slight piston damage, opinions please

[bob johnson]

I picked this 1988 70 hp up last year about this time..one thing led to another and i eventually dissasembled it...not wanting to be so close to repairing or replacing something while I had it THAT FAR apart and not take care of it...which led to me TOTALY taking it apart!!

what i found was what looks like a FRESH rebuild with .040" over pistons.

BUT it appears that something let go and was smashed between the head and piston on the bottom cylinder...

but then they just replaced what ever broke and reassembled the motor!

i checked and ALL needle bearings are accounted for and the rings looked brand new.. the pins that keep the rings from rotating are in place.. the crank bearings are all in their races...

the pistons had ZERO carburization...super super clean...same for the rods...

with the exception of the hammering top and a few marks ON THE SIDE of the bottom piston..

I have had the block boiled and honed...he took out less than .0005"!!!

the block measure right for a .040 over bore..the pistons are marked .040.. and measure right.. have no skirt wear

here is the damage

i have since fly cut the top of the head .005" to clean it up!

here is the block post hone..just a few small places that stayed dark, i told him to just give me a surface to set the rings( in case i use brand new ones)

this picture shows just how the piston looked when it came out of the motor..seems pretty dang clean!!!

here is a pix of the side of the suspect piston

here is a picture of the slight drag mark from a piece of debris on the side of the piston above the ring grooves..which is y main question for this thread

will these slight grooves on the SIDE of the piston cause me problems, If i just reassemble this motor?

I will probably sell this motor, because since it bought it and took it apart i have aquired other motors to use for its intended purpose.

I have no notion to defraud anyone, buit i want to keep my costs of rebuilding this motor down!!!. it is tottally cleaned and painted..and ready for reasembly if I can come to grips with this piston issue.

I mean i took EVERY bolt off this thing and sand blasted every housing part and primed with antifouling primer and painted with Evinrude blue!!

I would add that the compression numbers were 115 120 and 120 when i bought the motor...

bob

 

[bob johnson]

Re: slight piston damage, opinions please

here is another good picture of the side of the suspect piston...it came out of the motor just like this...very clean...but slightly damaged...

which i really believe happened prior to its last assembly

does anyone thing these marks on the side will cause me problems???

i am conserned about the marks between the top of the piston and the ring grooves basically


bob

 

[a70eliminator]

Re: slight piston damage, opinions please

I would say the marks are are superficial to the operation of the piston.

 

[1946Zephyr]

Re: slight piston damage, opinions please

it looks like a good candidate for replacement, but only thing is, you'll have to replace all three as a set. Unless of course you find someone who will sell you a single. It looks like something banged around in the combustion chamber for a while.

 

[samo_ott]

Re: slight piston damage, opinions please

If it was me, I'd reuse it, but you have done so much work, why stop now?

 

[rolmops]

Re: slight piston damage, opinions please

It may not be crucial for the engine today but,the the damage on the one side of the piston will cause the pressure of the igniting fuel to enlarge the damage and a few years down the line somebody will get stuck in the middle of the lake.
If I were to keep the engine I would resleeve and go back to the original size.If I were to sell I would replace the damaged piston just to do what I would like to have done to me.

 

[Dhadley]

Re: slight piston damage, opinions please

Seen this too many times. The damage is probably from a broken ring.

Here's the typical scenario - a ring breaks, block gets bored to .040 (or whatever it takes to clean up) and goes back together. Rebuilder doesn't replace the head (cheap way out). Doesn't take the intake apart to clean (cheap / lazy / easy way out). Installs new pistons, fires up motor. The small pieces of broken ring that were trapped behind the reed plate come out almost right away and damage the new piston. Now you have imprints of a broken ring in the head but no broken ring. Those same small pieces mark up the new pistons.

 

[trendsetter240]

Re: slight piston damage, opinions please

Looks pretty clean even for a newly rebuilt engine. Why did you take it apart if there was good compression? Was there any sign of water intrusion rust etc?

The pistons are Wiseco forged pistons btw, you can order a single replacement piston with the number stamped on the head of the piston.

And yes, I would replace it.

 

[trendsetter240]

Re: slight piston damage, opinions please

Seen this too many times. The damage is probably from a broken ring.

Here's the typical scenario - a ring breaks, block gets bored to .040 (or whatever it takes to clean up) and goes back together. Rebuilder doesn't replace the head (cheap way out). Doesn't take the intake apart to clean (cheap / lazy / easy way out). Installs new pistons, fires up motor. The small pieces of broken ring that were trapped behind the reed plate come out almost right away and damage the new piston. Now you have imprints of a broken ring in the head but no broken ring. Those same small pieces mark up the new pistons.

I think dhadley nailed it. This is exactly what happend to me; I bought a 1995 70hp with a head that looked just like that and one fried piston. Also looked like a recent rebuild at .020 and none of the rings were broken. I only paid 200 bucks for it though and knew what I was getting.

Clean up the head, replace the piston and rebuild it properly. My rebuilt 70 runs like brand new

 

[Faztbullet]

Re: slight piston damage, opinions please

Clean everything up and install 3 new pistons..the pic of 1st piston is "old stock" Wiseco as the piston # has changed, all newer Wiseco pistons start with a 31xx part nimber. I myself would "trash" the pistons as to much damage for my standards and if the block has "dark areas" around ports and upper cylinders after honing , motor has a lot more hours than you think. Re-mike the cylinders and they should be 3.227-3.230, remember the "skirt" is the life of the motor(it is almost bore size) and I agree 100% with Dhadley on lazy rebuilders.

