ENYA Model 5224 Timing

There are eight known variants of the ENYA Model 5224 engines. The .29 IV and .35 III were produced as plain bearing engines with square intake port in the front case. Both were produced as ball bearing “Special” engines with the square intake port in the front case. There were two versions of the ball bearing engines. The early BB engines had a radiused OD on the drive washer, the later BB engines had a stepped OD on the drive washer. Numbers seven and eight were the .29 IV B and .35 III B with a round intake port in the front case. I do not know of any “B” version engines built with ball bearings. The .29 IV and .35 III share a common crankshaft for the various plain bearing types, The ball bearing engines share a crankshaft, so the intake timing should not change with displacement. All timing figures are believed be accurate within one degree.

The plain bearing, square intake .29 IV has 194 degrees of intake timing, 35 degrees ABDC to 49 degrees ATDC. It has 104 degrees of bypass timing, 52 degrees BBDC to 52 degrees ABDC. It has 128 degrees of exhaust timing, 64 degrees BBDC to 64 degrees ABDC.

The plain bearing , square intake .35 III has 201 degrees of intake timing, 28 degrees ABDC to 49 degrees ATDC. It has 114 degrees of bypass timing, 57 degrees BBDC to 57 degrees ABDC. It has 140 degrees of exhaust timing, 70 degrees BBDC to 70 degrees ABDC.

The radiused drive washer BB .29 IV has 207 degrees of intake timing, 33 degrees ABDC to 60 degrees ATDC. It has 106 degrees of bypass timing, 53 degrees BBDC to 53 degrees ABDC. It has 130 degrees of exhaust timing, 65 degrees BBDC to 65 degrees ABDC.

The radiused drive washer BB .35 III has 207 degrees of intake timing, 38 degrees ABDC to 65 degrees ATDC. It has 96 degrees of bypass timing, 48 degrees BBDC to 48 degrees ABDC. It has 120 degrees of exhaust timing, 60 degrees BBDC to 60 degrees ABDC.

The stepped drive washer BB .29 IV has 192 degrees of intake timing, 42 degrees ABDC to 54 degrees ATDC. It has 108 degrees of bypass timing, 54 degrees BBDC to 54 degrees ABDC. It has 130 degrees of exhaust timing, 65 degrees BBDC to 65 degrees ABDC.

The stepped drive washer BB .35 III has 195 degrees of intake timing, 27 degrees ABDC to 42 degrees ATDC. It has 114 degrees of bypass timing, 57 degrees BBDC to 57 degrees ABDC. It has 134 degrees of exhaust timing, 67 degrees BBDC to 67 degrees ABDC.

The plain bearing, round intake .29 IV B has 177 degrees of intake timing, 40 degrees ABDC to 37 degrees ATDC. . It has 108 degrees of bypass timing, 54 degrees BBDC to 54 degrees ABDC. It has 132 degrees of exhaust timing, 66 degrees BBDC to 66 degrees ABDC.

The plain bearing, round intake .35 III B has 199 degrees of intake timing, 27 degrees ABDC to 46 degrees ATDC. It has 110 degrees of bypass timing, 55 degrees BBDC to 55 degrees ABDC. It has 140 degrees of exhaust timing, 70 degrees BBDC to 70 degrees ABDC.

I will have to change the con rod in the radiused drive washer 35 III BB engine and check the sleeve port timing again. The con rod has a lot of slop, and could be affecting the numbers. I don’t have time tonight, I have to pack for the trek to work tomorrow. I will check it out next weekend unless something else eats up all my time.
Someone else who has more knowledge about crankcase compressive two cycle engines will have to say if the differences we see here are any more significant than manufacturing tolerances. The engines represented here cover about a 10 year production span.
Pat King
Monee, IL

Pat, thanks for all the hard work! I'm going out on a limb here and
stating that these variations MUST be due to normal manufacturing tolerances,as I can see no other rational explanation for all the differences. Just to prove my theory,I dug out Peter Chinn's 1964 test of the ENYA 29-IV (plain bearing,square venturi)and compared them to your findings -
Pat's engine - Intake Timing 194 degrees (Chinn's 190)
" " - Bypass " 104 " (Chinn's 112)
" " - Exhaust " 128 " (Chinn's 132)
What is so amazing about all this is,there we were for years thinking that all models of engine within a certain brand were identical,yet there really is vast differences in such basic things as timing. When you add in variations in piston/cyl. fits,differences
in compression ratio etc. etc. - Well! Now we know why some engines are dogs and some are rockets. Is there any old engine makers out there who could express an opinion on this ? BOB [photo not recovered: sipcof.gif]

Pat,

Thanks for a lot of hard work, there. I wonder, did you use a degree wheel for the sleeve timing measurements? I could never get a confident set of readings within less than about 3°...

