opinions on what to do about scratches inside piston wall

[apollothesun]

hope some of you gurus can help a newbie out. i have a 1977 evinrude 115hp model
115793. lost compression on piston 4. i tore it apart and the piston head was damaged. looks like the piston rings were hitting up at the cylinder head. ive since got a used cylinder head and was going to purchase a new piston but im not sure about some scratches where the exhaust port is. here are some pics





if you look closely, im concerned about the exhaust hole on the left.
these pistons are already .030 and looking at the parts manual, thats the biggest they come.
do you think honing the cylinder wall will do the trick or is this pretty much junk. please advise. thanks in advance.

 

[emdsapmgr]

Re: opinions on what to do about scratches inside piston wall

Possible that some of the apparent scratches may be delaminated aluminum that have deposited onto the cast iron cylinder liner. That can be cleaned off with some muratic acid and a swab. You can dissolve that aluminum if you do it carefully. Once you know the cyl is clean, you can hone it. After honing becomes the decision point. A singe scratch or two may be ok. If you still find that multiple, deep scratches are still evident up and down the bore-you are going to have to overbore it again. The issue is that exhaust gas will run down those small scratches, exposing the rings and piston skirts to hot exhaust gas. While an engine may run for a while, it will surely suffer a shorter life span-not be very durable over time. Though Bombardier does not make oversize pistons beyond .030, other manufacturers do. A couple of things to keep in mind: I'm not a fan of mixing pistons of different manufacurers in one powerhead. Often they have different expansion rates which can cause problems. (it's also possible they may not weigh the same as the factory pistons.) Also, when you start to get beyond the .030 oversize, you may need to jet that one carb throat up somewhat to compensate for the one larger piston size. It is acceptable to overbore just one cyl in a powerhead. When the ring let go, it typically damages the head. You are doing the right thing to replace the old head. The (old) head pits can cause hot spots and minute pcs of the rings may imbed themselves in the head face, which can later come loose.

 

[kenmyfam]

Re: opinions on what to do about scratches inside piston wall

Do you have a photo of the head you took off ???

 

[wilde1j]

Re: opinions on what to do about scratches inside piston wall

If the grooves are deep enough, I would consider having a new liner installed in that hole (not a DYI job). You need to determine why that cylinder failed, or it will happen again.

 

[apollothesun]

Re: opinions on what to do about scratches inside piston wall

Possible that some of the apparent scratches may be delaminated aluminum that have deposited onto the cast iron cylinder liner. That can be cleaned off with some muratic acid and a swab. You can dissolve that aluminum if you do it carefully. Once you know the cyl is clean, you can hone it. After honing becomes the decision point. A singe scratch or two may be ok. If you still find that multiple, deep scratches are still evident up and down the bore-you are going to have to overbore it again. The issue is that exhaust gas will run down those small scratches, exposing the rings and piston skirts to hot exhaust gas. While an engine may run for a while, it will surely suffer a shorter life span-not be very durable over time. Though Bombardier does not make oversize pistons beyond .030, other manufacturers do. A couple of things to keep in mind: I'm not a fan of mixing pistons of different manufacurers in one powerhead. Often they have different expansion rates which can cause problems. (it's also possible they may not weigh the same as the factory pistons.) Also, when you start to get beyond the .030 oversize, you may need to jet that one carb throat up somewhat to compensate for the one larger piston size. It is acceptable to overbore just one cyl in a powerhead. When the ring let go, it typically damages th head. You are doing the right thing to replace the old head. The (old) head pits can cause hot spots and minute pcs of the rings may imbed themselves in the head face, which can later come loose.

thanks for the reply. i appreciate your insight.
there really isnt any deep scratches on the wall when a run my fingers on the inside of the piston chamber wall, almost non-existence. but the one thing i do feel is where the left exhaust hole there is an indentation i can feel with my hands. do you think i can smooth it down with muratic acid and then hone it down? i really like this idea. any pointers in how to do this with the cotton swab?
if i do overbore it to .040, any suggestions of which piston i should go with and a estimated cost of doing this so i now an idea if i bring it in a marine shop. if i do overbore, would it effect the cylinder head fit?
i got this boat for real cheap and this is the reason why, im not to sure if i want to put more money in it then i have too.
i will weigh my thoughts on your suggestions.

