Compression Check ?

[HDKILA]

I bought a compression test gauge with a 14mm and 18mm adapter. The 14mm is too big...It looks like it must be a 12mm...is that correct?

Also what is good compression on an 85 with 31K?

Thanks,
Abe

 

[lankeeyankee]

I bought a compression test gauge with a 14mm and 18mm adapter. The 14mm is too big...It looks like it must be a 12mm...is that correct?

Also what is good compression on an 85 with 31K?

Thanks,
Abe

12MM is correct for the sparkplug threads.
A Leak down test is much more useful to check an engines wear. not only does it check rings it also checks how your valves are sealing.

31K on a VMAX engine, I would hope to see 175-185 dry per cyl not varying anymore than 5.

Dont forget to hold the throttle wide open when cranking..

My current used 85 has 165

 

[HDKILA]

12MM is correct for the sparkplug threads.
A Leak down test is much more useful to check an engines wear. not only does it check rings it also checks how your valves are sealing.

31K on a VMAX engine, I would hope to see 175-185 dry per cyl not varying anymore than 5.

Dont forget to hold the throttle wide open when cranking..

My current used 85 has 165

Do you take all the plugs out at once to prohibit the bike from starting?

 

[lankeeyankee]

Do you take all the plugs out at once to prohibit the bike from starting?

Yes..... Remove all the spark plugs, you dont want the bike to start while performing a compression check and also with all the plugs out the engine will spin faster.

 

[maleko89]

Abe, make sure you stick plugs back into boot and just set on top of valve covers to ground. Otherwise there's a chance of damaging ignition unit.

I made a switch. One lead hooks to where the blue/white wire goes on starter relay. Just unhook the blue/white wire. Other lead just grounded to frame. This just spins the starter motor w/o firing ignition.

 

[lankeeyankee]

Abe, make sure you stick plugs back into boot and just set on top of valve covers to ground. Otherwise there's a chance of damaging ignition unit.

I made a switch. One lead hooks to where the blue/white wire goes on starter relay. Just unhook the blue/white wire. Other lead just grounded to frame. This just spins the starter motor w/o firing ignition.

Great Advice Mark:clapping: I forgot to mention that...:bang head:
Your such a smart cookie!

 

[maleko89]

Am I smart enough to be a fortune cookie?

 

[lankeeyankee]

Am I smart enough to be a fortune cookie?

No only fortune tellers are that smart and since you couldnt tell us the 1/4 mile times for the new 09 VMAX proves to me you cant tell the future.
So your one chocolate chip ahead of the smart cookie

 

[ghostntheshell]

SO:


0.) WARM ENGINE
1.) Remove all plugs
2.) Re-insert them in the boots and lay the boots on valve covers for grounding.
3.) Insert 12mm fitting into plug hole.
4.) Apply full throttle and hit start button.
5.) Read gauge

Does that cover the bases?

 

[spursmech]

unk: Hey, should be done with a warm engine. Later, Spur

 

[Thevmaxrider]

I also disconnected power to the fuel pump AND drained the carb bowls just to prevent the buildup of raw gas in the cylinders. Not too sure if it was necessary, but it made me feel better........ until I hit a cylinder that only had 45psi compression and knew a rebuild was a necessity:bang head:, hence the mod monkey got his teeth firmly into my buttocks.:rofl_200: