OS-91 Head shim and other ?s
06-02-2006, 09:06 AM
#1
OS-91 Head shim and other ?s
Hello all, I recently changed the head on an OS-91 from the small head to the Byron head. This has raised a cfew questions.
1) I damaged the head shim slightly during installation and need to acquire new ones, does anyone know where I can get them?
2) Is the order that the head bolts are tightened and the torque critical?
3) How many foot pounds of torque should the head bolts be tightened to?
4) How do you know if the compression is too high and additional shims need to be added?
5) Is the only difference between the Byron and non Byron versions of the OS-91 the head?
It is a brand new engine so I want to be careful not to destroy it.
Thank you very much for any assistance you can provide.
Anthony
1) I damaged the head shim slightly during installation and need to acquire new ones, does anyone know where I can get them?
2) Is the order that the head bolts are tightened and the torque critical?
3) How many foot pounds of torque should the head bolts be tightened to?
4) How do you know if the compression is too high and additional shims need to be added?
5) Is the only difference between the Byron and non Byron versions of the OS-91 the head?
It is a brand new engine so I want to be careful not to destroy it.
Thank you very much for any assistance you can provide.
Anthony
06-02-2006, 11:05 AM
#2
My Feedback: (48)
RE: OS-91 Head shim and other ?s
Anthony,
1) You should be able to order one through your local hobby shop, or from Tower Hobby.
http://www2.towerhobbies.com/cgi-bin...?&I=LXCM86&P=7
If you have any jet guys in your club one of them might have a spare laying around. I might
have a used one I could mail you if you strike out.
2) The head should be tightened down in several stages. Tighten every other bolt a little bit.
After the first three do the next three. Repeat the process with a little more torque, then
again until fully tight.
3) I don't know the spec. They should be tight but be careful not to over tighten. After break in
re-torque them, then re-check them every 5 flights or so. Do not use Locktite on the head
bolts, all other bolts on the engine should be Locktited.
4) One shim should be enough if you are using 5 or 10% nitro fuel. If you hear any knocking or
pre-ignition then you may need another.
5) Yes.
Joe
1) You should be able to order one through your local hobby shop, or from Tower Hobby.
http://www2.towerhobbies.com/cgi-bin...?&I=LXCM86&P=7
If you have any jet guys in your club one of them might have a spare laying around. I might
have a used one I could mail you if you strike out.
2) The head should be tightened down in several stages. Tighten every other bolt a little bit.
After the first three do the next three. Repeat the process with a little more torque, then
again until fully tight.
3) I don't know the spec. They should be tight but be careful not to over tighten. After break in
re-torque them, then re-check them every 5 flights or so. Do not use Locktite on the head
bolts, all other bolts on the engine should be Locktited.
4) One shim should be enough if you are using 5 or 10% nitro fuel. If you hear any knocking or
pre-ignition then you may need another.
5) Yes.
Joe
06-05-2006, 07:07 PM
#5
My Feedback: (48)
RE: OS-91 Head shim and other ?s
Yes, the problem with Locktite on the head bolts is that you may not be able to tighten or remove them later due to exposure to high heat. Also due to the unequal expansion/contraction of aluminum and steel the head bolts need to be retightened periodically.
There are probably a few guys out there that did it and got away with it, but in general Locktite is not recommended on the head bolts.
Joe
There are probably a few guys out there that did it and got away with it, but in general Locktite is not recommended on the head bolts.
Joe
06-05-2006, 07:17 PM
#6
RE: OS-91 Head shim and other ?s
ORIGINAL: joeflyer
4) One shim should be enough if you are using 5 or 10% nitro fuel. If you hear any knocking or
pre-ignition then you may need another.
4) One shim should be enough if you are using 5 or 10% nitro fuel. If you hear any knocking or
pre-ignition then you may need another.
kc
06-05-2006, 08:46 PM
#7
RE: OS-91 Head shim and other ?s
NEVER LocTite the head bolts---You don't want to over-torque as you will strip the threads. I always used two head shims and mixed my own fuel to a 7.5% nitro content. (Take a gallon of 10% and a gallon of 5% to achieve this) I found that with two head shims the engine puts out a better smoke trail, easily enabling you to see if you are too lean. Also, the engine is much more needle friendly--In other words the mixture control has more range instead of being too lean or too rich a few clicks off of the mixture's sweet spot. Very experience modelers using this engine recommend that anything over 5% requires another head shim. Another benefit of an extra head shim is increased glow plug life---I got 20 flights on a plug and changed it only due to being concerned about it failing...The McCoy MC-9 ducted fan plug is THE plug to use...
I've run these engines in just about every popular fan unit....VioJet, Byron, RamTec, Dynamax--With a little care and a proper mixture control these engines will last a long time..The engines used in Byron fan units WILL run hotter---You ABSOLUTELY need to use a mixture control to get the longest life out of the engine as as the engine gets hotter, is becomes more lean. There are a few mixture control units on the market---I've had very good use out of the BVM mixture control as it has a great mixture range..
I hope this helps...
Kevin
I've run these engines in just about every popular fan unit....VioJet, Byron, RamTec, Dynamax--With a little care and a proper mixture control these engines will last a long time..The engines used in Byron fan units WILL run hotter---You ABSOLUTELY need to use a mixture control to get the longest life out of the engine as as the engine gets hotter, is becomes more lean. There are a few mixture control units on the market---I've had very good use out of the BVM mixture control as it has a great mixture range..
I hope this helps...
Kevin
06-06-2006, 08:44 AM
#8
RE: OS-91 Head shim and other ?s
Kevin and everyone else...
Thank you very much for the advice. When I get home this evening I will remove the head bolts and clean as much of the Loctite as possible off of the threads. The engine has never been run so it should not be that much of a big deal.
I have the BVM in flight mixture installed and plan on using the comercially available 5% nitro ducted fan fuel (i don't remember the brand but it came highly recommended Wildcat I think). My plan is to fly it in my Byron set up with a relatively lean take off mixture and richen it as the flight goes on. Since my plane came out relatively light at under 13 pounds (TGA F-15) I don't expect to have to ring every drop out of the engine to get it to fly.
Thanks again for all of the helpful info.
Anthony
Thank you very much for the advice. When I get home this evening I will remove the head bolts and clean as much of the Loctite as possible off of the threads. The engine has never been run so it should not be that much of a big deal.
I have the BVM in flight mixture installed and plan on using the comercially available 5% nitro ducted fan fuel (i don't remember the brand but it came highly recommended Wildcat I think). My plan is to fly it in my Byron set up with a relatively lean take off mixture and richen it as the flight goes on. Since my plane came out relatively light at under 13 pounds (TGA F-15) I don't expect to have to ring every drop out of the engine to get it to fly.
Thanks again for all of the helpful info.
Anthony
