MZ skorpion ,connecting rod

[bikeseamus]

Correction
                   SAE stands for Society of Automotive Engineers.

  You have that over there?

   PS.  Thanks for checking up on the running lights, but don't worry about them too much.

  Should you someday run across a breaker with enough sense to sell them reasonably, we can go from there.

    In the meantime, I will innovate with any number of lighting options.

               Thanks again,   Jim

[guest146]

Just out of intrest what the thing with these MZ con rods.

What fails  Big end. Small end. Most single cylinder big ends will knock for quiet a while what the thing with the MZ ones

Ken

[Ian]

Just out of intrest what the thing with these MZ con rods.

What fails  Big end. Small end. Most single cylinder big ends will knock for quiet a while what the thing with the MZ ones

Ken

Hi Ken,
The small end and the piston pin wear allowing the piston to be dragged down the bore leaving scoring in four places.
Or is it the piston rings wearing out that allows the piston to be dragged ?
Some of this might be down to previous owner neglect .
Basically the standard con rod is the weak point of the engine .
It's also the same con rod in SZR and XTZ so don't buy a neglected one.
If you fit a high compression piston a standard con rod lasts 15 minuets of gentle riding this was a perfect con rod !
I've since been told it can snap as well !
On top of that it costs a lot  of £££££££££££££$$$$$$$$$$$

[Ian]

Hi bikeseamus,

Are you tyring to do my head in with all this talk about oil ?
Just been to the Silkolene web site they recommend.

Skorpion and SZR  15/50 or 20/50   XTZ 10/40

Obviously I need to change to 15/50.

Regarding the con rod ,I've sent loads of Emails ,today I've received 3 replies ,all from the UK .

1st one, rod kit £92.00 ,fitting £112.00
2nd one, rod kit £189.71 + VAT fitting around the £650 mark + VAT
3rd one, new race rod on the crank fitted £200.00

1st and 3rd need to answer a few more questions before I trust them with my cranks.
Not to sure what the 3rd one is quoting £650 + for ?

Jim,
If there con rods aren't of a known make I'll take you up on your kind offer of shipping them to me.
Many thanks...........Ian

[andy230]

My tuppence worth:

I have a 1998ish Skorpion, engine thus:

Owner1 wrecked it- bottom end got noisy, he kept running it, eventually sheared the crankpin
Owner2 bought it, sent it to Slipstream, hi comp piston in 660 bore, flowed & ported head, dynojet kit in standard carbs.  New bearings throughout, new standard rod, crank trued, new crankpin.  52bhp at wheel, used as a trackbike for a couple of years, but well maintained.
Owner3 is me, 6000 miles later its lovely, bounces off the limiter with ease, no probs re lower end with hi comp piston and standard rod.  Fairly regular oil changes.

So I think if abused (neglected and crap/low oil?) the bottom ends can go.  However, my motor shows (touch wood!) that if assembled correctly, standard rods and bearings are fine for a lightly tuned road engine.  I wouldn't want to change the CDI or remove the limiter- maybe that is the saving grace?

Ian, have you put a post on the Yahoo MZOG group- those guy seem to know their 660 motors.

Also, my 620 SRX (similar engine) has a standard rod, and its also good (tho maybe not at the end of the season!).  I am a bit more worried about this as it will easily go WAAAY into the red, unlike the standard engine, but will just go easy on the "loud handle" and try not to wreck it.  Its going back on the road come the end of the season hopefully.

Thats all, cheers for now.  Good luck matey, sounds like your running a bit lean on that of late.

a

[guest146]

Hi
You have me thinking  now. Its hard to beliver that MZ could make such a weak conrod. I have never worked on one of these but is it the Rotax engine? I have had engines where the gudgon pin is fixed in the conrod and turns in the piston and some that turn in both.  it seems unuasual that these should wipe out a con rod so quickly. It major if you having to replace this so often. Does it run on a bearing in the small end?