As for sloppy rod fit affecting timing seriously, consider that for a .35 engine, it takes about 0.005" piston travel per degree around the part of the stroke where the sleeve ports are. GMA pointed this out long ago, and I just rechecked...

Yes, there are considerable 'production tolerances' in our engines. They've improved in recent years, but are still there. Whether they really change a respected good engine into a dog or not, I don't know. ENYA, particularly, does pretty work, and the engines mostly seem to perform well across numerous individual examples of the same "type."

I "time" engines I rework to specific numbers for exhaust and bypass opening - another way to define duration. For Fox 35s, as an example, I set 130° exhaust/120° bypass duration. That can also be described as Ex Opens @ 115° ATDC, Bypass Opens @ 120° ATDC. That's 10° "blowdown" or 5° port lag. Fox 35s have no offset from shaft axis to cylinder axis, so timing is symmetrical: ports close at the same numbers, but BTDC.

To avoid the uncertainty of degree wheel measurements, I worked up a way to use measurements from the pieces in the individual example engine (beats 'tolerances' too). It is actually an analytic geometry approach (sounds scary, but isn't hard to use.) First it was a Basic program, then various other free-standing routines, and now it is in MS Excel.

Seems to work for me...

Lou,
I did use a degree wheel. I use a dial indicator to find TDC. For port timing I shine a flashlight through the exhaust port and call port opening when I can see light at the port to piston juncture. For bypass timing I use the point where the oil film on top of the piston breaks at the bypass port as the opening point. The ENYA engines are symetrical with respect to crank center line and bore center line. As for the .35, I don't think I have another radiused drive washer BB 35 to check. That engine is suspect because the loose rod to crank fit came out of my radiused drive washer .29 after I had bent the crank and rod in the .35 with a starter (fool). That .29 had many runs with 25%, a big venturi, crankcase pressure, and a 7 X 11 Rev-Up prop. The rod is obviously worn out. I do have at least one more radiused drive washer .29 to check out. The .35 in question has at least 200 hours on it and has always been easy to start, and has run strong.
I will open a CAD file on the 5224 geometry to be able to use dimensions to check port timing. I plan to plot some intake port opening and closing area curves to look at port area versus venturi area and versus intake hole area in the crankshaft. There is a lot of the intake event when the port to case area exceeds the hole in the crank. There is a great deal of time when the intake area is greater than the actual venturi area. With a 6.5 mm hole in the venturi insert and a 4 mm spraybar traversing the venturi, the remaining area is not very big. It will be interesting to see what the duration is for the part of the intake event where the flow is strictly limited by the venturi, and the portion that is limited by the crankshaft hole if no venturi is used.

Pat King
Monee, IL

Pat, just as a follow up to this discussion on "manufacturing tolerances",have you ever noticed that when examining engines closely
(even ones of the same brand & size) the top surface of the piston on
some will be either just slightly below,dead level or slightly higher
than the bottom edge of the exhaust port. Would this be due to variations in rod length (centre to centre),the piston itself or the
liner (variations in port height or location in the case)? Maybe a combination of all these! I suppose we could now start a contest to see which was the sloppiest fit engine of all time. I'll start the ball rolling by quoting as an example,the Deezil .12. That great Aussie engine builder Gordon Burford,built a replica Deezil just to show that the basic design was sound - it was just the sloppy engineering in the original that condemned it to be a failure,whilst
Gordon's replica Deezil (using modern materials & top grade workmanship)is a easy starting,smooth running gem. BOB

I've just checked my 3 Enya 35's, two of them are the plain bearing, round intake III B's and the other is a marinised square intake. I set my degree wheel to TDC by using a piston stop tool which contacts the piston at around 10 degrees either side. I'll give the liner figures the way I prefer which is from the point where each port is uncovered on the downstroke. Although it's the downstroke figure I actually take it by moving the piston up to try to eliminate rod bush clearances as best as possible. These are the figures I got but also a little surprise.

