Cam Timing, Dot aligning, Mototrans Elite

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Geordie
Posts: 104
Joined: Thu Jan 16, 2020 12:15 pm
Location: Mallorca, Spain

Cam Timing, Dot aligning, Mototrans Elite

Postby Geordie » Tue Nov 16, 2021 4:37 pm

I was sure I had all timing dots aligned when rebuilding and there were no 2-dot markings. The cam was sourced 2nd hand from what I believed to be a reliable source. The original cam was too worn to be comparable and had a good chance of not being OE anyway. Once assembled, the engine did not start with fuel, compression, spark and spark timing. I decided to source a Dellorto UB24 as correct spec to replace the UB22 it came with - that took some time, piece by piece, but now complete and jetted as OE and also the kickstart spring modification fitted. I should now have an engine as far as practical as original spec varying only by the use of acceptable replacements where OE was not possible. But I had not checked that 2nd hand cam.

The Mototrans workshop manual shows this;

CAMSHAFT TIMING.png


The diagram shows Inlet open 44deg BTDC and the table shows 34deg BTDC. So either 34/73 - 73/38 or 44/73 - 73/38

As fitted, mine reads 41/42 - 65/20 with valve clearances as book and using a 0.05mm feeler. Nothing like the manual even if I'm a tooth out.

cam m-trans.jpg


Anyone know the correct figures for a Mototrans Elite?

Anyone know what cam I might have? And is it a tooth out?

Grateful for any enlightenment :idea:

Geordie
Posts: 104
Joined: Thu Jan 16, 2020 12:15 pm
Location: Mallorca, Spain

Re: Cam Timing, Dot aligning, Mototrans Elite

Postby Geordie » Wed Nov 17, 2021 12:08 pm

A tooth out? Looking at all the listed cams across the range 125cc to 200cc in the workshop manual, they are all symmetrical-ish.

22 teeth on the crank pinion is 16 whole degrees therefore 8 cam degrees. The most logical cam timing from that is a 33/51 - 54/30 when advancing my measured cam by one crank tooth.

If so, what is the cam as its not any of those listed in the Mototrans workshop manual? It is stamped with the identifier "1" [one].

:?:

Duccout
Posts: 888
Joined: Wed Feb 05, 2020 1:20 pm
Location: Essex UK

Re: Cam Timing, Dot aligning, Mototrans Elite

Postby Duccout » Wed Nov 17, 2021 12:58 pm

I have no idea, but Mototrans did use some pretty radical cams in its bikes. Would it be possible for you to find a known cam from someone like Andreas Wolff so that you have the correct starting point?

Colin

Eldert
Posts: 700
Joined: Sun Nov 01, 2009 3:23 pm
Location: Hazerswoude Rijndijk Netherlands

Re: Cam Timing, Dot aligning, Mototrans Elite

Postby Eldert » Wed Nov 17, 2021 4:04 pm

when you calculate the lobecenters you get intake 90.5 and exhaust 112.5 degrees .

i would move 1 tooth over @ bottom and tooth @ top that changes the timing about 8.5 degrees .

the lobecenters then would be 99 and 104 degrees

Eldert

Geordie
Posts: 104
Joined: Thu Jan 16, 2020 12:15 pm
Location: Mallorca, Spain

Re: Cam Timing, Dot aligning, Mototrans Elite

Postby Geordie » Wed Nov 17, 2021 7:31 pm

Thank you Eldert. Very kind of you to do that analysis. I shall be on to it tomorrow.

Ian.

Geordie
Posts: 104
Joined: Thu Jan 16, 2020 12:15 pm
Location: Mallorca, Spain

Re: Cam Timing, Dot aligning, Mototrans Elite

Postby Geordie » Thu Nov 18, 2021 10:02 pm

Yes, one tooth out. The replacement cam is one of those Mototrans with the keyway one tooth different. The bevel gear did not carry the double dot that (I now know) is explained elsewhere on this forum.
Cam intervals not a Mototrans Elite as listed. Will have to see how it runs.


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