DT125MX leakdown test

[DougW]

Building a pretty stock DT125MX engine for junior to ride on the road and greenlane duty, road legal.

Tidied up the transfer entries a bit but rest stock. 

Rebored and new rod , mains and gearbox bearings. 

Leakdown test it went from 5 psi to 4 psi in two minutes, so losing a little from somewhere. 

Soap spray picked up nothing around crank seals, reed cage area or cylinder base.

So could be the exhaust is not sealed properly,  case joint leaking, crank has a sleeve on primary drive gear sealed between crank and sleeve with an o ring ( new oem) , could be there.

Anyway,  I'm thinking 1 psi in two minutes on a cooking trail engine is acceptable?

Opinions please !

[DougW]

Forgot to check if spark plug tight. Now lost about 0.2 psi in 10 minutes.

Think that will do.

Edit. Still at 3.5 psi , from 5, after 5 hours 

Edited December 13, 2020 by DougW

[paul g]

22 hours ago, DougW said:

Forgot to check if spark plug tight. Now lost about 0.2 psi in 10 minutes.

Think that will do.

Edit. Still at 3.5 psi , from 5, after 5 hours 

I always leak down test my motors now and I would be happy with a 5 to 3.5 psi drop after 5 minutes never mind 5 hours!

[2T Institue]

after putting Threebond between the case halves ,on the reed and cylinder base the engine is usually air tight

[DougW]

Motor sounds good with the "Big One" full system fitted and not too noisy.

Bit of a setback in getting it rolling, took old bald back tyre of to fit new tyre, rim is rotten.

New stainless rim and spokes ordered.

Edited January 25, 2021 by DougW