Home › Forums › Free Flight › The Engine Shop › K & B 3.5 and Kin
- This topic has 9 replies, 3 voices, and was last updated 14 years, 3 months ago by Dean McGinnes.
09/27/2008 at 7:10 pm #40954
I have been building some inventory toward moving into Classic Gas, and managed to score a couple of these. One seems to have a different cylinder liner than the other. There is definitely a divider in the exhaust port, making two out of one. On the other, I can clearly see through the exhaust and across the opiston crown and note that there are multiple bypasses. 😕
I have also seen a rc (never capitalize) version and it has no divider.
I thought that some idiot had assembled the engine with the exhause and bypass reversed, but the height of the openings is correct for exhaust timing. 😕
What gives? 😕 😯
If there is someone out there in NFFS-Land that is an acknowledged expert on these beasts, chime in (if it is you) or send me their contact info. 🙂 🙂
Thanques.09/28/2008 at 10:33 pm #46405
I have seen some of each and have no other info.09/29/2008 at 12:30 am #46406
After looking over these engines, I realize how far behind on the learing curve I am. I am sure stuff has been published. If ther is any magazine or newsletter articles out there, on the care and feeding of these engines, I would like to know.
I will also pay copying and postage fees to get my hands on them.09/29/2008 at 2:17 am #46407
Bolt one onto something. Put an APC 7.8×4 on it. Run it on 35% RedMax w/20% oil.
Look for 21,5 k on a tach. If you get that you’ll be in the park. You don’t want to exceed 22k. I think the preferred head clearance is .011. I’ll need to check with a guy. KB plugs seem to work better for mine–good luck on that. A head for a Nelson plug might help.
Keep your tracker antenna isolated from vibration. The wire is prone to fatiguing from a harmonic convergence. Jim Walston can fill you in.09/29/2008 at 4:42 am #46408
Dan, how do you isolate tha antenna? Small fuel line for some length where the antenna exits the transmitter?09/29/2008 at 1:49 pm #46409
I just went to a looser fit for the antenna and used better padding on the xmitter.11/01/2008 at 6:16 pm #46410JLorbieckiParticipant
Divider vs undivided….I wonder if the divided one is an earlier or later version. And here is why…
The piston at the bottom of the stroke is looser in the bore. Thus, it rocks across the wrist pin. Now, put a wide open exhaust, which does cover a fairly wide area. If the piston happens to rock and the top edge of the piston hits the edge of the port, it is a very bad thing. I have seen this, particularly in a ringed engine. So, what the manufacturers do is add a web to keep the piston aligned in the bore.
So, if I was to guess, that was the original intent of the divider. Now, does it hurt performance? My guess is that it would do no harm and if anything would help!
Also, to all, remember that the exhaust port is always the tallest- i.e., closest to the top (flanged side) of the liner…11/05/2008 at 2:31 am #46411
The exhaust on the K & B metrics is on the back of the engine. The web is aligned with the wrist pin, and not perpendicular to it. Therefore, it would have no effect on the rocking you mentioned. 😕11/08/2008 at 4:33 pm #46412JLorbieckiParticipant
You are correct, except that since the bottom of the bore is still sloppy(upwards of .002″ clearance), and there is some clearance in the rod (sometimes upwards of .0015-.002), there still is a chance that the edge of the port will hit the edge of the piston (now this is if the port is very wide…. ).
But I still hate it when someone is correct!12/15/2008 at 2:24 am #46413
I have located an adequate source of gaskets for my 3.5 & 3.25 engines. Still looking for help with gaskets and head shims for my 5.8.
If anyone out there has some, I would be interesting in purchasing a few.
If there is a source for these please let me know. RJL doesn’t admit to having any, only 3.5. 🙁
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