 

[apollothesun]

Re: opinions on what to do about scratches inside piston wall

Do you have a photo of the head you took off ???

yes i do, noticed the one side on it. i believe it started to hit the exhaust hole when the rings gave way

 

[apollothesun]

Re: opinions on what to do about scratches inside piston wall


im surprised it didnt do alot of damage inside the piston wall

 

[apollothesun]

Re: opinions on what to do about scratches inside piston wall

If the grooves are deep enough, I would consider having a new liner installed in that hole (not a DYI job). You need to determine why that cylinder failed, or it will happen again.

thanks for the info. is having a new liner expensive to do at a marine shop?
i believe the resason this happened was that this was ran in saltwater and flushing wasnt done properly. there was a blockage on the cylinder head where water would not enter causing overheating. while pulling the powerhead off, alot of salt corrosion was present.

this is my deliemma,
i already have a boat and this was my project winter boat. i want to get this boat up and running use it for a while then turn around and sell it. i will disclose all that happened in this boat and i noticed now i will not get alot out of it due to costs and time i put into this. im adding a kicker bracket and motor just for backup due to this. your thoughts and suggestions are welcomed here.
thanks
apollo

 

[wilde1j]

Re: opinions on what to do about scratches inside piston wall

Replacing one liner is around $350 plus shipping for liner and labor. The reason it's so costly is your block has a cast in place liner, and it's one of the more labor intensive liners to replace. After measuring the bore carefully , both for diameter and roundness, you may also want to consider an aftermarket OS piston, such as Wiseco, who make pistons up to .064" oversize. Have the machine work done by a quality marine machine shop, like MarFab. From the looks of the hole, I don't think honing will be a practical choice. I wouldn't be too concerned about piston weight difference. If the head has metal embedded or deep nicks, look to get a used cylinder head.

Jet size doesn't change BC of overbore.

 

[DargelJohn]

Re: opinions on what to do about scratches inside piston wall

I agree with Jim. I recently bored a 88 SPL block from .030 to .040, and used aftermarket piston kits. Works great.

 

[bob johnson]

Re: opinions on what to do about scratches inside piston wall

Dont want to be a pain, but you people need to focus the camera when you take pictures....the nature of the question relies heavily on the picture, and the picture needs to be clear and sharp to even have a chance of helping...a blurring picture just gives a headache and doesnt nothing to help....to answer your question requires a good view of the scratches you mention..and even with a GRAT picture it is possible a person cant say one way or the other if they are too deep...

the depth and length is relevant!!!!!!!!!!!!!!

you might be able to hone and buy slightly larger new rings.... there is a tolerance for roundness and dia, you need to check those as well...

there is a lot of damage in the cylinder wall!!! you dont need much to less pressure escape!!!!

for piston and bore fit, there is little room...we are talking thousands of an inch....if you can catch the scratch with a finger nail it is SEVERAL THOUSANDS of an inch deep!!!!sooo to clean up a scratch .003" deep you have to removed .006" for the ID!!!! you are now out of spec for a new piston!!! you have to go and bore the hole and buy an oversize piston..


motors run for as long as they because attention to detail and close tolerances are held during manufacture or rebuild,.......


you can throw a piston in and get by fine maybe ......if you boat in warm weather, in calm waters with lots of people around....you got few worries.. if you boat rough seas far from shore...you want a reliable motor!

good luck

bob

 

[apollothesun]

Re: opinions on what to do about scratches inside piston wall

Dont want to be a pain, but you people need to focus the camera when you take pictures....the nature of the question relies heavily on the picture, and the picture needs to be clear and sharp to even have a chance of helping...a blurring picture just gives a headache and doesnt nothing to help....to answer your question requires a good view of the scratches you mention..and even with a GRAT picture it is possible a person cant say one way or the other if they are too deep...

the depth and length is relevant!!!!!!!!!!!!!!

you might be able to hone and buy slightly larger new rings.... there is a tolerance for roundness and dia, you need to check those as well...

there is a lot of damage in the cylinder wall!!! you dont need much to less pressure escape!!!!

for piston and bore fit, there is little room...we are talking thousands of an inch....if you can catch the scratch with a finger nail it is SEVERAL THOUSANDS of an inch deep!!!!sooo to clean up a scratch .003" deep you have to removed .006" for the ID!!!! you are now out of spec for a new piston!!! you have to go and bore the hole and buy an oversize piston..


motors run for as long as they because attention to detail and close tolerances are held during manufacture or rebuild,.......


you can throw a piston in and get by fine maybe ......if you boat in warm weather, in calm waters with lots of people around....you got few worries.. if you boat rough seas far from shore...you want a reliable motor!

good luck

bob

thanks for chiming in Bob,
i will take better pictures tonight. i will get something to reference it so you can see the depth.
i think i posted the thread wrong,
i shouldve posted as "exhaust port scuffed inside cylinder, opinions needed"
i assure everyone that the cylinder has no grooves or hard scratches, nothing honing will fix. im not to sure if honing will smooth the exhaust port scuff though, so i may need to re-bore.

its the exhaust port hole that has the real issue.

