engine rebuild - rust in cylinder

[antus]

I am currently trying to rebuild and boost an isuzu g200w motor. Ive had it for 10 years in my shed (maybe more) - supposedly rebuilt. That appears to have been true, but when we tried to turn it we found it was seized. I got some mates around and we pulled it apart trying to get it moving but in the end we found some water had gotten inside, and the rings were rusted to the bores. 2 cylinders were OK, but another 2 were not. We lubricated it and knocked the pistons out. I can feel that the cylinder wall on the bad 2 is not smooth, but I have no idea how serious to take the condition of these bores. My mates are telling me to get a flex hone to clean it up and then put it back together. I am not so sure. The rings look OK (not pictured), and I have another set of standard size rings so can replace like for like easily enough. A lot of the roughness I can feel does appear to be rust on the surface but there has to be something missing from the cylinder wall because the rust has come from nowhere.

Would a hone with a flex-hone be enough?
How bad does it have to be before thinking about machining and re-sleaving?
If I do some machining to clean this up, would I be able to run standard size rings still or would I need to get oversize?

Mates are saying they've seen on youtube that you need to take some metal off the ends of the rings to stop them expanding too much, but Ive not heard of this and see people running 12-14 psi on stock engines with stock rings. First plan is about 8psi then up to about 14 at a later phase. Is this something I need to worry about? Or if I hone the bores a bit will it all just even out in the wash for this application?

[brindo]

What would the bores look like if you cleaned them up with scotch brite? Would they be deeply pitted?

[immortality]

A light hone may be ok if there is no pitting.

As for the ring end gap, you're mates are correct, it really depends on how tight the rings are. Check the manufacturers recommended ring end gaps for the application and compare ring gap between a n/a and boosted enigne, opening them up a few thou more won't hurt performance but will give you that little extra margin for that day things get a bit to hot. Honing the block a few thou may also slightly increase the ring end gaps.

[VK_3800]

My answer for both questions would be you have to try it and see.

The hone may do the trick but you won't know until you've done it whether its good enough or not.

Same goes for the ring gaps - measure them as you normally would (once you have a good bore) and if the gap is smaller than ideal then file them down.

[vlad01]

Personally I would rebore and torque plate hone + forged pistons. Its not expensive especially that its a halfer.

[oldn64]

Hello Antus,

Yes your mates are correct. The ring gap is there to stop ring bind. This is caused when the ring expand with heat and the gap zeros and then the ring pushes against each other distorting the ring and either breaking the ring or piston or both.

The gap is one of those things that needs to be controlled though, while yes a ring gap will not help performance directly it does have some reflection on it. A too wider gap will not hold cylinder pressure fully and thus cause the cylinder pressure to bleed off causing blow by, on the opposite side as explained above too little will produce nasty results.

So yes it is better to have a slightly wider gap than too little. The big thing here is that you are looking to force induction this motor so from a heat perspective a wider gap will be needed as a safety margin. Yes you might have found that standard has be done before, but how many have been pulled down and looked at afterwards.

Anyone can assemble a motor, it takes attention to detail to build a motor. I was taught long ago when I was running around calder as a young racer, racing is about heat management, if you components are under stress now ad some heat and teh result can be disastrous. Net result, give the gap a tickle.

the rust does not look too bad, but 2 thou of pitting can cause issues, which your fingernail will pic up. I would wash and clean the block to start with. run your finger down the bored and feel with you finger tip, if picks up then it will be 2 thou or more. a hone with either a dunny brush or hand drill spring loaded unit will generally clean up 5 thou of your bore size. A hone will be 10 thou or more. As you plan to stress this motor I would not cheap out and get it hone plate bored. Thsi will result in a better build with longevity as the outcome. Save $100 now may result in a complete rebuild again in the future, not my idea of fun.

Cheers
oldn64

Took 3 years to build the titanic, and only 2 hour 40 minutes to sink it.

[Holden202T]

this might help

[antus]

I ended up taking thos engine to an engine shop for a hone, and a clean. Also got the flywheel machined because it wasnt great. Then other stuff got in the way but i'll be getting back to it soon. I think from what ive been told the bores cleaned up ok (passes the nail test). Tried to fit g200z rings but they were too fat. Also need full custom pistons as they're domed unlike the single cam ones which are off the shelf. So now its all cleaned up we'll get it back together and see how we go. Maybe not more than about 8 psi boost, though (was going to update the existing turbo, but this might not be the engine for that. We'll see.)

[oldn64]

Hey antus,

mate of mine put the 2.6 out of the rodeo into his gemini back in the day Apparently the changed where the engine number was to it was cloaked as a g180......

are your domed pistons high dome or recessed? What was the original pistons for these motors? what are you hoping to decompress too?

I forgot to add to my post that a hone will generally mean a increase of piston size. 5 thou you can get away with but if stressing the motor then go the 10thou and up a size.

At least you are heading in the right direction. If you wish me to see what piston i can find for you let me know. I have used some weird combos before to get what I wanted (read toyota pistons into a Holden 202 to accommodate the stroker I made. [crank designed by myself and built by a crankshaft engineering firm] was a monster)

keep up the workings, i have a soft spot for these motors.

cheers
oldn64

[antus]

We got the pistons back in last night. This is the first time we've done this but so far, so good.

The piston here is one of the spares, it didnt end up in the engine.