Oh no! Ive done a bad thing :( need machining advice.

[jaykibo]

Hi everyone,

I've accidentally damaged the mating surfaces of the head and block on my Evinrude 115hp 1978 model (model number 115893C). :facepalm:
There are small scratches on the surface which is causing the head gasket to leak. I tried sanding it back with fine sand paper (starting at 320 and finishing with 400 grit) but I dont think this is something I could take out sanding it by hand. I know I need to get this machined (plus I would feel much better if I get it done properly by machining it).

Now the problem is, I really REALLY dont want to go through the hassle of pulling the block apart to get it machined. Is there ANY way at all that I can get a machines, smooth, flat surface without taking the engine apart?

The parts that im talking about are in the picture below.
The head (circled in blue) is fine to be send to the machinist.
The block (circled in red) is what I dont want to pull apart..

http://i.imgur.com/BAxtL6x.png

 

[jaykibo]

Re: Oh no! Ive done a bad thing need machining advice.

Some research on the net has revealed that I may be able to get within the tolerances if I use a piece of glass and sandpaper, paying extra attention to keeping the glass flat. I do this on the block.
As for the head, I get that professionally machined.

Has anyone done something similar to this and gotten away with it?

The thing is, I would much prefer to pull the think apart, but its an old engine and its really not worth the cost. If I can get another couple of years out of it I would love that. If it turns out I have to pull it apart then im just going to scrap the poor soul.

 

[duped]

Re: Oh no! Ive done a bad thing need machining advice.

I don't know how deep of a scratch you're dealing with, but for cleaning up surfaces like that, I like to use honing/polishing stones. They come in boxes of assorted grits and you can use the longer pieces to go across the whole surface to keep everything even and level.

 

[daselbee]

Re: Oh no! Ive done a bad thing need machining advice.

I sure would like to see a pic of the damage. Is it leaking water or compression? Where are these scratches? That should be an open deck crossflow, and if these scratches are in an area where the temps stay at 140 (normal operating temp), you can fill them with Devcon Liquid Aluminum, and smooth down by hand with sandpaper. I have done it, it works fine.

 

[jaykibo]

Re: Oh no! Ive done a bad thing need machining advice.

SUCCESS!

For posterity and to wrap this thread up ill just explain what I did along with a few pictures.

I borrowed a piece of glass from a picture frame and stuck it to 120 grit wet'n'dry sandpaper. I then stuck the other side of the glass to a piece of MDF I had lying around and screwed a crude handle to the back. You can see the result in the pictures.
I spend about 20 minutes sanding the block and head with the sandpaper and then changed to 400 grit, spend about 15 minutes using that and then finally changed to 1000 grit and spent another 15 minutes using that.
I used mostly circular motions and in both directions. At first I used up and down and side to side motions, but the circular seemed to be best.
I sprayed WD40 to get it to glide nicely and would frequently spray the paper and surface to remove any shavings and clean the paper up.

You cant really see the scratches in the pictures (sorry, I used my phone camera and it didnt come out too well) but before the work I was getting droplets of water on the spark plug when I would remove to inspect it from the bottom cylinder and the top of the top cylinder would leak water outside. Compression in both cylinders was about 125psi. Luckily, I didnt run it very long in this condition so I doubt I damaged anything inside.
After the job was done I am getting 135psi per cylinder and no more leaks (that I can detect). Both cylinders are firing nicely and no outside water leaks too).

BEFORE
http://i.imgur.com/qPkMXZD.jpg
http://i.imgur.com/G0sESk4.jpg
http://i.imgur.com/akJa73l.jpg

PROCESS
http://i.imgur.com/9TrDj1H.jpg
http://i.imgur.com/r10qLhL.png
http://i.imgur.com/SLtIvIc.jpg
http://i.imgur.com/teyviy3.jpg

AFTER
http://i.imgur.com/0Og04Lm.jpg
http://i.imgur.com/JFwnOVw.jpg
http://i.imgur.com/g6RLooY.jpg
http://i.imgur.com/NAABYV2.jpg

Thank you for all your help.
This thread can be closed

 

[oldcatamount]

Re: Oh no! Ive done a bad thing need machining advice.

Good job Buddy! "If there's a will, there's a way"! You saved a ton of $$ and you must be quite satisfied with the experiance!