 

[Faztbullet]

Re: slight piston damage, opinions please

Clean everything up and install 3 new pistons..the pic of 1st piston is "old stock" Wiseco as the piston # has changed, all newer Wiseco pistons start with a 31xx part nimber. I myself would "trash" the pistons as to much damage for my standards and if the block has "dark areas" around ports and upper cylinders after honing , motor has a lot more hours than you think. Re-mike the cylinders and they should be 3.227-3.230 , remember the "skirt" is the life of the motor(it is almost bore size) and I agree 100% with Dhadley on lazy rebuilders.

 

[Dhadley]

Re: slight piston damage, opinions please

Yes, those are very old pistons. Wasn't going to mention that because I agree they need to be replaced anyway. Those pistons were discontinued back in the late 80s. The number was then changed from 3022 to 3072. Then about 2001 or so it was 3172. Several changes other than just the Electra coating.

 

[1946Zephyr]

Re: slight piston damage, opinions please

I would also dip the block to strip everything off of it and make sure it is spotless. Give it a new coat of primer and paint. If this block is clean enough to eat off of, then it's less likely to suffer any more internal damage like what is shown in the above pics.

Faztbullet is right on. Get new pistons. Dhadley and I agree about lazy rebuilders. I tend to go further with a rebuild than most. I once had a lazy rebuild bite me in the ***. Never again.

That almost looks like the engine block out of my Geo Metro

 

[G DANE]

Re: slight piston damage, opinions please

If the other 2 pistons are intact, now and then you can find one similar with a little phone work around to rebuilders, or on ebay if you are lucky. I think the head is reuseable, dont grind the tops of, use a slightly rounded punch and carefully tap every little top the piece of ring has created around the hit marks, back to original surface. Only small groves are left, then.
There you go http://cgi.ebay.com/ebaymotors/NEW-...at_Parts_Accessories_Gear?hash=item3a55d2867c

 

[kenmyfam]

Re: slight piston damage, opinions please

I agree about the "cheap and cheerful" repair that was done. No cares about how it is down the road so to speak.

 

[bob johnson]

Re: slight piston damage, opinions please

well once i got the motor and found this site, and read i shouldnt run the motor until i rebuiuld the carbs and replace the water pump... thats what i took apart first!!!

compression was very good.

took the carbs off and had them rebuilt... took the LU off and apart.

then started to "check everything....because i was THERE!!

one thing led to another and I said let me pop the heads and take a look!!

I have flycut the head already and removed the marks.

the other pistons are in great shape

the MOST, i will do it replace the ONE piston and all three sets of rings.

but i would hoping to hear that since the compression was good, that the marks in the piston wont cause me grief!!

I still may just reassemble with the parts i have and just have disclosure..and price accordingly..

this motor will look GREAT...and it should run GREAT... Ill lose all my time, but i should at least get back my $700....

if it was a 90 HP, id keep it as a back up...

I can show all the work i have done in photos...once they see the extent i took this motor apart and how i sand blasted everything and primered and painted...they will know what they have...

the block has been decks slightly because there was a slight low spot outside the water jacket.

the block was bloiled and honed and primed and painted.....

the pistons mike up JUST barely in spec for the bore... they are like brand new

if the motor has a lot of miles on the bore it had when i got it, then they replaced .040 over pistons with .040 over pistons!!!

i dont care how old they are, they might have been on some rebuilders shelf for years...

thanks
for the info

bob

 

[trendsetter240]

Re: slight piston damage, opinions please

I still may just reassemble with the parts i have and just have disclosure..and price accordingly..

this motor will look GREAT...and it should run GREAT... Ill lose all my time, but i should at least get back my $700...

Hi Bob, I don't understand the logic after all the effort you have put in already. Why not just replace the one piston, all new rings and a powerhead gasket set? If you do that the motor will be worth twice what you put into it.

 

[Faztbullet]

Re: slight piston damage, opinions please

The older Wiseco pistons had problem with the ring locating pin falling/backing out as it was not a solid pin but a spring rolled pin, the newer piston have solid pins.

if the motor has a lot of miles on the bore it had when i got it, then they replaced .040 over pistons with .040 over pistons!!!

This is highly likely as someone may have been just trying fix it as cheap as possible. Any time you have dark areas around ports or cylinder top after honing that is a low spot due to wear and proper honing to remove them just enlarges bore. If pistons are barely in spec's(3.225) and bore is more than .003 over spec the pistons will slap till engine warms up...

 

[ENSIGN]

Re: slight piston damage, opinions please

You've goning through all this work so far so why start doing it half @$$ now.

 

[bob johnson]

Re: slight piston damage, opinions please

well one reason is I lost all my overtime last summer and have not got it back...thats about $1800 a month!!

I had it for 13 years straight..and got used to it. so now i have to watch what I spend money on...

I bought the 70 last feb, but then went and bought a 1997 90 with a slight knock for another $700, hoping it would be something easy as the guy took it for 14 trips, all dayers, all the while it had a knock( came on a boat he liked)

wife told him to sell it and get a new motor, because she was affraid of getting stuck....I mounted the motor and it ran great but the knock was deeper than i hoped and I got cold feet , so i bought a 1995 115( same weight) for $2500 and it runs great... sooooo i have invested a bunch of money in these motors...the 90 is the exact same model as the 115...so i got a nice parts motor in an emergency..

I d like to unload some stuff....but i dont want to invest more cash...


I might do the new piston and rings...thats about $175 i guess and the gasket kit...

plus all the new bolts i will need..

i could end up putting $400 into this motor ...not something Id like to do...

I cant sell the LU off, because the drive shaft wore the teeth( 4) in the crank...I welded up the drive shaft spline and machine back to fit the over size crank very nicely...so no slop

but it would'nt be a good canidate for another motor.. and to replace the drive shaft would be a lot of money..

If I had heard LOTS of people tell me that using the piston with the scratch in the side would cause PROBLEMS sooner than later....I might feel different about just putting the motor back together....

thanks for the replies

bob