Just picked up a used K&B 40 r/c at an estate sale.  It was stiff from sitting and no glow plug so no way to test compression.  Owner was obviously not available for comment.  Get it home and cycle some fuel through it and got it turning freely again. Stuffed a glow plug in it and viola! No compression.  Ok, I know the piston ring can stick after years of no use.  It was suggested to let it sit with fuel in the cylinder overnight.  Did that, nothing.  Did the same with a penetrating oil, same result.  It was suggested that I heat the motor well with a heat gun, nothing.  Tried starting it today and, amazingly, actually got it to run for about 2 minutes. Sounded ok too.  fuel ran out and flipped the prop expecting compression, still almost nothing. Very little changed from when I got it.
Not sure when it was made, s/n is 0072695.    Im thinking a new piston ring, perhaps new cylinder liner.  Thoughts, suggestions?

Just picked up a used K&B 40 r/c at an estate sale.  It was stiff from sitting and no glow plug so no way to test compression.  Owner was obviously not available for comment.  Get it home and cycle some fuel through it and got it turning freely again. Stuffed a glow plug in it and viola! No compression.  Ok, I know the piston ring can stick after years of no use.  It was suggested to let it sit with fuel in the cylinder overnight.  Did that, nothing.  Did the same with a penetrating oil, same result.  It was suggested that I heat the motor well with a heat gun, nothing.  Tried starting it today and, amazingly, actually got it to run for about 2 minutes. Sounded ok too.  fuel ran out and flipped the prop expecting compression, still almost nothing. Very little changed from when I got it.
Not sure when it was made, s/n is 0072695.    Im thinking a new piston ring, perhaps new cylinder liner.  Thoughts, suggestions?

    This engine uses a Dykes ring, which has very little tension and very little compression when you flip it. It seals up when the engine fires which pushes the top edge of the ring out to create the seal. It's normal not to have much compression.

    Run it fast with a small prop at normal speeds (normal RC speeds, that is, an 8-6 or so with the throttle wide open, and the needle peaked and then backed off just enough to make sure it is not sagging) a few times (maybe a quart or so) . Use a fuel with a lot of synthetic, but a little castor. If it seems to run OK, then you will have to assume it's good until proven otherwise.

   Brett

K&B's generally didn't use head gaskets (or front & rear gaskets) after the "Series '61" engines. Which were not very good, frankly. They eventually got them working fairly well in about '64 or so.

I believe that engine is a model #4050, but I've never had one. I did have a #4055, which was a CL version, and was an ABC. Brett is right about the Dykes ringed engines. If you take it apart, check for cylinder bore gouges from the wristpin. We found that problem around '67 with one we used for rat racing. They really needed a rebuild every year, including piston, cylinder, ring, rod, wristpin & pads. Not real impressive durability, but it was a sweet engine with great restarts (with a good ring). You might be able to get a better ring from our piston ring supplier, down in the vendor's forums.

I went to HS in Pullman with a Dowler...Viki...another USAF brat. Any relation?  Steve

K&B's generally didn't use head gaskets (or front & rear gaskets) after the "Series '61" engines. Which were not very good, frankly. They eventually got them working fairly well in about '64 or so.

I believe that engine is a model #4050, but I've never had one. I did have a #4055, which was a CL version, and was an ABC. Brett is right about the Dykes ringed engines. If you take it apart, check for cylinder bore gouges from the wristpin. We found that problem around '67 with one we used for rat racing. They really needed a rebuild every year, including piston, cylinder, ring, rod, wristpin & pads. Not real impressive durability, but it was a sweet engine with great restarts (with a good ring). You might be able to get a better ring from our piston ring supplier, down in the vendor's forums.

I went to HS in Pullman with a Dowler...Viki...another USAF brat. Any relation?  Steve

Very interesting!  I'll have to look into any Viki's in the family. Most of the family is from Montana.

It's got 4 ports. I did see online that rings, pistons and cylinder liners are available.  I did a check and there is still virtually no compression no matter how fast that prop if flipped. I'm certain that this one is just worn out.

  Maybe, but *you will not get much compression with hand-flipping*, worn out or not. It just doesn't work that way, it requires the pressure of an actual firing (150-ish PSI and up) to do much with the seal. That is a flaw for our purposes, because you can't really tell whether it is worn out or not without actually flying it in a stunt plane.

   If you can get it started reliably, it's probably good enough to get some flights in.

