OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines B&S 19.5HP scoring after rebuild

Hi all,

I'm looking for a second opinion on some issues I've got after rebuilding a 19.5HP single cylinder Intek engine, model-type-code 31P677-0138-0907....etc.

The cylinder was honed and new rings put in, and the top main bearing sleeve/insert under the flywheel was replaced. Around 10 hours of operation after the rebuild, the cylinder walls are scored at 9 and 3 o'clock looking into the bore from the head side (image 1, 2). The scores aren't deep - I can barely feel them, and a 0.002" feeler gauge feels massive in comparison - but they still shouldn't be there I think. This engine is on a Greenfield ride on and it did at least an hour of real hard work cutting tall grass at around 2-3 hours after the rebuild.

The scores/scratches are clearly a result of wear between the piston skirt and the bore - they stop before the rings do at the top of the bore.

So far I've put it down to not cleaning the engine well enough after honing before reassembly. All the advice I read (now) is that the bore should be thoroughly washed in hot soapy water and then wiped down with oil or similar - my cleaning procedure wasn't so good in hindsight. All I did was wash the bore with cold water and detergent, and didn't pay much attention to the rest of the engine block beyond making sure there was no visible honing grit in it. Then, of course, I did a poor job of drying the bore and forgot to oil it, causing it to rust slightly. This light rust came off easily with a bit of fuel on a paper towel, but I didn't do any more cleaning beyond that. It looked clean, but now I suspect it wasn't.

I changed the oil at the 6 hour mark and what came out looked pretty nasty (image 3) with lots of small specs and filings that are attracted to a magnet. The engine has an oil filter but is not pressure lubricated (the oil pump just circulates oil through the filter).

My question is, do you think this sloppy cleaning procedure can be blamed for the scoring and metal in the oil after running the engine for a few hours? At this stage I can't see anything else that would've caused it.

Thanks in advance,
RLP

Hi RLP

Quite probably the heavy slashing with that metallic soup in the sump caused at least some of the damage. Normally I run in mowers for 10 minutes at idle, then 6 hours of light use.

May I ask what made you take the head off again? Is it now burning oil or down on power?

Also, what is the burn like - i.e. what does the plug electrode look like?

Hi Tyler and thanks for the quick reply,

I have attached an image of the spark plug - doesn't look too bad to me, but I'm no expert on reading them.

I had just pulled out the plug to check its appearance, and while I was doing that, shined a light through the plug hole to have a look and saw scoring, which prompted me to take the head off. There weren't any other obvious symptoms.

I did run it at a varying idle speed for 15 min or so on first startup, and then did a couple of hours of light work before the heavy mowing. But I probably should've known better and changed the oil before doing heavy work with it.

RLP

Plug doesn't look too bad RLP (slightly lean, but no burnt oil), I bet seeing the scoring was one of the 'oh s***' moments

As long as its not burning oil, making more noise or down on power, you could probably leave it.

Out of interest, what weight oil did you run in it?

Any engine with scoring (although this case minor) won't last as long as one without, so maybe try one of the engine oil additives with PTFE in it to prevent a bit of further wear. Now I am no great fan of these snake oils, but after the excellent job the oil stop leak did on 2 lower main bearings, there are some I believe in.

That being said, I would never suggest any that effect the viscosity (stop leaks and PTFE don't change viscosity).

Nulon Worn engine repair with PTFE is supposed to help restore engine compression. I have no vested interest with Nulon, just use their products.

Nulon was one of the first in the late 70's to get the PTFE to remain in suspension and has been on the market since in one form or another. They ran a 161 Torana (from memory) melb to sydney without oil (just the prior PTFE treatment) and there were no substantial damage on tear down beside a bit of play in a couple shell bearings (can't remember which). Think they installed solid lifters at hydro ones couldn't possibly work without oil.

That being said, I don't think any more scoring will occur after your oil change. Maybe run another 2 hours with current oil then drain to see if any more filings.

Regards
Tyler

Yeah, I was pretty disappointed upon seeing the scoring, so soon after having worked on the engine!

I was running regular 30 weight oil in it at the time, mono grade because that is often advised for engine break in. Usually I use either that or a Penrite 10W-30 semi-synthetic oil designed for small engines which is available at a good price locally.

I agree I could probably leave it, it still seems to run fine. I will keep those PTFE based additives such as the Nulon one you mentioned in mind, I might try that if it starts burning more oil or losing power. Definitely worth a try before tearing into an otherwise OK engine.

I recently came into possession of an old running 18HP B&S Vanguard V-Twin engine which will be used on the Greenfield this engine was on, so this engine may actually end up going on another machine where it sees less demanding use, and the scoring would be less of a concern there I think.

RLP

I just noticed something else which may explain the increased wear.

I recently got another engine block back from a machine shop who bored and honed it, and I just noticed that my honing marks on this scored engine are much deeper and scratchier than those done by the machine shop on the other engine block - so this may have lead to increased wear and metal particles in the oil which caused the scoring.

The lesson? Don't use a cheap hone, and use plenty of oil on it I guess!

RLP

When to your honing tool are using a ridged hone? You also should using 280 or 320 grit stones. And yes plenty of honing oil and cleaning several times during the process as the oil and aluminum dust will build up throwing off your measurements.

Ridged hone removes both taper and ovaling of the cylinder where a flex just magnify these.

No, it was a flex hone with 220 grit stones. I was just trying to deglaze it, no major resizing needed, but quite possibly the wrong tool for the job. Thanks for mentioning that AVB.

RLP