Hello all:

    Recently, I have been running some old engines that have me confused.  I think that the problems originate with poor cylinder compression. 

    The problems are as follows:

Difficultly in starting

Very sensitive needle valve settings

Very narrow range of speed

Engine quits or sags when battery is disconnected

     The engines in question are four lapped c.i./steel and four aluminum pistons with rings in a steel cylinder. The lapped engines show NO leakage anywhere in the engine.  The p&c fits are great with no leakage and there is no leakage around the plug or head.  The cylinder compression is very low.  The ringed engines have very poor fits of the rings to the cylinder and are not included in this question other than to demonstrate that they too share the same problems.

    Now to the questions: What causes low compression other than engine design?  I am comparing two Veco .19 engines that look the same but one has great compression and the other does not.  I can also do the same comparison with two Fox .29 engines.  None of these engines have any compression leaks.

   What are the cures for low compression other than replacing the p&c with new ones or having the cylinders chromed or pinched?

    I have experienced this problem all of my life with model engines.  Some were great and some would never be any good.

    Any ideas or thoughts?

                                                                   Tia,

                                                                   Frank McCune

     Hi Lauri:

     Thanks for the reply! I will try that today.  Both engine parts "look' identical but a test may reveal something.

                                                          Stay well my friend,

 
                                                          Frank McCune

    The engines in question are four lapped c.i./steel and four aluminum pistons with rings in a steel cylinder. The lapped engines show NO leakage anywhere in the engine.  The p&c fits are great with no leakage and there is no leakage around the plug or head.  The cylinder compression is very low.  The ringed engines have very poor fits of the rings to the cylinder and are not included in this question other than to demonstrate that they too share the same problems.

    Now to the questions: What causes low compression other than engine design?  I am comparing two Veco .19 engines that look the same but one has great compression and the other does not.  I can also do the same comparison with two Fox .29 engines.  None of these engines have any compression leaks.

   What are the cures for low compression other than replacing the p&c with new ones or having the cylinders chromed or pinched?

    I have experienced this problem all of my life with model engines.  Some were great and some would never be any good.

    I am not convinced that the problems you are having are entirely based on the compression (or, technically, the piston/liner seal). I have had all sorts of compression seal levels but not these sort of issues.

     But, overall, the sorts of variations in compression and unexpected variations in the compression and fit you notice are the same as most of us had back in the era. One ST46 would have great compression, the next, felt like you left out the glow plug gasket. As far as I was ever able to determine, the actual batch of iron used for the ring made all the difference. Some batches seemed to have ideal properties, the next might not. I expect the same sort of thing was going on with the pistons, and given that many of them were very poorly made (in terms of quality control) in the first place, it was just a crap-shoot. Thats why we all carried multiple backup engines and a box full of parts, and hoped you could find one that would work on a particular day. The reason people latched on to Fox 35s was not the performance, it was that it was reasonably repeatable from day to day - once you got one that worked, it worked for a long time.

   I hate to say it (again), but the cure to all of this is to use *modern AAC/ABC/AAO/AAplasma cylinder/piston assemblies*. Getting rid of iron piston/steel liner engines, or even worse, ringed engines, was the greatest step forward in stunt since Bob Palmer put flaps on the Go-Devil. That's why I never recommend anyone seek out older engines unless they absolutely have to. Getting a modern engine more-or-less eliminates the sort of wild variations and difficult handling properties you are talking about, and that's why almost no one uses anything else. I haven't thought much about how my piston might be doing since about 1988, it's just off the radar, you gas it up, flip, and fly it.

    Brett

    As stated, there are no leaks and the p&c fits are great!

    Yes, I eid the piston heating, knurling and the striking the piston with a hammer, but all that I got was a warped piston,one that
was knurled and wore out again very quickly or the piston broke at the knurl lines! Lol

    It's not that big a deal, just run them as it was done back in the day - pick the best and use that one, if it goes over the hill, use the next best!

     I have had exactly zero luck with any of the piston-growing tricks, too. The chances of breaking it are pretty darn high compared the likelihood of an improvement.

     Brett

It's a stretch to blame poor compression on the "iron and steel" technology.  Keep in mind that K&B Torpedo, Orwick, O&R, Madewell, and many other 40's and 50's engines were made exactly that way.  They universally had great compression with no leaks, and they stayed good for a very long time, with the correct fuel.

Floyd

I have 8 Orwick engines from the 40's and 50's.   They do very well "cutting mustard".

F.C.

I actually like and used to work on steam locos, I refer them to diesels locos. I run modern engines and I run things like Orwicks on ignition. Both are easy to start both are the same day in and day out.
If you are enticed to get rid of those old style engines, just let me know.

Andrew.

  Hi Tim,   a design engineer might use your formula to determine compression ratios but try raising the exhaust port & see what happens in a 2 smoke engine
  john
 P.S.  I'll be down in 9 days please don't drink all the beer .