Peg pilots

[superbike]

I have been having trouble with concentric seats with my peg fm1

I have tapered pilots with a locking nut at the bottom.
I would like to try other types like the serdi live pilots but i cannot seem to find any pilots at all with the top size 0f .372 . All the other pilots newen serdi are sized at .375 inch

I have contacted fondera and they have limited pilots and the expandable wich i would really like to try has been discontinued.

chris

[Guy Croft]

Chris, if those Peg pilots are tapered at the top with a little collet at the bottom that is secured with the nut, and you cannot get concentricity - the problem is definitely the guide bore not the pilot, that is assuming you have the right size for the guide.

GC

[superbike]

These guides are well known for this problem. If you fit a new guide into one of thease you usally see a lot of daylight through it afterwards and it needs a heavy cut to correct.

Iam having my own guides made at present but i cannot use on every application. Do i have any other choices on pilots ? Whats your expandable pilot like ?

[Guy Croft]

Chris, hi

The guide bore is the datum centre for whatever pilot you use. The reason Peg is so much better than anything else is that the pilot centres on ends of the guide. This is the way to get accuracy.

Sorry - I know this: You cannot expect concentricity with a dud guide bore with any other pilot and will never get it whatever you use. And if you try you get the risk of wearing away the seat trying to true the thing up. Don't go there. Get good guides.

GC

[superbike]

I got you

even if the brand new guide has not got a hole smack down the middle the top taper of the pilot will pick it up all wrong. Is this correct ?

If i used a straight pilot (no taper) wich was a snug fit into the guide it would have a better chance yes ?

[Guy Croft]

Chris, hi

The pilot top and bottom tapers, provided the hole is round at entry and exit of the guide (ignore the bit in between because the pilot doesn't touch it) - will always position it precisely co-axial with the guide bore - that is to say - coaxial with the top and bottom holes, which amounts to the same thing. Those holes are the datums really.

Consider the guide bore as a cylinder formed around an axis drawn between the centres of those two holes.

If the entry and exit holes are worn - or not circular within reasonable limits - you will never get good concentricity of valve to seat, any more than you will using a solid pilot, parallel or tapered, however snugly fitting. And if you have a guide with bores that are out-of-round at top or bottom either due to bad mfr or wear - they have to come out or you will end up machining away the whole seat insert to true the thing up.

The acid test is that if the valve doesn't lap a nice grey contact face onto the insert within seconds - the seat is just not true to the guide. If the seat greys-up but the vale doesn't, the valve's bent.

GC