slight piston damage, opinions please

[rodbolt]

Re: slight piston damage, opinions please

the piston in the picture is absolute junk, note the groove between the piston crown and the first ring land.
I hope the next rebuilder is more careful than the first .
or simply part it out now while the crank,rods and block are still rebuild candidates.
please dont foist yet another "rebuilt engine" on ebay.

 

[bob johnson]

Re: slight piston damage, opinions please

the piston in the picture is absolute junk, note the groove between the piston crown and the first ring land.
I hope the next rebuilder is more careful than the first .
or simply part it out now while the crank,rods and block are still rebuild candidates.
please dont foist yet another "rebuilt engine" on ebay.

that is the exact reason for this thread... to find out if that groove is a BIG PROBLEM!!!

some people might do things on the sly, others might do the same thing out of ignorance, with no ill will.

I dont sell on ebay!!

thats two for a BIG NO_NO


anyone else on the NO WAY, reuse that piston band wagon..

be honest....

anyone want to buy some 1988 70 evinrude parts???

bob

 

[trendsetter240]

Re: slight piston damage, opinions please

anyone want to buy some 1988 70 evinrude parts???

I might be interested in the powerhead parts only. Anyone know if the 88 and 90 powerheads are the same?

 

[Faztbullet]

Re: slight piston damage, opinions please

Everthing will interchange but the crank.....

 

[trendsetter240]

Re: slight piston damage, opinions please

Everthing will interchange but the crank.....

Really? I have two a 1995 and a 1990. Both 70hp Evinrude. I know the cranks are different for the 1995 (fine spline) but are they also differnet for the 1990?

Bob PM me if you are interested in selling the powerhead.

 

[G DANE]

Re: slight piston damage, opinions please

Bob - wasnt the piston I found for you on ebay exactly same p/n NOS at 60 $ - look at my post, seems the same. If the other pistons are fine, that should be a fair solution imho.

 

[bob johnson]

Re: slight piston damage, opinions please

Bob - wasnt the piston I found for you on ebay exactly same p/n NOS at 60 $ - look at my post, seems the same. If the other pistons are fine, that should be a fair solution imho.

Ill have to do some cross referencing...mine are 3022P4

I can measure mine..if it mikes the same as the ebay ad....that is a big savings...about 50% off!! and brand new!!

thanks for the link.

bob

 

[Joe Reeves]

Re: slight piston damage, opinions please

Dhadleys' explanation pretty well nailed the cause of your present problem.

The cure..... replace that bottom piston and the cylinder head.

You're never going to get all of those metal particles (steel) out of the cylinder head. They will glow like a glow plug on a model airplane engine when that engine is running, resulting in pre-ignition, which in turn will result in a melted piston, damaged cylinder walls, etc. And since the cylinder is already bored oversize to .040, that will require a resleeving job.

 

[bob johnson]

Re: slight piston damage, opinions please

well i already fly cut the head.... looks usable to me....there is some pitting where the salt water ate away on the aluminum...but that isnt an issue with the compression.

bob

 

[a70eliminator]

Re: slight piston damage, opinions please

That looks good how much did you take off, I'll bet at least .060 to get those chew marks out, seems like it will effect compression enough to require either thicker gaskets or a custom pistons.
I started off with a reply the piston looked useable, guess that tells you what I know about outboard rebuilding.

 

[trendsetter240]

Re: slight piston damage, opinions please

That looks good how much did you take off, I'll bet at least .060 to get those chew marks out, seems like it will effect compression enough to require either thicker gaskets or a custom pistons.
I started off with a reply the piston looked useable, guess that tells you what I know about outboard rebuilding.

Interesting... I had the same sort of marks on my head, maybe not quite as bad as his. My machine shop took off .020 and soda blasted it. I didn't use a special gasket or pistons. Compression on mine is 135-139-136.

No problems so far.

 

[bob johnson]

Re: slight piston damage, opinions please

no way close to .060"!!!

i took maybe .010" , i would have liked to take a little more because of the corrosion spot, but i know that the compression might go up to an unreasonable pressure, especially since it is already .040" OVER!!!

plus i took maybe .005" off the deck of the block for a nice clean fit, and to cleanup some of the corrosion from the water passage edges.

I was actually THINKING about programming my CNC machine for recut the head inside, to alleviate any high spots in casting and to give a little more volume..

I may still do that..... Id would like to hear what people say about the compression rise in just the over .040 bore!!!

that alone should raise compression?? anyone got a guess on what a .040 for that size bore might do to compression???

bob

 

[trendsetter240]

Re: slight piston damage, opinions please

no way close to .060"!!!