Ken

[Ian]

Hi Andy ,

I'm surprised that Slipstream put a high compression piston on a standard rod , Has it not been over bored ,+1mm +2mm ?
As it was Slipstream that told me that if my high compression piston was fitted to a standard rod it stands a good chance of snapping the rod !
If you wish you can read my post on MZ riders forum ,Wonky works at Slipstream.

http://www.mzriders.com/mz/viewtopic.php?t=1765

I haven't tried MZOG ,If I join any more forums I'll start getting mixed up ! I've been meaning to cut it down ,to many interests.

Hi Ken,
It's a Yamaha 660 engine not MZ ,There is no bearing in the small end ,Up until now I've never replaced a conrod in any bike engine.

Ian

[Steve H]

Odd, Assumming the piston is the same weight and the engine stays within the same rev limits, then the conrod is under the same load. Granted the engine will have a greater output but this will compress the rod, not stretch it and snap it. The SRX engine is a close relative to the 660 motor and from speaking to a guy who worked for a tuning company  in Holland the standard Yamaha conrod is strong enough for the stock rev-range but can stretch quite a bit if revved to hard. He had spent a lot of time on his works dyno and I was inclined to beleive what he was telling me.

[Ian]

If it's stretching and snapping ,wouldn't it take the valves out before snapping ? could be a few seconds earlier I suppose.
If it's being compressed ,couldn't it buckle before snapping ?

Sorry just thinking out aloud !

I really need to turn the PC off and spend more time in the garage ,
All this typing isn't good for me...........

[Steve H]

My understanding was that he knew how much the rod was stretching by the fact the piston was cleaning the carbon from the squish area. From memory he was running squish somewhere between 0.5 to 0.8mm. Valves should have more clearance than this.
I'm not clear how a worn little end would cause scoring in the bore. Ok it can allow the piston to rock. Looking around this type of seizure seems to be referred to as 'four corner seizure' and is associated with overheating.
http://www.kartingtechnic.dk/html/piston_seizure.html (Yes I know is for two strokes)
Whats your oil pump like ?. I seem to remember Steve Lake have a few siezures which were down to a duff oil pump

[bikeseamus]

Ian
         It looks like you're in luck, Buddy.

     Vesrah now makes a high performance connecting rod kit, and a dealer on ebay who ships WORLDWIDE is starting to sell them with opening bids at 84 USD, and it looks like it comes with a new crankpin, too.

  I like Vesrah stuff, and I'll bet this new kit will be stronger than stock.  Check out item # 130089953731.

    Hope this helps.        Jim
 

[andy230]

Hi Andy ,

I'm surprised that Slipstream put a high compression piston on a standard rod , Has it not been over bored ,+1mm +2mm ?
As it was Slipstream that told me that if my high compression piston was fitted to a standard rod it stands a good chance of snapping the rod !
If you wish you can read my post on MZ riders forum ,Wonky works at Slipstream.

http://www.mzriders.com/mz/viewtopic.php?t=1765

Hello Iain,

No overbore, just a standard size Hi comp (Arias?) piston.  I understand its probably better to have a better rod in there, but at least its a new rod. And if I were spending a grand or so on a motor, I'd probably put down about another 250 or 300 quid for a top spec rod, but I didn't get that option!

Just a cheap bike! 

I've spoken to the guy at slipstream quite a lot, and I agree with what he says.  Especially as it was built as a track bike.  But it was only trackdays and occaisional road use if needed, not a serious top spec 80bhp racer.  Also, I am keeping the rev limiter as stock, so am not too worried.

And if it goes pop, it goes pop.  And I'll put the wheels on the DR and make a supermoto!  The bike owes me nothing, and the cycle parts aren't brilliant anyway. 

But (touch wood) it'll be ok and keep getting me to work.  Noisily!

Re. Vesrah kit, in contrast to bikeseamus, i've never been that impressed.  Mind you I've only bought gaskets and fork selas, and maybe a twistgrip.  It always seemed a bit like typical pattern stuff to me- ie. ok but only ok.  Fine for a clutch cover gasket, not fine for a conrod!!

