First tune attempt - quick questions

[jfm30204]

I am in the middle of my first tune attempt using the following specs and have a couple of quick questions before I continue:

Specifications:
Fill pressure 3000 psi ( use an accurate gauge )
Velocity Screw ( 5/64” wrench ) = turn CW until stops, then 5.5 turns CCW ( don’t forget to remove the set screw first )
Hammer Throw ( 1/8” wrench ) = turn CCW until stops
Hammer Spring ( 1/4” wrench ) = turn CCW until stops, then 3.5 turns CW

Questions:
If I set the VS to 5.5 turns CCW, then there is no more room for a set screw. Is this correct? If so, might the adjustment screw vibrate out and be lost as has already happened to the set screw?

[RogerB]

jfm30204,

Doesn't sound right from my experience with Gen1 Mrod, but I'm sure you've tried it a few times. I would remove the set screw and mark one spot on the edge with nail polish so you can see orientation. Clean top half of threads in hole and set screw threads with very little acetone on a q-tip. Reset the set screw and note orinetation of you mark. Remove the set screw again counting turns to get it out from your 5.5 set point and add a very small drop of locktite and return the set screw to the set location using turns in without going all the way back to the stop. Then at least you'll be able to verify that it hasn't moved. HTH

Roger Barker
Middlefield, OH

[PB_Matrix]

another way to adjust the VVM screw is to:

find a drill bit or other small round tool that fits inside whatever your valve exhaust hole is, lube it with silicon grease, stick it in the hole gently so as not to damage the poppet valve

1 toss the VVM screw & set screw, and fill that hole with metal based epoxy, force it in until it presses against the tool in the valve exhaust hole. Let the epoxy dry. Remove the drill bit, clean up the excess epoxy from the exhaust hole, never worry about the VVM again.

2. use the same drill bit, add a bit of loc tite to the VVM screw, screw the VVM screw in till it touches the drill bit, back it off a 1/8 turn, add loc-tite to the set screw, screw it in till it just touches the VVM screw, then snug it up, hopefully the drill bit comes out easily, if not, remove the set screw, back the VVM screw 1/4 turn from touching the drill bit, then retry the set screw

I like no1 because it gives you a uniform exhaust hole that can be enlarged easily in the future. Leave the VVM screw in and enlarging the exhaust port requires additional steps.

[jfm30204]

I apparently didn't have the valve bottomed all the way before I began the 5.5 turns back. Just being careful, since this is the first time I have tried to fiddle with it.

Thanks for the comments and/or suggestions.