Minarelli v1 piston issues

Rick T /

May 01, 2020 11:25AM

On my minarelli v1 with a 80cc kit, I've blown pistons on this motor in the past, and now I'm ending up with what looks like excess shrapnel from previous breakage. Is there a way to open up these motors to clean out and ensure this doesn't happen in the future? I've got a brand new top end to install but nervous this is gonna happen again.

Second pic is the new piston that did the damage to the head. I had it running for about 5 mins and this was the result. I did a fresh oil change before the damage.

Re: Minarelli v1 piston issues

Brandon Weiss (Detective brandon to you) /

mopedallday

May 01, 2020 12:19PM

Any time you have catastrophic failure of any part of your top end, it almost always calls for splitting the cases. Small bits of metal can hide and come back to bite you, so you pretty much have to get in there to get all of it out.

V1's are not difficult to rebuild, you just have to do your research as with any engine new to you.

Also, changing your transmission oil will do nothing to help in this situation, as the crankcase is completely seperate from the transmission.

Re: Minarelli v1 piston issues

Nick MBC /

khool1499

May 01, 2020 01:02PM

Yeah if there's a bunch of shit in your crank case you run the risk of that shit finding its way back into the cylinder and wrecking the next cylinder/piston you put on it.

Re: Minarelli v1 piston issues

Cameron Cate /

camdogx500

May 01, 2020 01:37PM

If you don't pull the crankcase apart after that you'd better prepare for failed crank/rod bearings in the future.

Might also want to figure out why it ate that ring in the first place.

Re: Minarelli v1 piston issues

baird co /

bairdco

May 01, 2020 06:42PM

That head is toast. Make sure the arrow on the Piston points towards the exhaust.

Re: Minarelli v1 piston issues

Rich Condor /

desmobro

May 02, 2020 07:21AM

I had an issue with the intake I got with a Polini kit ...it wasn’t completely flat on the mating surface ....which caused an air leak.... which made my Moped go faster than ever and seize!

I built a new bottom end and ordered a new kit that was just a cylinder only deal .... same thing happened....

I wondered where the sand or stuff was coming from ....

It was coming in from the intake seal at the head above the reeds....

I used some 1000 grit sand paper and a flat polished piece of marble to sand the intake flat and it hasn’t caused an issue since

Re: Minarelli v1 piston issues

>>>taykoff [s2m] /

taykoff

May 05, 2020 05:25PM

I really can't tell how bad the head is here or if all of the damage was done to and caused by the head gasket. I would advise against running a stock v1 head gasket on a kit, or you run the risk of that gasket expanding into the bore area and getting torn up by the piston...which is what I think has happened here.

You might need a new piston, but you also might be able to sand/file that off and clean it up. Remove the rings to do this work, clean off the piston to remove any debris, and reinstall the rings. You also might be able to save that head by sanding and filing as well...it's worth a shot, and I've seen worse. Then go to treatland.tv and buy a copper head gasket to match your kit, or make your own. Finally, install and blast into the sunset.

Good luck, and keep us posted!

Re: Minarelli v1 piston issues

P D /

pdcomm

May 05, 2020 07:44PM

> >>>taykoff [s2m] Wrote:

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

> I really can't tell how bad the head is here or if all of the damage was

> done to and caused by the head gasket. I would advise against running a

> stock v1 head gasket on a kit, or you run the risk of that gasket

> expanding into the bore area and getting torn up by the piston...which

> is what I think has happened here.

Looks like pieces of ring stuck in the head , to me .

Agreed , I'd smooth things and remove anything not suppose to be there and run it ,provided what we see is the only damage .

Sure there might be a bit of carbon build up in the crevices , but so what ?

Re: Minarelli v1 piston issues

baird co /

bairdco

May 05, 2020 11:23PM

You don't even need a head gasket on a V1. As long as nothings warped and it's clean, it'll seal up just fine and boost your compression a bit.

Re: Minarelli v1 piston issues

Rick T /

trickydick OP

May 06, 2020 08:54PM

Really? I've been pointing the arrow up every time

Re: Minarelli v1 piston issues

Rick T /

trickydick OP

May 06, 2020 08:57PM

Yes I was weary of the old head on this new kit. I have since ordered a brand new aftermarket polished aluminium head, and hopefully salvage this piston. Also I did get a new copper gasket. Moving little by little on this project but will keep updates. Thank you for your advice.

Re: Minarelli v1 piston issues

baird co /

bairdco

May 07, 2020 04:19AM

> Rick T Wrote:

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

> Really? I've been pointing the arrow up every time

"...every time..." So, how many pistons have you had to replace?

If you don't know which way a piston goes, an easy way to figure it out is to make two dots on top of the piston where the ring pins are, then put the piston in the cylinder (without the rings) and see if your dots cross any of the ports, including the transfers. If they do, turn the piston around and try again.

You dont want the ring pins crossing a port, because your ring will go inside and break.

Or you could just look it up...

From polini FAQs:

I’M FITTING MY NEW PISTON. WHAT’S THE DIRECTION OF THE ARROW I FIND ON THE TOP OF THE PISTON?

The arrow must be directed towards the exhaust port.

Re: Minarelli v1 piston issues

Dirty30 Dillon /

hydra

May 07, 2020 03:41PM

Yeah, if you didn't clean out the shrapnel from the first seize, you've been throwing money in the garbage trying to just put a new top end on and go.

Good catch @baird on the orientation. The debris typically follows gravity to the bottom of a horizontal cylinder. So, all the damage should have been on the arrow side.

MOPED ARMY

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