The manual says this is un-repairable

[Brian]

This is that 75 hp Chrysler I've been working on. The bottom cylinder had a piston ring break and scored up the cylinder. The patch of shiny stuff in the middle is aluminum debris that used to be piston and is now impacted crud.

Anybody got an idea how much can be bored out safely? I thought I saw some rings made for 0.003" overbore. If nothing else, I have the other motor and as long as the cylinders aren't scored, I can use that.

[Tim_Mattson]

Chrysler

Brian ,
I`m pretty sure you are right on the .030 ,any bigger and you get to pay for a sleeve install.
These have really high compression(up to 175 psi) so I`d say use the other block instead of hoping it doesn`t re-occur next to the repaired cyl.
I`ve seen spark plugs blown out of Cyl. heads with there steel inset sleeve still screwed onto it (not sure why they always use these on Force /Chrysler,maybe for heat expansion....).
This sometimes was in the very hole with all new stuff.
I`d use that spare block and proceed with more money in your pocket when done......

Those motors do have huge shafts and gears in their lower units with some parts very expensive and in limited supply.Make sure you have a good lower and hopefully a spare before hopping up the block.
Others may have better or different advice so keep watching.
Tim M

[ChuckB]

Don't throw a lot of money at a Chrysler. Good motor while they run, but very difficult and very expensive to get parts for. The manual is correct, but for the reason of expense, not impossible.
ChuckB

[Twinblade]

Hard to tell the extent of damage from pics but if you have the time, it might be possible to salvage the block. We used to use this trick with the Yamato and Koenig alcohol engines we used to race. These engines are very tempermental and will stick with alarming regularity. Get some muratic acid (concrete etchant) from your local hardware store. Take some Q-tip swabs and rub the acid on the transfered aluminum. Keep doing this until all the aluminum is removed. Judging from the pics, it looks like you have a lot to remove so be patient. Once all of the aluminum is removed you can run a good quality rigid hone (Sunnen or Amco) down the cylinder. I don't see any huge scores in the block and once all of the aluminum is removed, the results might surprise you. If there are light scores below the ports, it probably won't hurt you. Good luck, hope this helps!

[Brian]

So I finally got it down to the machine shop. He bored that one cylinder out and told me to get 20 thousandth's over pistons. So now those are on order. He'll hone the block to match the pistons.

I'm kinda stuck with these two (70 & 75 hp) Chryslers. The 70 came with the boat and I'm already into it $200 for the tilt trim motor, plus I already have the carbs and fuel pump rebuilt. Hopefully it will all be worth it when I'm done and have a parts motor in reserve.

Ideally, I'd like to have twin 40 Evinrudes on the back of this boat. The extra wide splashwell and being built here next to the Columbia tells me it was made for twins. Just my guessing though.

Thanks for the inputs

[Bflaherty]

So I finally got it down to the machine shop. He bored that one cylinder out and told me to get 20 thousandth's over pistons. So now those are on order. He'll hone the block to match the pistons.

As a bit of advice from when I rebuilt my Merc 1000, get a price quote on machining all the cylinders to 0.020 over. We only did the bad one and now the motor has an odd sound as one cylinder is producing more than the others and the compression ratio changed in the one hole which makes it sound a little off at low speeds. In hinesight I would have bored all 6 cylinders instead of just the one...

~Brian

[Brian]

the block is back

Big day arrived, the block is home from the shop. Yeah, I was king of suprised when the machinist asked if I wanted to do all the cylinders or just the one. I did em' all without hesitation. It just didn't sound balanced with one over size piston. The 70 hp I disassembled for the parts had a 0.010 over and two standard. The rebuilt block has three 0.020 pistons honed and bored cylinders to match. Should have great cmpression.

The welded collar on the crank had to be sawed off (by hand) to salvage the lower bearing. It was in fine shape after the collar was out of the way. (that was about a solid hour of sawing)

Only three more snapped off bolts to extract. Getting pretty good at that by now. The main thing is being patient and using all the tricks. Just a day or two away from starting the re-assembly. I want to be on that river this summer.

[slo-mo]

cutting losses?

I'm not sure if you are insane or incredibly patient, Brian. Most old outboards I have worked on were fried after years of hapless owners forgetting that 2-strokes require oil, water pumps and basic mechanical common sense.

After reading of your hacksaw adventure and snapped bolts, I'm going out to the shop-put my head in a vise, and smash my thumb with a ball peen to remind myself of all of the wasted hours that I've spent being too cheap to buy anything new.

Then I'm going to get to work on...

I hope that your investment gives you many happy memories.

[Brian]

Insane? Certainly not. Stupid? Well,... yeah, maybe.

If necessity is the mother of invention, then being broke is the mother of patience. And of course the ultimate mother is a broke outboard to bring it all together.

With two motors, I should have one good one when I'm done. The other thing is I'm getting to know this engine inside and out and I have a lot more faith in it if I rebuild it myself.

Old boat + broke engine = Mission

[Brian]

the rebuild continues,...

So the block came back from the machine shop with a lovely crosshatching in the cylinders and a freshly machined parting surface for the cylinder head to mount on. The exhaust port still had some snapped off bolts in it. Once I repaired those, it was time to 'machine' that surface.

Pulled out my strait edge and checked all my planes. The old jointer plane was true so I used it, very carefully, with 120 and 400 grit paper, using Liquid Wrench penetrating oil for cutting fluid. Results were pretty good.

Used the table saw for a machined flat surface to lap the exhaust plate. The one from the 70 hp motor was in better shape, but lacks 4 cut outs for water flow, so I drilled a small pilot hole and gouged out and shaped the cut-outs with an old 1/4" bench chisel.

End result was a very tight mating surface between the plate and the exhaust port. Largest gap was ~0.004". This weekend I'll power wash the block and start assembly. This better work!

[Brian]

looks good, it better run

Finally got to the part where it starts looking like an engine. Still have some cleaning and finishing to do on some parts as they go back on. The primer on the fly wheel is drying now. The elecrtical harness is partly mounted. This thing better work.