I may still do that..... Id would like to hear what people say about the compression rise in just the over .040 bore!!!

that alone should raise compression?? anyone got a guess on what a .040 for that size bore might do to compression???

bob

Yes, check out my post above. #1 and #2 are .040 over and #3 is .030 over.

 

[bob johnson]

Re: slight piston damage, opinions please

Yes, check out my post above. #1 and #2 are .040 over and #3 is .030 over.

I checked all your posts, i didnt see one that mentioned a .040" over piston.

i saw one for .020" over.

did you get work done that resulted in different size bores on the same motor?

anyway...what was the compression on the .040" bore? and was it a lot different than the standard compression?


re read it...are you just adding info to your post and telling that 1 and 2 are .040" and 3 is .030" over?

is that a different motor than the one that was .020" over?

edit+ my bad i see the .020" applies to ther head material removal...SORRY!


bob

 

[trendsetter240]

Re: slight piston damage, opinions please

I checked all your posts, i didnt see one that mentioned a .040" over piston.

i saw one for .020" over.

did you get work done that resulted in different size bores on the same motor?

anyway...what was the compression on the .040" bore? and was it a lot different than the standard compression?

bob

My head had the same type of damage from a broken ring. My machine shop took .020 off the surface of the head and soda blasted it.

Two of the cylinders in my block were already .020 over before I went to rebuild it. Those two had to be bored out to .040. The last cylinder only had to go to .030.

I have the following readings after about 25hrs since rebuild.

#1 Cylinder - .040 135PSI
#2 Cylinder - .040 139PSI
#3 Cylinder - .030 136PSI

The pistons are Wiseco 3172 series. The engine is a 1995 Evinrude 70hp.

Hope that helps!

 

[bob johnson]

Re: slight piston damage, opinions please

My head had the same type of damage from a broken ring. My machine shop took .020 off the surface of the head and soda blasted it.

Two of the cylinders in my block were already .020 over before I went to rebuild it. Those two had to be bored out to .040. The last cylinder only had to go to .030.

I have the following readings after about 25hrs since rebuild.

#1 Cylinder - .040 135PSI
#2 Cylinder - .040 139PSI
#3 Cylinder - .030 136PSI

The pistons are Wiseco 3172 series. The engine is a 1995 Evinrude 70hp.

Hope that helps!

it does
and so does the anti brain dead pills i took a little while ago!!! ha ha

sorry again fior the confusion

but amazing that that extra volume isnt compressed into more compression!

bob

 

[Faztbullet]

Re: slight piston damage, opinions please

Bob you got to remember that you only increased bore size overall .020(20+20=40) and you have only added tenth's to CC volume. On a .040 bore you will see 1-3 psi increase and for ever .010 you cut on head you will deminish the combustion chamber about .7 CC's. You can cut the head up to .025 as gasket makes up about .040 when compressed and compression will not raise more than 3-5 psi with a .025 cut.

 

[bob johnson]

Re: slight piston damage, opinions please

thanks Fazt....

stored it...

now.....while i love doing stuff myself, i dont just do it to be cheap...BUT...

back to my piston....it is the fly in the ointment here... consensus is it could cause problems..

the groove on the side above the ring.

does anyone see a problem with me TIG welding that up and machining back to flush?

being a tool maker for a long long time, i have no doubt i could make it look like it was never there...and save $60 plus shipping..

will the slight difference between the filler rod and the forged piston aluminum, cause an issue?

cheapness aside of course!!!

I am actually looking forward to assembling this motor if i dont part it out...

except for all the carb linkage.....hope i can find all the pieces !! ha ha ha

and i dont relish all the bearings I have to buy for the LU rebuild...

lots of pitting there on most of the bearings.....

bob

 

[bob johnson]

Re: slight piston damage, opinions please

Bob - wasnt the piston I found for you on ebay exactly same p/n NOS at 60 $ - look at my post, seems the same. If the other pistons are fine, that should be a fair solution imho.

would you assume that the 3227KD on the box of that Ebay item means it comes with rings?

doesnt say so in the ad. I emailed him...but from his comments on other items he doesnt know a lot of what he has, he just bought out a big place and is selling it off.

the wiseco pistons i had thought about buying for $109 apiece come with wrist pins, c-clips and rings!!

bob

 

[bob johnson]

Re: slight piston damage, opinions please

bores are 3.229" dia

pistons on the skirt measured 90 degrees to pin are 3.221" dia

the retainer pins for the rings are solid, not rolled...

the ring gap.....019" goes .020" does not.

if i remember right , that is kinda high for a fresh rebuild..

but these rings have been used some at least..

my thought being that any new rebuild will do the same..once the rings seat...

does the ring gap cause me a lot of issues too???

bob