[bikeseamus]

  I've used Vesrah valves and clutches and gaskets and oil  filters forever, in everything.  They aim to hit the market with stuff at least as good as anyone else's, but at a smaller margin of profit.
    They have been the oem manufacturer of millions of stock components for every Japanese Maker, and will build to specifications for anyone.
                                        In 40 years, I have never seen a defective vesrah part of any description, and have used their gasket sets and valves and bearings for all kinds of engine rebuilds, since 1977.

  Since they have jumped into connecting rods, I'll bet they are the best to be had for the money, and if they say they are high performance, they will be stronger than stock ones.

   Every year I speak to the Vesrah People who come over from Japan to attend the International Dealers and Manufacturers show in Indy, and I'm impressed with their focus, knowledge, and enthusiasm for all the new stuff they are coming out with.
                            I have asked them about metallurgy, and their eyes light up like Christmas Trees.  They enjoy their jobs and are obviously well compensated and respected for their efforts, which indicates a well run company.

   Their company is based upon solid engineering instead of slick sales, and they will be in business until the World ends, and I'm glad of it.
              There may be some junky stuff in the bike world, and there are different markets to aim for. Some people want visual sculptures over practicality, like Ducati.  Some like to pretend their stuff is just naturally better, like BMW. Some like to make rare high end status symbols, like MV or Benelli or Ferrari in the car world. 

 All cool with me. 

       Ian wants a strong connecting rod for a reasonable sum, so I thought it might be a good idea to let him know Vesrah has put their dog into the hunt.
                                                    Vesrah won't risk their fine reputation by building junk. It will never happen.

  I'll bet you a case of the beer of your choice that the new heavy duty Raptor Rod they make is at least 10% stronger than a stocker and costs more than 10% less to buy.
 
    It may not be a Carrillo or a Hot Rod in strength, but it sure as hell will be better than a stocker.

       If Ian doesn't want to steam his MZ up to 80 rear wheel HP, and wants to put some money elsewhere, it is something for him to consider..... that's all.

   

[Ian]

Apologies for the delay in responding to your posts everyone but I typed most of this out the other night /early morning then hit refresh ,definitely time for bed when your doing things like that !

Hi Steve H ,
A very interesting article ,It cover all the symptoms perfectly .
Even if it's meant for 2 strokes.
Unfortunately I don't know the history of the engine and seeing the play in the little end ,that's where I pointed the finger !

All parts will be checked before re-building

Hi Andy,
It's probably the extra 2mm ?
Just that bit to much for the standard rod and maybe way to much for a used one.
Yes I have to agree with you on Slipstream.
I just don't agree with their Carrillo rod price as far as I can see there no excuse for a 140% extra for UK buyers !

Hi bikeseamus,
Thanks for the link to the Vesrah con rod.
But I'm not sure about putting a 102mm piston on top without somebody known for building 660 engines recommending it.
It would be fine in a standard engine though.
I've used Vesrah parts before never had any problems ,it's very tempting.

As for 80bhp I can get my self in enough trouble with a standard engine.
I only bought the one with the 102mm piston because it was the right price and I thought it would be a quick way of sorting the travellers engine problems out.
How wrong was I ?
It's turned in to a money pit and it is the first time in 17 years my other half has got really P off about my bikes.
In fact it's got so bad that I have thought about breaking the traveller for spares .
At the moment the two Skorpions are cowering in the corner at the back of the garage under tarpaulins having had their harts riped out.
One engine is on the floor and the other is on the work bench less than half way to having it's crank removed .

So far I've had 2 offers from the UK to fit con rods ,but they have not responded to emails as to who makes them.
I've just had an email from Barkersbar "yes we can ship them to the UK whenever you need them"
I think one of their rods will be finding it's way over this way.......The only problem left is finding someone to fit it.

[Ian]

I've just picked up a cheap bottom end ,it all looks in good condition.
This is going to be used to build a standard engine just to get a bike back on the road.

None of the people that said they could supply and fit a heavy duty con rod have got back to me or replied to my last lot of  emails ,Since I asked them who makes the con rods that their supplying .....thanks a bunch......

So running a 102mm piston is not going to happen for a while

I might leave the money pit till the winter........It all depends on my free time........