honda gx390 rusty cylinder

[Az Shadeguy]

I have a gx390 that looks like it had water in the cylinder at some time.
The rings are stuck in the piston.
The rust is not very thick Would a ball hone take care of this without having to go with oversized rings?
The cylinder measures 3-9/16 would a 3-1/2 hone work what grit should it be?

[KE4AVB]

With rust it can be pitted in places.

Cylinder specs for a standard bore on the GX390 are 88 mm x 64 mm [3.5" x 2.5"]. On my caliper 3.5" converts to nearly 88.89 mm. Double check your measurements. If it is already 3-9/16 [90.4mm] your in the oversizing range already as I would ovaling and tapering has occurred.

You use a 280-320 grit should fine for just rust and glaze breaking. Note a ball or flex hone will clean up and make any cylinder oval or taper worse. Here I use 180 grit for finish resizing cast iron sleeves and only 280 grit for aluminum bores.

EDIT: Also if the cylinder is at 3-9/16 you're already pass the available oversizing parts of .75 mm [.030"].

[creia]

How (what measuring tool) did you measure it?
Michael

[Az Shadeguy]

I measured it with a tape measure just to see what size of ball hone.
Now I have used a 3" ball hone and cleaned it up about 90%.
When I used a bore guage and a digital caliper{both harbor freight] I get range of 87.93 to 87.98 measuring top, middle and bottom both horizontal and vertical.
This engine looks to have very few hours on it.

[creia]

OK, now we're talking! Your measurements of 87.93mm to 87.98mm are a hell of a lot better than the 3 9/16" (90.5 mm) you originally provided.I suspected that you used a tape measure and that is why I asked.
Michael

[KE4AVB]

When I used a bore guage and a digital caliper{both harbor freight]

I have tried those telescopic gauges from HFT but found they weren't as accurate as a set of manual gauges I have when used with the digital caliper. Maybe just me but the reading were consistently short of my manual caliper; of course, my manual caliper has sharper points when compared to those rounded ends of the telescopic gauges.

But anything is better than a plain old tape measure when we talking about fractional amounts in the thousandths.

[Az Shadeguy]

I have tried those telescopic gauges from HFT but found they weren't as accurate as a set of manual gauges

What kind of manual gauges? Do you have a brand name?

[KE4AVB]

I usually the circle item for inside cylinder measurements along with my digital caliper. The others I seldom use except in my wood working projects; unless, what I need measuring is not easily accessible.

[Dale_W]

KE4AVB
Thank you for posting that picture. I know buried somewhere in a drawer I have a caliper like the one circled.

I recently acquired a Honda HR215K1 HMA mower. (beautiful machine, when the engine ran). You may recall my recent posts asking about a replacement engine for that mower.

Roym was correct in his assessment that I am not comfortable rebuilding an engine for somebody else.

At some point in time I will open the engine up, and depending on what all is wrecked, I may take some measurements and see about an oversized piston and rings for it.
I am comfortable rebuilding an engine for me.

My son has a Yamaha ATV, single cylinder 660 cc four stroke overhead cam. The stealership was happy to sell me a once-over piston and rings. (for this, once over means .20) and they sent out the cylinder (with new piston) to be bored. Wow. Who ever bored it did a great job matching the bore to the piston.

If the Honda engine is not too far gone, I may have it bored, by somebody. There is a Harley Davidson Shop about a mile from my house that does all engine work.

Do you think they'd give me a good price on a Honda engine bore job? hahahah

OK not gonna hijack this thread.

Just wanted to say thanks for the picture.

Dale

[Az Shadeguy]

I usually the circle item for inside cylinder measurements along with my digital caliper. The others I seldom use except in my wood working projects; unless, what I need measuring is not easily accessible

Thank you I will try one of those
Do you keep the piston in while checking bore?