Cylinder honing opinions

[sgkent]

I did it for a living in a machine shop many years ago, learning that trade from a master who built engines and racing cars for the Unser family and others. Also street cars, classic cars, fleet cars, motorcyles etc.. Generally the bore is sized to the individual piston. It is not cost effective for a small engine when engines from China that are Honda clones aren't all that expensive. But there are shops that do it if you want it done. Call me an idiot but I would rather restore an engine to like new than buy a new one. Not always. I cannot get what I want new normally unless I do it blindly, and so many times what you get is not what was advertised. That said, time is worth a minimum of $100 an hour in any trade these days, plus materials, and it is about a one hour process to get it right. Whether it is bored then honed, or just honed, the final process is a rough stone is used then a finishing stone the last little bit. Moly rings take a special finish. For a lawn mower, if the cylinder has normal wear, a bottle brush finish is 2 minutes unless you know someone with a Sunnen hone who owes you a favor. That said, if you need to bore it oversize, the valve guides, and maybe valve seats are gone too so better know someone who does them. Typically a go-cart racer will know people who do these things.

James Condon built an engine recently that the bore was too corroded to use so a subscriber named Ron on his channel with a Sunnen hone offered to bore it .020" over for him. He showed a few seconds of the process on the sunnen hone, but I just looked thru that video a dozen times and can't find the segment so maybe he edited it out. I looked up auctions in case anyone wants to DIY, and a recent sale of a CK10 sunnen hone was $7800. That is 50 year old (and 3-phase) technology but precise. You can buy a lot of lawnmower engines for $8000. In Condon's situation, the engine was a almost zero hour engine that someone had not used so moisture had destroyed the cylinder. We saw a video today of an almost zero hour Cessna 182T that had been sitting in a hanger for 14 years in Idaho, but the moisture in the air had just destroyed the inside of the cylinders. Cost them a small fortune to have it rebuilt.

 

[Tiger Small Engine]

I did it for a living in a machine shop many years ago, learning that trade from a master who built engines and racing cars for the Unser family and others. Also street cars, classic cars, fleet cars, motorcyles etc.. Generally the bore is sized to the individual piston. It is not cost effective for a small engine when engines from China that are Honda clones aren't all that expensive. But there are shops that do it if you want it done. Call me an idiot but I would rather restore an engine to like new than buy a new one. Not always. I cannot get what I want new normally unless I do it blindly, and so many times what you get is not what was advertised. That said, time is worth a minimum of $100 an hour in any trade these days, plus materials, and it is about a one hour process to get it right. Whether it is bored then honed, or just honed, the final process is a rough stone is used then a finishing stone the last little bit. Moly rings take a special finish. For a lawn mower, if the cylinder has normal wear, a bottle brush finish is 2 minutes unless you know someone with a Sunnen hone who owes you a favor. That said, if you need to bore it oversize, the valve guides, and maybe valve seats are gone too so better know someone who does them. Typically a go-cart racer will know people who do these things.

James Condon built an engine recently that the bore was too corroded to use so a subscriber named Ron on his channel with a Sunnen hone offered to bore it .020" over for him. He showed a few seconds of the process on the sunnen hone, but I just looked thru that video a dozen times and can't find the segment so maybe he edited it out. I looked up auctions in case anyone wants to DIY, and a recent sale of a CK10 sunnen hone was $7800. That is 50 year old (and 3-phase) technology but precise. You can buy a lot of lawnmower engines for $8000. In Condon's situation, the engine was an almost zero hour engine that someone had not used so moisture had destroyed the cylinder. We saw a video today of an almost zero hour Cessna 182T that had been sitting in a hanger for 14 years in Idaho, but the moisture in the air had just destroyed the inside of the cylinders. Cost them a small fortune to have it rebuilt.

Occasionally I will get a call about honing a small engine or where a machine shop is that does this type of work. We are in the remove and replace business now, and have been for many years. It is too labor intensive to rebuild parts these days.

 

[slowleak]

I worked in a small engine shop in the 80's for a few years, we were an autoparts store that had a machine shop and a Kohler/Briggs/Honda dealer at the time.
We had various pieces of equipment to handle small engines, it all depended on the size and material being bored. On the larger iron engines, they were treated more like an automotive engine, they got mounted up on a fixture and we would size the bore to fit the piston that was to be installed.
It was a cutting operation first, then the cylinder was honed to give the surface finish required for the rings to seat.

What was most important for good results was to have the piston in hand that the customer wanted to use. Pistons can vary several thousandths of an inch over a given size and that had to be taken into account when the engine was machined.

We did a lot of Kohler engines, probably a dozen or so a week, mostly the K series singles, K181, K241, K301, K321, K341, etc. We also saw a good many aluminum cylinder 2.0 to 4.0 hp Briggs Stratton mower engines. Most got bored to .020 oversize, rarely did we have to set up to do one any larger. They were done the same way, but we had a bench top fixture for the small engines, they were done with a boring bar sourced through I believe Foley Belsaw years ago. It was a fairly quick process followed up by a fine honing and wash. The charge then was only $10 or $15 per hole. We did a lot of motors for other shops too, so they'd send us a dozen or more at a time to do all at once, which made it easy since the set up was mostly all the same for each one.

 

[Tiger Small Engine]

I worked in a small engine shop in the 80's for a few years, we were an autoparts store that had a machine shop and a Kohler/Briggs/Honda dealer at the time.
We had various pieces of equipment to handle small engines, it all depended on the size and material being bored. On the larger iron engines, they were treated more like an automotive engine, they got mounted up on a fixture and we would size the bore to fit the piston that was to be installed.
It was a cutting operation first, then the cylinder was honed to give the surface finish required for the rings to seat.

What was most important for good results was to have the piston in hand that the customer wanted to use. Pistons can vary several thousandths of an inch over a given size and that had to be taken into account when the engine was machined.

We did a lot of Kohler engines, probably a dozen or so a week, mostly the K series singles, K181, K241, K301, K321, K341, etc. We also saw a good many aluminum cylinder 2.0 to 4.0 hp Briggs Stratton mower engines. Most got bored to .020 oversize, rarely did we have to set up to do one any larger. They were done the same way, but we had a bench top fixture for the small engines, they were done with a boring bar sourced through I believe Foley Belsaw years ago. It was a fairly quick process followed up by a fine honing and wash. The charge then was only $10 or $15 per hole. We did a lot of motors for other shops too, so they'd send us a dozen or more at a time to do all at once, which made it easy since the set up was mostly all the same for each one.

$10 bucks to bore and hone a cylinder is incredibly cheap by today standards. Imagine doing this to a push mower in 2026, while adding new rings, and labor to remove engine, open the case, clean valves and head, new gaskets and seals, and replace engine. That’s why it isn’t affordable at $125/hour labor.