New piston for MZ ES250/2 Trophy

[EmzedRay]

Hello Blurredman. Thanks for your comments. Interesting.

Did MZ stop using starting weights or did people remove them? I understand they were only to retard ignition when starting, to reduce the risk of kick-back, and therefore do nothing meaningful when the engine is running.

I will be digging into mine when the barrel and piston come back and I can start the the reassembly. If they are not there I assume you time the engine as is and it stays where you set it whether it is stationary or running (as there is no advance or retard going on)?
I will post what I discover here, either way.

Here is a photo of the bike. I will post some more of the reassembly and hopefully the sweetly running finished article!

Cheers, Ray

[EmzedRay]

Is is possible to add videos here? I have a nice video of the bike running. I have tried to attach it, but with no success.

[EmzedRay]

Just been thinking (dangerous I know): It a shame there is no manual advance/retard lever like on old British bikes. Now I wonder?.....

[Blurredman]

Hi,

Yes as far as I've ascertained MZ themselves stopped selling the bikes with the starting advance mechanism (which is all it actually is). Indeed on bikes as late as ours we certainly wouldn't have them. I'd guess 1970 or 1971 would be the cut off point when the model that we have was updated in engine power/fuel delivery to be inline with the ETS's 21hp. I don't actually encounter much kick back anyway. And yes the points don't do anything to the engine advance/retard when actually running.

As for timing, it's a bit more difficult owing to the side entrance spark plug, and those appropriate timing tools are difficult and or expensive to buy. I timed my bike up by taking the head off and using a vernier caliper.

You'll easily see if you have advance weights or just a standard cam.

I think the only way to add videos is compress them severely and attach via Zip file, or put them on youtube and link to them.

[EmzedRay]

Here is the link to the video!

https://youtu.be/Sjg0K4JLPZU

Quick question: Has anyone fitted a quick action throttle? Mine goes twice round almost!

Is there a way to do it but keep the original throttle housing?

Cheers, Ray

[EmzedRay]

I stripped the points and dynamo/generator cover last night in search of any advance/retard weights, just in case. Nothing found, although I did not remove the armature winding part as this needs a puller and I cannot see that the weights would be behind there, as there is no room and it (and the points cam) are fixed/bolted to the crankshaft.

So I am assuming no advance weights and will time it at 3mm before TDC by measuring the piston movement before the head goes back on, together with a bulb across the points (new set fitted and gapped to 0.3mm).

It would be nice if I could mark TDC and 3mm before somewhere on the lower engine casing, but there is nothing to reference it to. The flywheel is on the other side to the points and not easy to get to (and runs in oil?).

I will update when the barrel and piston are back from the rebore and she is timed and back in one piece.

Cheers, Ray

[Blurredman]

Cool video:

What tyre do you have on the front- looks like a 3.25 (which I tried to find) or 3.5 and fills out the mudguard much much nicer than a 3 inch.

You can change the throttle, but of course you'd need a new tube and cable and stuff like that... I don't want to do it myself really.


Okay, so you don't have the weights as suspected: I really wish I marked 3mm BTDC and TDC somewhere on the cam and make some sort of reference before putting the head back on, maybe that's something I'll need to do.


Good luck on the installation of new piston.

[EmzedRay]

Puffs, many thanks for your input. Much appreciated.

Yes, I will set the timing with the head off and the new points correctly gapped. As you say with that done it gives a good reference point for the future and all that needs checking is the points gap, adjusting it for wear or when a new set is fitted?

So, shall I go 0.35mm points gap and timed at 2.75mm BTDC?

Thanks again, Ray

[Blurredman]

As my ES250/2 is post 1970, then as specified in the ETS250 manual (with suppliment for ES250/2 made beyond that date with 21hp tuned engines), then the compression ratio of our engines is supposed to be between 9.5 to 10:1.

I use 3mm BTDC as specified in the book. I could deviate on that given the higher octane fuels (as opposed to 79), but it seems okay so I don't mess with it. Besides which, without the timing tool and without making witness marks on the cam lobe to identy as timing positions, i'd have to take the head off and mess with it that way, at least foremost. So I haven't bothered.

That is, if indeed I do have 9.5-10:1 compression ratio. I might not. Something else I haven't bothered to actually measure. Yet.

[EmzedRay]

Collecting the barrel and piston tomorrow, so I can get her all back together and play with these settings a bit. I will post the final outcome and hopefully a video of her running sweetly!

[EmzedRay]

She runs!

https://youtu.be/eAzcIfT8yCI

Thanks for all your help. First kick now.

Also, I forgot who asked about the front tyre size, but here it is:-

https://youtube.com/shorts/4W2waA2MEEk?feature=share

Now I need to run her in and put some miles on.

Cheers, Ray

[Puffs]

That sounds great! Enjoy your trips & let's hope for good weather.

[Blurredman]

Looking good!

And yes, that 3.25" tyre does look better than 3" !! I tried to find 3.25" for my own bike but couldn't find any for a reasonable cost!!



Remember to run it in gently!!