piston was upside down as were the rings. It also had the wrong piston as it stood 1/8 inch over the cylinder.Then on another engine they had the valves cranked down so much they weren’t closing on the compression stroke.

Re: Honda Hobbit STILL no compression

No valves on a Hobbit.....

Re: Honda Hobbit STILL no compression

> Tim Doll Wrote:

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

> Did you check the valve timing? Also the valve/tappet clearance.never

> worked on the hobbit but rebuilt a few pushrod C100 Cub engines . Put

> your finger or thumb over the spark plug hole and see if you have any

> compression. This should be an easy problem to diagnose . I bought a non

> running engine off EBay . The kickstart shaft was broke but I just

> finished replacing the broken one on my 1965 Cub . The timing gears were

> off 180 degrees .the piston was upside down as were the rings. It also

> had the wrong piston as it stood 1/8 inch over the cylinder.Then on

> another engine they had the valves cranked down so much they weren’t

> closing on the compression stroke.

Hobbits a 2 stroke lol, totally different powertrain than the pushrod Honda's

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account