ES125/1 Points cam worn (or is my crank toast?)

[Jamb0]

Short backstory to start off...

I recently got my hands on a 1974 ES125/1 that had just been imported from Germany. It has 27000km on the clock, and the *story* is that it was restored in 2014 and sat in a garage since, and I'd say the bodywork condition supports this as it's pretty much mint. Only problem is that it ran like an utter pig when I got hold of it, wouldn't hold an idle and sounded like it was running really rich but adjusting the mixture screw did precisely nothing. There were a few obvious problems like the exhaust leaking at the downpipe, an air filter that smelt of damp, no fuel filter, and worn float valve and needle. All of above has been corrected and I also decided to rebuild the entire carb with the factory specified jets for safety because some of them were larger than they were supposed to be. Stuck a new battery in too.

Now the thing won't start at all! To eliminate the bits I've messed with I squirted some easy start in the cylinder and kicked it over but still haven't had any luck, which obviously leads me on the thinking I need to check the electrics. Has a spark, contact breaker looking good (although I have a spare) and timing and points gap is iaw my service manual. However my new concern is the points cam. It looks to be lifting twice, about 60 degrees apart (the first lift appears to be the correctly timed point). The cam was pretty rusty but I've cleaned it up and given the felt an oil. I'm under the impression it's not a worn cam because it would be dropping rather than lifting in the wrong place. Without taking it to pieces (yet), my understanding is that the cam sits on the face of the armature and is held in place by a long screw which goes right into the end of the crankshaft. Has anyone had problems getting the cam seated correctly on the armature? Are there any other ideas that might explain my problems? I obviously wouldn't rule out the cam being worn, but it would be odd seeing as the only wearing item touching it is plastic, so has anyone found their cam to be worn before?

I'm praying that my crank isn't bent, although there are some good signs that it isn't.
- the contact breaker lifting is not inversely replicated on the opposite side of the cam (at least I can't see that it is).
-there are no bad sounding noises when turning over the engine manually or when it was running.

Video of the cam here: https://youtu.be/FXwSGonvD8I

Any help/experience/knowledge/opinions would be hugely appreciated, apologies for the newbie questions but this is something I just cant get my head around! I'm hoping that fixing this will be key to getting the thing going properly and then hopefully I can get a little bit of riding in before winter arrives!

[Blurredman]

Hi,

I don't know much about the ES model, but my points on my etz250 do the same. And if you look at the cam, it is actually occuring at 180 degrees. Which is normal. The cam lobe itself doesn't look that bad to me..

I don't know what else to point out - there are much clever people here than I

[Puffs]

Welcome Jamb0. Sorry, no experience with an ES either.
Nice video; I don't actually know what lift curve my ETZ251 has, I'll have a look next time. I know my Jawa from the same era had a similarly odd lift curve, but there the points stayed open for about half a cycle. Maybe it is a way to manage power drain & coil temperature? I also figured that the hard close at the end, just after BDC, also helped making good contact, to then start charging the coil.

A bent crank pin seems implausible, then you'd have very significant vibrations.

But then the question is why it doesn't run... Normally these things are quite simple & should run, given fuel & a suitable spark. Do you feel proper compression?

[dave47]

Sorry to disagree, but it definitely isn't normal. The points should only break once per rev. They are open about 2/3 of the time. AFAIK a second break is unlikely to be a problem even if it were to produce a "wasted spark" shortly after TDC.
Its easy enough to remove the bolt, remove the cam, and inspect it for wear or faulty manufacture, and replace it securely seated. Also see if there is any play in the crank eg bad main bearing.

[Puffs]

Well I don't know what's normal for the ES125/1, but maybe you can see it on pics of that cam, from various traders. Such a cam is actually not that expensive.

If I get to it, will have a look at my 251 & let you know on that lift curve.
What I said on the Jawa was true, and that odd lift curve was one of the reasons I replaced those electrics (--> Vape).

[dave47]

I don't need to look at pics, I've got one here, and checked it with a vernier before making my previous post. Theres nothing complicated about its lift curve. It goes up, it goes down.

I wasn't disputing what you say about the Jawa. I was "disagreeeing" more with Blurredman's post, about it being normal for MZ.

[dave47]

@ jambo
Set the timing to 2.5mm btdc rather than 3.0mm, if you haven't already done so. It is said to make starting easier.

[Jamb0]

Thanks for all of the responses.

I found a compression tester hiding in the garage and got a reading of ~130psi which in my mind is pretty good.

I agree @Dave47 , it would be counter productive to lift the contact a second time (thus potentially producing a second spark) as this would purely reduce the size of the intended spark. However, where you say the contact should be open around 2/3 of the rotation, this would potentially suggest that the contact is actually dropping down where it is supposed to stay open between the two lifts because they're both less than 2/3s apart. This could well have been caused by wear of the cam (even though I could not explain why it had worn down).

Thanks for pointing out the timing, at the moment it is set to 3mm btdc as per the manual, but I shall set it back a little and see if it helps at all!

Next step is to take off the cam and see what I can find in terms of wear or bad seating.

[Jamb0]

A little update/closure.

I think I've got it figured out, the armature bolt was bent!

Another video: https://youtu.be/OoZYL9NN_Ds

I could see how distorted it was while I was unscrewing it, and am now confident that the crank is straight because there appears to be no distortion on the armature in comparison to the bolt, suggesting that all of the problem lies in the bolt. How it got so bent is a question I doubt anyone could answer, but at least it's a cheap/easy fix... The cam does however have some weird scoring on the high part, don't have a clue how that could have happened but almost looks like someone took a pair of vice grips to it in an attempt to get it off (it was pressed on really tight, but I managed to get it using a plastic trim tool). I think I'll replace the cam too just to be safe.

In other news, I (stupidly) didn't even bother to test the the HT lead until today, and after connecting my multimeter found a reading of 10K ohms, which seems way too high even if the cap did have a resistor fitted, so that'll be getting replaced, too. Chances are the issues starting the bike were caused by this in the first place! I've yet to test out the coil but seeing as its an original mz one with a manufacture date of Jan 1980, I may just replace it as a matter of course.

Oh and I lied about my compression, actually closer to 115 PSI, although that still seems pretty reasonable

[Puffs]

OK, then someone knocked it, it seems.

On my 251 I measured 8.75bar, but it has a thick base gasket which reduces the CR. Your 8bar is slightly lower, but yours is a 125 and I don't actually have a clue what any of these 2T MZ's should have. It also depends on how enthusiastically you kick during the measurement (with full throttle). My question was just about how it felt, subjectively.

I run my 251 without R in the cap and without R plug. Not sure if the DDR bothered with R's in either, back in '80. And I still have the original coil, while mine is 9 years younger than yours I don't see any point in replacing a part that works well.

[dave47]

Glad you're making progress.
Its hard to understand why somebody would refit obviously damaged parts, but hopefully there are no more bodges.