What is the proper way to check cylinder bore roundness?

1988 V6 Evinrude 225

When checking the cylinder bores for roundness, should the crankcase casting be bolted to the block and torqued to spec. or doesn't it matter?

I will be taking the block to a local engine builder who has all the proper equipment to check the cylinder bores and pistons.
I just don't know if I should bring it to him with the crank casting installed and all the bolts torqued. At minimum I plan to install the crank casting loosely bolted to protect the mating surfaces.

Thanks in advance for your replies.

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

He just needs the block, no need for front half or crank when machining or measuring.

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

Thank you.

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

is that the right term?? CONCENTRICITY?

concentric to what???




where the rod mounts on the crank??


I am thinking about this and i cant see where the bore is concentric to anything...

do you mean ROUNDNESS, or Taper??

concentricity is two round features on the same center...or withint a certain spec of being on the same centerline.

likea prop shatf has a bearing dia on one end and a bearing dia on the other, with a larger hunk of metal feature in between.

it is important that the bearing dia's be concentric.

not being a bafoon...just trying to grasp the question

bob

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

Guess I should have looked that one up in the dictionary before I used it. LOL No offense taken.
I'll go back and edit that if I can.

More correctly stated, when checking the bore for roundness should the crank casting be bolted on and torqued to spec. I don't see how taper would be affected with or without the crank casting installed. I was wondering if stress exerted on the block by the bolts pulling the mating surfaces together could affect the roundness readings. Faztbullet has already given his opinion. What's yours?

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

The 1988 is a open deck block and it will be worn in a taper, you measure cylinder at bottom ,middle around ports and top..



Make sure since you have it down to vent the lower bearing as it makes the recirculation system work like it should and engine idle's so much better

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

Thanks for the diagram showing the locations to check the taper. I will bring it with me when I bring the block to be checked. The shop does not work on outboards, but they are close by and offered to check the pistons and bores. If I give them the specs and the proper locations to measure the taper, they can handle the rest. Once I know what needs fixing, I need to find a good machine shop that works on outboards here in CT.
I had read about venting the casting a long while ago, and had forgotten all about it. How critical is the placement of the hole. Looking at the last picture I would say I can probably get it within 1/8" of the one shown. Does the old one just get blocked off or could you put a tee in and use both of them?
Thanks for the tips!

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

No the new one is a vent and the other is recirc to upper bearing.line

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

Faztbullet said:

No the new one is a vent and the other is recirc to upper bearing.line

Click to expand...

a vent?? where is it vented to??? it seems like it has to be plumbed to someplace....since it is new...how is it incorporated into the hoses that are stock and where does it go??? I stilllllllllll, havent put my motor back together and Id love to hear all the tips i can before i start( this winter)

bob

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

Faztbullet said:

The 1988 is a open deck block and it will be worn in a taper, you measure cylinder at bottom ,middle around ports and top..


View attachment 169946
Make sure since you have it down to vent the lower bearing as it makes the recirculation system work like it should and engine idle's so much better

View attachment 169949View attachment 169951View attachment 169952View attachment 169953

Click to expand...

I seam to remeber being here, asking the same questions. I like my pics..... lol

Just to shime in, this litle fix/retro fit makes a huge difference!

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

for some reason i thought this was an ocean pro motor......maybe this trick isnt needed on my motor!

bob

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

OK. I had envisioned that the new hole was a better location and the hose moved to the new location.
So you are saying all the recirc lines go back as they were and the new hole is just vented to atmosphere. Don't gas vapors get pushed out of the new hole?

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

So you are saying all the recirc lines go back as they were and the new hole is just vented to atmosphere.

Click to expand...

That is correct....

Don't gas vapors get pushed out of the new hole?

Click to expand...

Its a vent as very little vapor escapes, the hose you attach will follow the recirc line to top of block...

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

Faztbullet:
So this vent is allowing the recirc valves to pull the fuel and oil that collects in the lower bearing back into the intake manifold to be burnt. I take it the recirc system as designed did not have sufficient vacuum to pull the oil up and into the intake, and the vent fixes that. Just trying to understand why this works rather than blindly doing it.
J.K.:
I searched and found your engine rebuild thread. That will be very useful and will probably save you and Fazt a lot of typing.

Faztbullet:
I have another thread asking about decking the block to clean up corrosion around the tops of the cylinder walls but only had one reply. As mentioned in that thread, the corrosion has not reached the liner but it is getting close in a few spots. My thought was that decking the block would clean some of that up, giving the head gasket more contact area, and buy some time. I don't want to spend a lot of money getting it welded and machined as this power head will just be a spare in case one of my engines on the boat fails. I will probably be getting a different boat in the next two or three years. What are your thoughts on the benefits or pitfalls of decking the block. I know that decking can raise compression beyond safe levels but thicker head gaskets can be used to compensate.

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

You can deck the block .020 and be safe and they do not make a thicker(low compression) headgasket for this motor that I know of. If its material missing you can clean and build up /replace it with aluminum Devcon epoxy then just have the deck trued which is what I myself would do.

So this vent is allowing the recirc valves to pull the fuel and oil that collects in the lower bearing back into the intake manifold to be burnt. I take it the recirc system as designed did not have sufficient vacuum to pull the oil up and into the intake, and the vent fixes that. Just trying to understand why this works

Click to expand...

This is just a open vent line that vents the lower bearing, at idle and low speed excessive fuel that recirculating system did not purge for # 5 and 6 cylinder loads up in bottom bearing area and on sudden accelerator can cause a bog as raw fuel is thrown in cylinders and fouls plugs momentary or causes these cylinders to load up at idle. All the late model newer blocks have this modification from the factory.

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

This does make a huge difference. If in you are unsure, just think of it as it is easily removed by putting a vacuum plug/cap on it. You will not do this off coarse. I idled mine a bit (2-3 minutes) and shut it down. Then took off the hose. You would be suprised at how much fuel comes out of that hole. It works. It allows air into the bearing and helps the motor suck fuel out of the bearing.

Re: What is the proper way to check cylinder bore concentricity?

Re: What is the proper way to check cylinder bore concentricity?

I'm definitely going to do the mod.
I need to put this project on hold for a few weeks while I get the boat put away for the winter.
I did remove the crank and pistons from the block today. Pistons are not scuffed up and the bores look like they will clean up with a ball hone. Provided the checks on the pistons and bores are in spec. I should be in good shape.