Contra Horrors

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Update 1.

I have found a suitable crank and con-rod for not a lot. I have questions out to my bearing supplier, and a full replacement set looks possible, again, for not a lot of money. So far so good. I could get the crank re-ground - but it would be a lot more expensive than a good second hand one.

The bit that is causing trouble is the piston. I was always under the impression that 070 pistons and Contra pistons were interchangeable. Well, after a few minutes with the capliers, I can confirm that the only dimensions they share are the bore (58mm) and the wrist pin diameter. The compression height (centre of wrist pin to top of piston is about 7mm too big on the 070, so if I fitted that to the Contra, it would smash through the top of the jug.

So where do I get Contra pistons from? I know where to get 66mm Contra-S pistons (I've got some....), but I don't have 58mm Contras. Would an 075/076 piston work? I've never seen one, so I have no idea of the dimensions. Any suggestions gratefully received...!

Assembled company? Is that like Y'all.

:ices_rofl:

Belgian - thanks for the IPL, very useful!
 
Update 1.

I have found a suitable crank and con-rod for not a lot. I have questions out to my bearing supplier, and a full replacement set looks possible, again, for not a lot of money. So far so good. I could get the crank re-ground - but it would be a lot more expensive than a good second hand one.

The bit that is causing trouble is the piston. I was always under the impression that 070 pistons and Contra pistons were interchangeable. Well, after a few minutes with the capliers, I can confirm that the only dimensions they share are the bore (58mm) and the wrist pin diameter. The compression height (centre of wrist pin to top of piston is about 7mm too big on the 070, so if I fitted that to the Contra, it would smash through the top of the jug.

So where do I get Contra pistons from? I know where to get 66mm Contra-S pistons (I've got some....), but I don't have 58mm Contras. Would an 075/076 piston work? I've never seen one, so I have no idea of the dimensions. Any suggestions gratefully received...!



:ices_rofl:

Belgian - thanks for the IPL, very useful!
OK, happen to have an 076 piston on my desk right now - no calipers but I'll give you some ballpark measurements with a ruler for the moment. I can calliper it sometime soon. Gimme a sec I'll post it with a photo too...
 
Real time Q&A - gotta love the internet!

Here they are side by side:

attachment.php


NOS 070 on the left, Contra on the right. Both are Mahle.

The dimension in red on the left is 23mm, on the right is 15.5mm (roughly). Wrist pin is 15mm on both.
 
Real time Q&A - gotta love the internet!

Here they are side by side:

NOS 070 on the left, Contra on the right. Both are Mahle.

The dimension in red on the left is 23mm, on the right is 15.5mm (roughly). Wrist pin is 15mm on both.
uh oh, I'll post anyway in case anyone else wants to know, but it's not going to fit - sorry to be the bringer of bad news! Also ignore the POS camera...

attachment.php

a=53mm
b=25
c=4
d=3.5
wristpin = 13.5
rings = 1.5
 
Thanks Harry....it was a bit of a long shot. The 070 kit wouldn't fit the Contra - well it would fit the crankcase, but you wouldn't get the cover on the saw. The plug is in a different position on the Contra.

Does anyone know if Stihl dealers can get these? Yes, I'm willing to pay retail and I need several of them.... :dizzy:
 
Last edited:
Thanks Harry....it was a bit of a long shot. The 070 kit wouldn't fit the Contra - well it would fit the crankcase, but you wouldn't get the cover on the saw. The plug is in a different position on the Contra.

Does anyone know if Stihl dealers can get these? Yes, I'm willing to pay retail and I need several of them.... :dizzy:
right, I was assuming a full 070 conversion I guess...
Woa, you're really splashing for this! I'd assume they don't do contra pistons anymore - at least they still make the 070 and 090, but they stoppped the contra a while back. Wouldn't stop you trying though.

On a rather depressing side note, I went to the local dealer a couple of days ago for 075 and 041 parts. Got them all no worries but the old bloke said in passing that stihl very recently scrapped (crushed) a HUGE load of old parts, and are seriously stepping down old saw parts... Very upsetting I find when manufacturers stop supporting old products. But I guess they're just trying to make money, and those parts are insignificant. It may make financial sense, but it's still depressing.
 
It isn't that easy to get a "through hardness" on a metal. If the crank were to be hardened to say a 60 (the average knife blade is 70-76) it would still have a reasonable amount of flex but the bearing surfaces would wear down rather quickly. If it was hardened to a 70+ it would become brittle with little flex and eventually crack. So most cranks are hardened to around 55-65 then particular wear areas are surface hardened or chromed to withstand the constant wear. If you try and cut a crank in half the initial cut will eat a saw blade immediately because of the hard "outer shell" once you are past the shell it cuts just like any other cast iron, fairly easy generating almost dustlike shavings.
 
Actually everything was going quite well with the English language until we started letting the rest of the world play with it!

Yes I know. Thats why people don't use a fake New York or Southern accent to sound intelligent. They use a fake British accent.
 
I found a place that will make custom pistons and rings.

What do you reckon it would cost? If these are really hard to find, I'll bet there are some other Contra owners out there who might put in an order...
 
What do you reckon it would cost? If these are really hard to find, I'll bet there are some other Contra owners out there who might put in an order...

I might be one of them, I would need to buy a Contra first though! :clap: :chainsaw: :greenchainsaw:

Just have to keep watching eBay! :popcorn:
 
Small update.

Here are the stripped and sandblasted parts getting close to the masking tape stage. I've used plastic sheet for the big holes, and silicone tube to mask threads:

attachment.php


Brad, if you read this, you'll note there is an 07S crankcase there as well!

Got a crank and con-rod. Still can't find a piston. The guys at Otto engine works don't reply to email, I've got a few other requests to various companies.
 
Still can't find a piston. The guys at Otto engine works don't reply to email, I've got a few other requests to various companies.

RXE, it must be intensely frustrating, to not be 100% confident you'll have the parts for the rebuild, but I was able to find several companies that will make pistons to the customers specifications simply by entering "custom pistons" in either Google or Yahoo search. I am sure this is what you did, so with a few more Contra saws needing pistons and rings, it could bring the price down substantially from a one-off.

Best of luck.
 
Yep, I've tried googling.....!

JE Pistons - don't do two stroke
Otto - don't answer email
Arias - no reply yet

Any others gratefully received!

What happens if you put a 7-8mm spacer under the cylinder and use the 070 piston?

Unfortunately, the cover wouldn't fit on top of the saw if you did that!
 
Small update.

Here are the stripped and sandblasted parts getting close to the masking tape stage. I've used plastic sheet for the big holes, and silicone tube to mask threads:

attachment.php


Brad, if you read this, you'll note there is an 07S crankcase there as well!

Got a crank and con-rod. Still can't find a piston. The guys at Otto engine works don't reply to email, I've got a few other requests to various companies.

Sure thing. What are you painting them with?
 

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