Radial engine cam wheel drive gear issue

[Whittler]

Hi, I am continuing with my Whirlwind J5, 9 cylinder radial build, and have finally reached the point where I am assembling parts! With the kit, which was second hand to me but had not really been started, came some gears, some of which had machining done, for example lightening holes. The cam wheel was complete with internal rim gear and cam lobes machined. The cam wheel as per the drawing and constructors notes would be assembled from 4 parts: The cam wheel itself. Inlet ring with lobes. Exhaust ring with lobes. Internal 80 tooth module 1 rim gear. However, it looks as though my camwheel has been made differently, maybe from just 1 or 2 pieces. It looks as though it was CNC machined judging from the tool path marks on the cam lobes and the internal faces of the cam wheel. The internal rim gear looks either to have been machined in situ ( I don’t know if possible ), or maybe machined or laser cut, and then pressed in. It is impossible to see any evidence of different pieces of metal being used. Note the tooth profile, not having the conventional flats. The 4 securing screws I added, because the drawings said so!

So now the issue. On installing the cam wheel on the crankshaft, and the 20 tooth spur gear in front of it, it is impossible to fit / mesh the 40/20 toothed gears mounted on their shaft. It is close, but no cigar as they say! The 40/20 gears on their shaft are held in an eccentric adjuster, mounted in the engine’s front cover, but the gears will not engage even before I get to that stage. The question is of course: What can I do about it?

it looks to me that the problem is in the gear tooth profile, or their diameter is wrong. The profiles are very different from others used elsewhere in the engine. The individual gears mesh nicely, just not at the 30mm centreline distance that the module 1 calls out for when meshing the 20 and 40 tooth gears.

It would be difficult I think to adjust the rim gear teeth in situ. I could have a go on the spur gear teeth, but it seems wrong to do. I could machine out the existing rim gear and install a new one along with matching stud gears. It’s very frustrating when the issue is one I didn’t foresee, and is not of my own doing - I think!

Anyway I have posted a few pictures, and if anyone has a good work-around, I would love to hear it!



thanks and regards

Paul

 

[mu38&Bg#]

Those don't appear be involute profile gears. Without knowing what profile was used it will be difficult to sort the error. I would guess the profile was fudged without looking at mesh and clearance. Gears don't have to be perfect, but they at least have to mesh without interference. CNC milling gears requires very small cutters relative to the size of the gear tooth. I guess they decided not to bother with small endmills.

If you can put a gear on a document scanner and import it into a CAD program to try to figure out the profile that might be the easiest way to see. I'd be tempted to just make new parts.

 

[mayhugh1]

Paul,
It may not help, but here is a link to a build by a gentlemen in Japan who built the same engine and ran into similar gear mesh problems. His biggest issue was with the supercharger drive gears.

http://modelicengine.la.coocan.jp/j5 index.html
best of luck,
Terry

 

[Whittler]

Thanks for your replies. I swap e mails with Ken in Japan, who is always very helpful. All of his gears show the normal involute profile. The supercharger gears were not part of my kit, so I sourced the gears locally in the UK, and they have involute profiles. I have finished those and they do mesh ok when installed. Interestingly they do not roll around as smoothly as the incorrect cam gears, but at least they have the right centre distance! Can’t have it all I guess! I have ordered a new 80T internal gear and will see if I can machine it to fit the existing cam wheel. Unfortunately not a stock gear with a 3 week lead time. Plenty of other things to do in the meantime!





regards

Paul

 

[Richard Carlstedt]

This will not help you currently , but many years ago a friend built his 9 cylinder radial and I cut the cam ring gears for him at the time. Commercial gears are made on the loose side so there is no " binding" in the customers application.
When i made his gears, I made multiple pinions , each slightly smaller/larger so he could fit them and get the proper backlash. I don't know which ones worked in the engine , but having the correct PD for the application can be critical,
You might look into making your own pinion gears as commercial gear may not fit properly.
Rich

 

[Whittler]

Thanks Rich, that’s interesting to know. I hate to trash what looks like good work on these gears, but I haven’t made gears before, and am not set up yet to do so, otherwise I might have had a go at new pinions. it looks to me like the problem is mainly with the 80t rim gear and mating 20t pinion. I would guess about 1mm out.

 

[Richard Carlstedt]

I have a copy of The Van Keuren Book which gear makers use for quality control measurement. By using a micrometer and two gauge pins , the exact Pitch Diameter can be read, or measured . Van Keuren sells the pins, but they can be made . While I have a set of pins, I have made my own in the past using the shanks of drill bits and sharp lathe tools or abrasives ..
If you can tell me the Pitch and number of teeth, I can tell you the pin size and the micrometer reading. What is wonderful about the Van Keuren method ( which is like measuring lathe cut threads w/ 3 wires ) is it works for odd tooth counts as well. knowing the spur gear size should tell you if the ring gear is good or not.
Rich

The Van Keuren book is actually a catalog and each year they have a new one , but the measuring methods are listed and never change ...a 1970 book is the same tech as a 1995 FYI

 

[Richard Carlstedt]

Here is what it looks like
You can find them at on line book sellers for 3-5 dollars
Rich

 

[Whittler]

Thanks Rich, all are Module 1 teeth. z80 rim gear mates to z20.

z20 on the crankshaft mates to z40

the brass body holding the shaft with the 40/20 spur gears is eccentric, so there should be a bit of wriggle room, but need to get in the zone first.

i think the Van Keuren measurements might assume standard involute tooth profiles? I’m not sure if my non standard teeth should meet the same values. Anyway it would be

 

[Whittler]

I meant to say interesting to try!
Paul

 

[Richard Carlstedt]

You are correct, the Van Keuren Tables only function with standard Involute Profiles , but let me ask a friend who had a Gear business to confirm.
Rich

 

[mu38&Bg#]

With a known profile, measuring would help. What do you do with an unknown profile?

 

[Richard Carlstedt]

My friend is out of town until next week, so I don't have that resource
Will check my library

What do you mean "non-standard teeth "
is it a commercial gear or did someone cut it ?
Rich

 

[Whittler]

Hi Rich,
I don’t know the provenance of these cam gears, if they were made commercially or not. What is apparent when studying the earlier pics, and has been confirmed by others, is that they don‘t have the normal ‘flats’ to the tooth sides and top, but rather are smooth radii. They are different to the other gears I have successfully used for the planetary ’supercharger’ drive at the back end of the engine, and those were commercially made.

I appreciate your interest and help, and like to get to the bottom of things, understand what’s going on and correct if possible. I sent a picture of the gears to a manufacturer here in the UK, and they said they hadn’t seen teeth like them before. So it looks in this case like my options are limited. I can’t make replacement spur gears to the right profile, or buy them it seems! I have ordered the replacement Z80 rim gear, and will try to salvage what I can.

thanks for all your comments and support

regards

Paul