    Brett

Gary  DO NOT buy your ring from MECOA unless  you want no compression  and a very large gap.. I have a dozen here brand new that ALL have huge gaps, The only way to use these in CL  is the way Stan Powell did, he sent his sleeves  to Henry for chroming, and in doing so make the diameter smaller, this made the end gaps  much tighter, and so they were usable, and had compression  to hand crank. My ST dykes Engines   OS  dykes  engines and  my K&B 40  all have decent compression  for hand starting
So get a ring that you can buy with a small or  no gap new, that way you can set the gap tight... starting off at .010 thou  is   NO good

If , as  Motorman says, the new guy doing Frank's rings are  no good, not round and rough, then I am afraid we will have to look for others to make  Dykes  rings for us.

Randy

Thge wrist pin often degrades / corrodes , if anything has . So first check ! .



Pic of IRVINE ring , avaliable via. http://www.hobbystores.co.uk/default.asp?WPG=HOB_HomePage1&PageNumber=1&s=c:0,c:970,c:970-050,c:970-050-040 for a mere 7 pounds 75 p. 

I found my ( one time ) supply fitted excellently to used pistons / took up the slack .
A NEW K&B piston & Irvine Ring , at first seemed stalled , but fit with zero vertical clearance but no binding , after a few cups of tea ,  .

SO the Irvine being a 20.000 plus late ( 80s on ) durable engine , its a ' off the shelf ' item that does the job . Well .

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Think if the abc case & the ring case are the same part No. the liners'd be interchangeable . But grab a new Gudgeon / Wrist Pin , whilst your at it .

Ive seen bronze bushed pistons , for the wrist pin . Assumed it Ex Factory ,  but seemed a bit unusual .

So, can I simply retrofit a ABC sleeve and piston for the current ringed piston and sleeve then?

It can be retrofitted,  but  I do not know all of the parts  needed, I have an ABC   motor  here, I would have to  check out what parts you would need, of if just the  P/S  would work,  I would  FIRST  , look at the Irvine  ring , if it has a closer gap, it would be worth a try


randy

in racing we found that a sharp flip backwards will give u one _ 2 flip starts comp or no comp

     Hi Bob:

     What is backing to start all about?  I find that this is the best method to use when starting my sport engines. 

     I read an article many years ago discussing why there is more compression when the engine is turned backwards but I forget the reason.  Perhaps someone can chime in on this idea.

                                                                                                           Be well,

                                                                                                           Frank McCune

In ringed  engines, they will have better compression in the direction the ring gap sits
If the gap is son the  exhaust side it will have better compression flipping frontways
If ring gap is on the intake side  it will have better compression flipping  backwards

It should make  no difference in lapped motors

Randy

In ringed  engines, they will have better compression in the direction the ring gap sits
If the gap is son the  exhaust side it will have better compression flipping frontways
If ring gap is on the intake side  it will have better compression flipping  backwards

It should make  no difference in lapped motors

Randy

      Additionally, for whatever reason, the gap on some engines wants to migrate to a particular orientation. All my ST46s (maybe 5-6 of them total over the years) had the ring migrate to the  intake side and when not right, had lots of compression backwards but not much forward. Even if you assembled it one way, it moves until it is in the preferred direction.

     One of the things I was going to try to make it more repeatable was get someone to put a pin in the groove, and I was going to file a notch in the ends to keep it in one orientation. In fact I was thinking about how to do it on my way to Golden State in 1988 - but when I got there, there was Paul Walker and the Impact/40VF. After that weekend, no one present thought they should keep trying to make ST46s work!

     Brett

      Additionally, for whatever reason, the gap on some engines wants to migrate to a particular orientation. All my ST46s (maybe 5-6 of them total over the years) had the ring migrate to the  intake side and when not right, had lots of compression backwards but not much forward. Even if you assembled it one way, it moves until it is in the preferred direction.

     One of the things I was going to try to make it more repeatable was get someone to put a pin in the groove, and I was going to file a notch in the ends to keep it in one orientation. In fact I was thinking about how to do it on my way to Golden State in 1988 - but when I got there, there was Paul Walker and the Impact/40VF. After that weekend, no one present thought they should keep trying to make ST46s work!

     Brett

Most all of them did that, so did the ST 40 and  60 , several other engines would do the same, the rings  moved, so I always pinned mine, I used a very small roll pin, it would stay with no problem, you could grind a notch into the inner 2 edges of the ring at the gap, I also sometimes just used a piece of piano wire, and peened  the aluminum over the wire, both ways  was  OK, I drilled down thru the top, my friend Scott would  micro drill the edge of the piston at the ring groove, you could use a piano wire piece and you did not even need  to secure it, as the ring would keep it in place

I have  ABC lapped stuff  for my old  46   51   and  60s

Randy