Compression test

[nickv1980]

Ive got two z160ho's and just got my hands on a compression tester off a mate and im going to give em both a go and see what numbers i get.

Anyone got any idea what these things should read ? there both good engines with heaps of compression im just after a comparison to go by ....

Any info is greatly appreciated

 

[cloud_2901]

Make sure the spark plug is grounded and the killswitch held while kicking it over with the compression tester in the spark plug hole, to avoid damage to the CDi.

Loose valves would screw with the reading, letting more air past when you crank it over, so a compression tester isn't the best thing to use with a 4-stroke (any motorbike really) to detect leaks / ring condition, a leakdown tester is the one you want. Then you can sit the bike on compression stroke, both valves closed, and pump a certain psi into the chamber and see how much leaks past the rings after half an hr.

But with a compression tester, I'd say anything over 140-150psi would be fine, haven't tested my pitbike but my RM has about 160-170 psi at the moment, half worn top end, and with my finely-tuned leg muscles' senses, there wouldn't be that much difference between the RM and a 150 / 160 pitbike compression wise.

 

[nickv1980]

ok cheers mate i might get a leak down tester

 

[cloud_2901]

ok cheers mate i might get a leak down tester

Unfortunately, they're way more expensive than a compression tester too... I gotta buy one soon as well.

 

[cloud_2901]

MOTION PRO 4 STROKE LEAK DOWN TESTER W/BOX | eBay

This is the one you'd want for bikes, much better price on eBay than local shops.. Still double what my compression tester cost though.

 

[nickv1980]

I can borrow one off my uncle hes a mechanic and does work on bikes cars etc dont think i wanna spend that much really .

But thanks heaps for the heads up mate

 

[sean01]

lol ya read some funny stuff these days..

all tht info and you forgot to tell him to hold the throttle wide open during testing..

compression test is fine to use mate... leak down is the ultimate but for these bikes its over kill...

set your rockers first before comp testing and go from there... you have 2 engines the same so you will see the differences...

 

[nickv1980]

lol ya read some funny stuff these days..

all tht info and you forgot to tell him to hold the throttle wide open during testing..

compression test is fine to use mate... leak down is the ultimate but for these bikes its over kill...

set your rockers first before comp testing and go from there... you have 2 engines the same so you will see the differences...

Ok lol cheers Sean ive got a comp tester here ill give it a go... just done valve clearances on both . Had no idea i had to hold the throttle open

 

[cloud_2901]

Oops, forgot one thing.

Thanks sean.

 

[sean01]

without the throttle wide open the cylinder cant fill which gives low reading on the gauge...

post up your results...

 

[sean01]

without the throttle wide open the cylinder cant fill which gives low reading on the gauge...

post up your results...

 

[nickv1980]

without the throttle wide open the cylinder cant fill which gives low reading on the gauge...

post up your results...

Okay yep makes sense