040 cast pistons 70hp

[dcr42t]

Does anyone know if cast pistons are available for a 49ci 70hp johnson in .040 oversize? Or do they only go to 030.

I know forged wisecos are available, but i dont want to use them.

Thanks

 

[emdsapmgr]

Re: 040 cast pistons 70hp

The factory only makes .040 over pistons for the V4/V6 crossflow product line. You'll have to look elsewhere. Someone can probably chime in with an alternative supplier of cast pistons.

 

[boobie]

Re: 040 cast pistons 70hp

What's wrong with wisecos ??

 

[multimech]

Re: 040 cast pistons 70hp

Wisecos are all right if the engine is bored correctly for them and a proper break is done. If you find it is your only option, find a machine shop that knows how to bore the engine for them. They are forged and react differently to heat than cast pistons. I think this is why to some people Wisecos get a bad name.

 

[durban]

Re: 040 cast pistons 70hp

uploaded are 2 pistons 1 origional omc piston more than 40 years in service , the other 1 has got a M or W stamp on the inside of it , either way i read it it looks the same to me so i dont know who its made by , iam no piston specialist , i do prefer the omc piston .
the wall thickness on the omc piston is thicker
the distance from the top ring to top of dome is greater
the omc piston being in use for more than 40 years the gugion pin does not move side to side or up & down play between the outside diameter of the pin & diameter of piston pin hole when i pull thr conrod up & down it did not move around , the other piston had exessive play in it the result was it knocked a hole in the block with the conrod due to that play in it .
it also apeared to me that it did not look very old the piston with the letter M or W stamp on , my con clusion i came to is that i will stick to OMC pistons , have a look at photos you will see the differances
the motor i stripped had all 3 pistons with the M or W letter stamp on the inside of the pistons , 2 of the pistons had play in the gudgion pin between gudgion piston hole & pin the other one had a broken skirt photo shown , so i think i will stay with omc pistons .

 

[Faztbullet]

Re: 040 cast pistons 70hp

Yes you can get 040 pistons from wsm...
Durban those are both omc factory pistons

 

[dcr42t]

Re: 040 cast pistons 70hp

Well thats good news. Was thinking i may have to resleeve back to 3". Thanks Faztbullet.

Another question
What size main jet for .040 over? I have heard 2 steps up in size from standard? So if i have a 52d, i go to 54d? Is this correct.

And on a 70hp, while i have the head off, will i gain much by shaving the head 1mm to raise the compression? I dont want to muck around with the ports etc.

 

[Chinewalker]

Re: 040 cast pistons 70hp

Durban - your pistons are from different motors of different years. They changed the design of the pistons in the 1970s from the high-ring pistons, moving the ring a little lower on the skirt so it would be less likely to break out a piece of the crown...

 

[Faztbullet]

Re: 040 cast pistons 70hp

+1 and the wristpins and rods are differents sizes also

 

[durban]

Re: 040 cast pistons 70hp

i dont think so cause my 1970 60hp distributor conversion motor to CDI has got the origional pistons in like the one in the photo with the top ring lower down from the dome & most of my other 70hp motors have the same pistons in as the 60hp my collection starts from 1970 to 1984 & all the 1970,s motors have the origional pistons in except this one i found on the scrap heap a few days ago it apeared to been have worked on before they obviously could,nt fix it & threw it away when i openened it up i found those 3 pistons in with the M or W stamp on it the motor is a 1973 70 hp , so some where along the line some one has changed pistons . or my pistons have been changed prior to me owning the motor , the piston design did change in about 1974\5 from what to what i dont know , how ever i prefer the one with the rings lower down

iam from the old school , & in those years things were made properly .......

 

[Chinewalker]

Re: 040 cast pistons 70hp

Any casting numbers inside your pistons?

 

[durban]

Re: 040 cast pistons 70hp

i have 2 pistons from a 1974\5 ,,70hp & 1 from a 1977 ,, 70hp , both with the thicker distance from top of ring to top dome & Yes they have factory cast numbers in the in side , the 3 with the M or W on have no numbers only arrows on the dome,s

 

[Faztbullet]

Re: 040 cast pistons 70hp

Shaving the head will not get you much maybe 1-3hp at best, use a 75hp head as combustion chamber is smaller. Jetting is correct as 2 sizes will be ok and prop engine near 5800rpm

 

[dcr42t]

Re: 040 cast pistons 70hp

Ah ok, i didnt realise the chambers were different. Thought it was just a shaved version.

I picked up some carbs with adjustable idle needles. They have 57c mains in them. I was told these came off a 70 but they have a 45degree nozzles? What year would these be off? Any ideas?



I checked my old carbs and they had 54d in them. Whats the difference with the lettering regarding the jets?

 

[dcr42t]

Re: 040 cast pistons 70hp

Ah ok, i didnt realise the chambers were different. Thought it was just a shaved version.

I picked up some carbs with adjustable idle needles. They have 57c mains in them. I was told these came off a 70 but they have a 45degree nozzles? What year would these be off? Any ideas?
View attachment 182106
View attachment 182107

I checked my old carbs and they had 54d in them. Whats the difference with the lettering regarding the jets?

 

[Faztbullet]

Re: 040 cast pistons 70hp

I checked my old carbs and they had 54d in them. Whats the difference with the lettering regarding the jets?

"D" is for looper motors and "C" is for crossflow motors...they are not for a 3 cylinder engine

 

[dcr42t]

Re: 040 cast pistons 70hp

"D" is for looper motors and "C" is for crossflow motors...they are not for a 3 cylinder engine

Will it cause any dramas with fuel delivery running C jets?
Any ideas about the 45 deg nozzle? Ive only seen flat nozzles on the johnsons ive had.

 

[Faztbullet]

Re: 040 cast pistons 70hp

Will it cause any dramas with fuel delivery running C jets?

The jet ID is different as is the chamfer between the 2 jets. For example a 56C jet might flow 10cc at 5 psi and a 56D might flow 20cc at 5 psi, that why they are labeled C and D