PB #1...Inlet opens 33 ABDC, closes 43 ATDC
...Exhaust opens 60 BBDC
..Transfer opens 50 BBDC

PB #2...Inlet opens 31 ABDC, closes 45 ATDC
...Exhaust opens 65 BBDC
..Transfer opens 55 BBDC

BB...Inlet opens 35ABDC, closes 50 ATDC
...Exhaust opens 64 BBDC
..Transfer opens 52 BBDC

Now the surprise. They're a Desaxe design because on all 3 of them there was an assymetry between the opening and closing points of the ports. The closing points were 2 degrees less than the openings. In other words, if the exhaust opened at 60 BBDC then it closed at 58ABDC.

Another point worth mentioning is that the PB crankshafts have a 7mm thread while the BB has a more usual 1/4x28.

I'll check more of the 5224 engines this weekend. I don't have many more PB engines, but have about 12 more BB engines. I never expected these engines to be Desaxe design. I did not check port timing on both sides. As you have noted, all of the PB engines are 7mm X 1mm thread on the crankshaft, all of the BB engines are 1/4-28 crankshaft thread. The .29 III Special racing engine also has 1/4-28 crankshaft thread.

Pat

Bob,
The ENYAs with the seperate front case have about eight tolerances that stack up to determine the location of the top of the piston at TDC and BDC. If all the tolerances are +-.005" the piston top location could vary in relation to the exhaust port by up to +-.040 . Seeing as how the variation is not that great, I would estimate that the tolerances are smaller than +-.005 for most of the parts. It would appear that ENYA is holding many of these parts to +-.001 to +-.002" . That is some pretty fine machining for a mass produced "toy" engine. This weekend should allow me to take some measurements to see what the tolerances look like. The dimensions will also let me make a drawing to see what a graphical method will give for timing of the sleeve.

Pat

Pat,any idea of what were acceptable manufacturing tolerances in full
size aero engines,say a Pratt & Whitney radial,WW2 vintage? BOB.

Bob,
I doubt that things like con rod center to center are tighter than +-.003 on full size aero engines. The differences in deck height in a large engine with timing determined by a camshaft are not as critical as in a small port timed engine. Full size aero engines are not very high performance engines. They are built more for dependability than high performance. If you compare 415HP from a naturally aspirated 301 cubic inch gasoline burning engine versus 2000HP from a supercharged 4360 cubic inch engine, the 4360 can not be described as "high performance". The 4360 can run at rated power for a very long time, the 301 produced it's power in 11 second bursts with rebuilds after every 20 or so runs. High performance engines have all parts hand picked or fitted to minimize dimensional differences and optimize power output. High output model engines are also optimized just like any other racing engine.

Pat

Just goes to show how tolerant model engines can be of variations in the ports and timing. I'll bet all of these engines run decently. The trick is finding the optimum combination for a particular design/purpose and then making sure all the production is optimum.

About the only thing that seems out of whack are the 60 and 65 deg. closing timings combined with the 120-130 deg. exhaust duration timings. 60-65 closings are usually only seen on racing engines. 120-130 on the exhaust is less than a Fox stunt. This may be Enya's way of getting good results with the different venturi sizes. The wilder intake timing may make the engine pick up more rpm with the different size venturis they supplied, even though the exhaust timing is very mild.

Phil,

Good point.

I don't fuss much with shaft timing if it is around 180° total +/-, and 'biased' 30°-40°. Much higher RPM engines do gain from later closing.

I like the way Fox 35s run with 130/120 sleeve duration, so my mods put them there.

ENYA seems to have a liking for late closing of the shaft port. Of all the ENYA 60's,the one most favoured for stunt purposes is the 60-II Model 7032 which first appeared in 1965. In his test of that engine (M.A.N. May 65) Peter Chinn commented on the fact that despite
the cylinder timing being quite mild (exhaust open 62 degrees BBDC,the bypass open 10 degrees later for a total exhaust 124,total bypass 104 degrees) the rotary valve in contrast,remained open for approx. 190 degrees of crank angle,closing at 55 degrees ATDC. Peter
commented that such late closure was usually reserved for racing type engines where peaking speeds may exceed 18,000 rpm. He actually enquired of Saburo Enya the designer,the reason for this,and was told that it had shown to be the only practical means of improving power. The late closing combined with fairly high compression meant that some early models tended to occasionally backfire and kick the prop loose, or even start and run backwards. Doesn't sound like a stunt engine,does it? BOB [photo not recovered: sipcof.gif]