 

[apollothesun]

Re: opinions on what to do about scratches inside piston wall

Replacing one liner is around $350 plus shipping for liner and labor. The reason it's so costly is your block has a cast in place liner, and it's one of the more labor intensive liners to replace. After measuring the bore carefully , both for diameter and roundness, you may also want to consider an aftermarket OS piston, such as Wiseco, who make pistons up to .064" oversize. Have the machine work done by a quality marine machine shop, like MarFab. From the looks of the hole, I don't think honing will be a practical choice. I wouldn't be too concerned about piston weight difference. If the head has metal embedded or deep nicks, look to get a used cylinder head.

Jet size doesn't change BC of overbore.

hey Jim, thanks for getting back to me, i already got the cylinder head off of ebay and should be here this weekend.
i will try to get the powerhead to a shop in the next couple days to try to get a quote. maybe calling around first.

 

[apollothesun]

Re: opinions on what to do about scratches inside piston wall

i still like the muratic acid idea with the cotton swab. if i can just smooth that exhaust port hole all will be good in my opinion.

 

[apollothesun]

Re: opinions on what to do about scratches inside piston wall

I agree with Jim. I recently bored a 88 SPL block from .030 to .040, and used aftermarket piston kits. Works great.

im gonna call around today and see if i can get a quote, thanks for chiming in

 

[kenmyfam]

Re: opinions on what to do about scratches inside piston wall

yes i do, noticed the one side on it. i believe it started to hit the exhaust hole when the rings gave way

I was asking for a photo of the head if you have one.

 

[wilde1j]

Re: opinions on what to do about scratches inside piston wall

Have you ever used muriatic acid? The stuff will destroy a swab in seconds. A neighbor used it to remove stains from his concrete driveway ... the brush he was using to spread it lasted about two minutes. Nylon and similar materials are the only common materials which survive this stuff. Use long neoprene gloves and safety glasses as minimum protection.

 

[Jayrock]

Re: opinions on what to do about scratches inside piston wall

I have done the Muriatic acid trick to remove melted aluminum from cylinders before. On Motorcycles as well as smaller outboards. First off, Make sure that the cylinder taper is well within specs, and is also within spec for the new piston. If all is good, then its possible to do this without going in to the machine shop. Secondly, you need a face shield or really good safety glasses, and a Vapor respirator. The fumes from That acid will literally knock you out or even burn your sinuses. To do this, realize that the acid does not care what aluminum it eats away. It will destroy good metal too. So, to do only one hole and not affect the other cylinder/s is very difficult. The reason is, you need to have a way to neutralize any acid that pools in the bottom of the cylinder, while you are swabbing the affected areas. Also, any grit and metal shavings CANNOT get into any of the other cylinders at all! To keep excess acid from eating good metal, I use a spray bottle with water, and a little baking soda mixed in. Make sure the engine is in a position that any fluid running out of the cylinder bottom, does not trickle into one of the good cylinders. I have used regular old Q-Tips dipped in Acid to swab the affected area. They dont last long, but you dont really need them too. You will know when you have all the aluminum off the wall when it doesn't foam up any more. Once all the built up aluminum is removed you will have a better Idea what the damage is. If the scratches are not deep enough to feel with a finger nail, you are probably good. Now hone the cylinder. When the proper hone is achieved, remember to chamfer the edges of ALL the ports. I use a dremel and a ball hone. If you don't do this the new rings could catch on the port, and cause the same damage again. As far as a chip or scratch in the port, try to blend it evenly accross. If the chip is real big, then you need a new liner. period. When finished, CLEAN, CLEAN AND CLEAN AGAIN! This is why tryin to be sneaky and only do one cylinder is tricky. I would completely disassamble the motor, Mic all the cylinders, Clean them all up, hone them, Without the fear of getting junk into the other cylinders. Also re-ringing those other pistons is a cheap way to improve performance and longevity. You have the engine apart now, Why not? You will be happy you did...

 

[kenmyfam]

Re: opinions on what to do about scratches inside piston wall

Nice information Jayrock.

 

[apollothesun]

Re: opinions on what to do about scratches inside piston wall

hey Jayrock,
after reading your post you enlightened me to break the powerhead down completely.
im glad i did too, piston 1 and 2 rings were broken also, probably from debri from
piston 4. upon looking and feeling around at the piston 4 wall, im gonna have to rebore to a bigger piston. the scratches on the wall can be felt with my finger nail. all the other piston walls are good just need some honing to do.
alot of carbon gunk inside the exhaust housing that i proceeded to clean. theres a machine shop that works on marine motors closeby. i will bring the powerhead to them and have them examine the piston wall.
one bummer is i cant find one of those small roller bearing. i searched everywhere for it. im hoping i can still buy those still.