How can I test compression on a bike with no electrics

[struckjm]

I am looking at a parts bike for $200, and excited about getting a sound, high compression engine as part of the deal.

I know how to test when you have a battery and a starter, but what if the bike is disconnected from battery, starter?

Can you hand crank it and get an accurate compression reading (with a wrench at the rotor?).

Are there any tricks to get this info before you buy?

[herennow]

I would guess a roller starter would be your best bet.

Remember that cold compression is a bit of a crap shoot, normally compression is measured warm, so it may not give you much usable info.

[Sporty]

I am looking at a parts bike for $200, and excited about getting a sound, high compression engine as part of the deal.

I know how to test when you have a battery and a starter, but what if the bike is disconnected from battery, starter?

Can you hand crank it and get an accurate compression reading (with a wrench at the rotor?).

Are there any tricks to get this info before you buy?

do a rolling test in in fourth or fifth gear. Roll and then let out clutch (as if you were push starting)

Did you end up buying a leakdown tester and compressor? If you did,  Bring that over and perform a leakdown test

[sledge]

You don't need a relay or the wiring. If the starter motor is serviceable and in place just connect the negative of a 12v battery to a ground on the frame and flash the positive to the terminal post on the motor, the engine should spin.

The other option is to fasten together some pneumatic fittings and a gauge and allow some compressed air into each cylinder and see if it holds pressure. Complicated but not impossible.