Trying to understand cam shaft gearing. Help needed.

[davidgeorge212]

I am somewhat new to engine making and I have never dealt with gears before. I am working off of Martin ohrndorfs v12 engine plans and it shows the gearing in the back end.

They are labeled as cam shaft gearwheel/steel/ Z.-28,-Modul 1

Idler gear for camshaft gear / steel / Z.-15, Modul-1

Is there enough info here to make these or are they purchaseable items?

Any help in helping me understand this will be greatly appreciated.

Thanks
David

 

[Charles Lamont]

Looks like 1-Module gears with 28 & 15 teeth, 6mm thick. Make, or easy to buy. The camshaft gear will, of course, need to be 14T. I dont think I have come across Z as the symbol for the number of teeth but the first thing I find uses it:
https://khkgears.net/new/gear_knowledge/abcs_of_gears-b/basic_gear_terminology_calculation.html

 

[davidgeorge212]

You are right. I know these plans originated in germany and I didnt understand most of the labels, so thankful for Google translate. I just found out Z does represent number of teeth. And apparently modul 1 represents a section or area of the Mädler company which is a German company where I can buy these gears.

Thanks

 

[Jasonb]

Z is often used for tooth number on saw blades throughout the world as well as gears.

MOD gears are in effect the metric equivalent of DP and you should be able to pick them up from bearing and belt suppliers as well as good old e-bay or Amazon. The ones coming out of china are fine for our needs and you should be able to pick them up for about $5 each. Often they are much wider than needed so you can usually get two for the price of one by sawing in half.

 

[Charles Lamont]

And apparently modul 1 represents a section or area of the Mädler company which is a German company where I can buy these gears.

The module is a measure of the size of the tooth. It is the inverse of the number of teeth per millimeter diameter, so your Mod 1, 28 tooth gear will have a pitch circle diameter of 28mm. A Mod 1.5, 28T gear would have a PCD of 42mm.
I should have thought you could get metric module gears in the US, but if not HPC gears in the UK might be a good choice.

 

[Peter Twissell]

Am I missing something here?
A 15T gear driving a 28T gear doesn't give the required 2:1 reduction for the camshaft.
Is the crankshaft gear 14T with 15T idlers driving the 28T cam gears?

 

[dnalot]

The plans may have been from Leonardo da Vinci. He was known to have made his drawings with mistakes that would render the device inoperable to foil those that would steal his ideas.

Mark T

 

[Werkstattkrabbe]

Hallo, ich habe diesen Motor schon gebaut.
Wenn Sie die Zahnräder (Modul 1) so bei Maedler.de kaufen
Alles funktioniert gut.

 

[awake]

Am I missing something here?
A 15T gear driving a 28T gear doesn't give the required 2:1 reduction for the camshaft.
Is the crankshaft gear 14T with 15T idlers driving the 28T cam gears?

David (the OP) did call the 15T gear an idler ... but since he didn't ask about a 14T gear, it does make one think that either the plans are wrong, or he may have missed the fact that there is a third gear size at work.

David, based on the first diagram in your post, assuming that parts # 37 & 38 are 28 tooth gears, then part # 13 MUST be a 14 tooth gear. Otherwise, your cams will not be in time with the crank. Note that in one sense it doesn't actually matter how many teeth are in parts # 43 & 44 - since they are just idlers, they will not contribute to the valve timing. What does matter is that the number of teeth and the position of these idlers are chosen to allow for smooth meshing with the crank gear (#13) and cam gears (#37-38).

 

[Bentwings]

David (the OP) did call the 15T gear an idler ... but since he didn't ask about a 14T gear, it does make one think that either the plans are wrong, or he may have missed the fact that there is a third gear size at work.

David, based on the first diagram in your post, assuming that parts # 37 & 38 are 28 tooth gears, then part # 13 MUST be a 14 tooth gear. Otherwise, your cams will not be in time with the crank. Note that in one sense it doesn't actually matter how many teeth are in parts # 43 & 44 - since they are just idlers, they will not contribute to the valve timing. What does matter is that the number of teeth and the position of these idlers are chosen to allow for smooth meshing with the crank gear (#13) and cam gears (#37-38).

After the correct rotation ratio is determined you will need the cam specs. Usually USA cams are spec Ed at.050”lift then degreed from there. Unknown cams may be from the old days so may be degreed from the very start of lift. It’s very hard to work with this so It might be best the work backwards and determine cam lobe centerline then determine the duration using a “0” point. Many old cams can just be set at equal lift when both valves are open. In any case you need to find top dead center accurately. The hot rod parts suppliers like summit racing and jegs performance can set you up with a nice degree wheel.

 

[Jasonb]

I find the German drawings some of the best model drawings about. Unlike most UK and American model engine plans they actually give detail of tolerances etc as can be seen by the H7 spec for the gear bore for example.

Surely cam lift will be dependant on the size of engine. I've made engines with both larger and smaller lift depending on their size and you certainly won't find any Euro designs with imperial lift values.

Design seem to run OK though

 

[terryd]

That's a lovely engine. A friend of mine, Eric Whittle, here in the UK, now sadly departed, designed and built a very nice award winning Vee 8 engine. He only had a small lathe and bench tools and made it from bar stock, making all the parts except the small BA hex head scrws that he used, but he reduced all the heads of those to a smaller size for a better scale look.. He exhibited it widely in the UK and USA but at one US exhibition it was stolen, but fortunately recovered.

He had some short videos which I compiled for him I'm not sure who made the films it may have been his son. The videos date from 2002 when digital photography was not quite as good as it is today. I thought that you might be interested. Eiric would have been at least 100 years old now



TerryD

 

[jasonh]

btw: z = "zahn" = "tooth"
E.g. zahnarzt = tooth doctor = dentist.
See, it all makes sense!

 

[davidgeorge212]

sorry, I have been away for a little while. Yes the center crank shaft gear is 14 tooth. And yes, of most plans I have found these are very detailed with dimensions and tolerances. I am just working my way through the entire set of plans and instructions to see if there are going to be another things that may trip me up.

He has some pretty good detailed plans on how to make the cam shafts. he has one lobe dimension and then tells what degree of rotation to place each one. It looks like there is a 102 degree rotation between intake and exhaust lobes.