regular piston in cool bore engine

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chazdaddy

New Member
#1
#1
Like a few others, I am addicted to looking in CL for old Briggs 5hp FH's for cheap. Over time, I have acquired more than I need but keep looking anyway. They usually don't run and can be challenging to fix, but hey it's fun for me.

It's interesting to see the different things that go wrong with these engine. It's amazing how tough they are, there are some good engines out there that just need the carb cleaned, but some do have internal damage/ failure.

The last one I got has a fair amount of galling all the way around the piston and bore. Engine shows signs of some new parts, looks like has new piston and hone in the bore. Didn't run very long because had another problem that stopped it. Thinking about what to do, I realized probably was rebuilt with non-chrome piston in alum bore.

Galling is slight, so pics probably would not show it, so no pics. Anyone else every see this, or maybe another issue caused the galling. :shrug:
 
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chazdaddy

New Member
#5
#5
I thought maybe I misspelled the word, so found the following definition:

"Galling is adhesive wear. Galling is caused by macroscopic transfer of material between metallic surfaces, during transverse motion (sliding). Galling occurs frequently whenever metal surfaces are in contact, sliding against each other, especially with poor lubrication. Galling often occurs in high load, low speed applications, but also occurs in high-speed applications with very little load. Galling is a common problem in sheet metal forming, bearings and pistons in engines, hydraulic cylinders, air motors, and many other industrial operations. Galling is distinctive from gouging or scratching in that galling involves the visible transfer of material as it is adhesively pulled (mechanically spalled) from one surface, leaving it stuck to the other in the form of a raised lump. Unlike other forms of wear, galling is usually not a gradual process, but occurs quickly and spreads rapidly as the raised lumps induce more galling."

So, appears the damage I am seeing probably happened with very little run time.
 
creia

creia

#7
#7
Typically, top end wear (especially "scoring" or "galling") is from dirty air with dust particles due to running an engine with a dirty filter, (or worse) NO filter in dusty conditions.
You mentions that the engine had a new piston and hone. I am assuming that to tell it has a new hone, you can see the classic "cross hatch" pattern on the cylinder walls? If that is the case and there is scoring/galling visible that indicates it was a fairly recent condition, especially if it was "slight" as you indicated. If scoring/galling had been happening for a long time that cylinder wall cross hatch pattern would be worn off.
Finally, indeed if that Kool-Bore has a non-chrome piston, (which is a BIG "No-No"!) as you seem to suspect, I believe that could account for the condition you see as well.
Michael
 
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chazdaddy

New Member
#8
#8
Thinking about it, engine probably was run without adequate air filter. Engine came with a poor fitting make do air filter. Engine was on yard kart, so probably did eat some dirt. So if dirt caused the galling, maybe has right piston after all?

I am just trying to decide if should start over with another piston (a known chromed piston) or hone cylinder a touch and go with what I have. Actually, not a lot of downside to go with what I have. If it works OK, great. If it continues to gall, then I will know it's the piston.

Thanks for replies. :thumbsup:
 
creia

creia

#9
#9
If you are going to open the engine up (actually it sounds like you already have?) NOW is the time to really check it out thoroughly. I definitely would NOT recommend a honing (yet) until you have checked out that cylinder in further detail. If that cylinder wall is already worn oversize (enlarged in diameter) beyond Briggs "reject" specs, you will actually WORSEN the performance by honing which enlarges it even more. You need to take some accurate measurements of the cylinder wall- top, mid-way and bottom and check for oversize, out-of -round, and taper conditions. You need an accurate t-bore gauge and micrometer to do this - not very expensive at all from HF. Briggs publishes "reject tolerances" for all of these conditions. If you are over "reject" tolerances on any of these, you must BORE and HONE the cylinder wall oversize AND purchase a matching OVERSIZE piston and ring set- This gets expensive, and is generally not cost effective on an aluminum "Kool-bore" engine, unless you are sentimentally tied to this engine for some reason. While you are at it check to see if that is the correct (chrome) piston and how worn the rings are by checking "ring gap" as well.
Good luck and report back with your findings.
Michael
 
creia

creia

#11
#11
Stangrcr1 said:
Is it possible it was overbored and was not honed large enough for piston expansion?
Click to expand...
Stangrcr1 makes a very valid point only if indeed there IS an "oversize" piston/ring set installed. You can tell by looking on the top of the piston where it will have 010, 020,030, etc. embossed. (No numbers embossed= stock size piston.) If it does, the piston to wall clearance is CRITICAL and the machinist must very carefully match the cylinder wall overboring/honing to the piston size.
Michael
 
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chazdaddy

New Member
#12
#12
Engine is completely disassembled and soaking in diesel oil to clean off old burned on gunk.

creia's comments are excellent and remind me of my Casita travel trailer. There is a very cool Casita forum, has tons of good info and lots of nice helpful people like this site. Often something goes wrong and needs tweaking to get to work, (furnance, refrigerator, hot water heater, blower fan, propane regulator, etc). That site has saved me a lot of repair $'s over the years.

Once I had a problem with the microwave and made a post for trouble shooting ideas. I got several comments about voltmeters, checking voltage, checking my power converter, technical stuff I don't understand, equipment I don't have. I didn't do any of that, I just pulled the microwave out (had to take facade off that was pop-riveted on) and it was partially unplugged. I plugged it in and problem solved. I felt like a genius. :thumbsup:

I agree with creia, engine not worth spending $'s on. I plan to clean it up, put it together, run it, maybe take it apart and have a look inside. If it runs good OK. If it smokes bad or bore gets worse, I will use it for spare parts.

Thanks for comments. :smile:
 
old-timer

old-timer

Scamming Member
#13
#13
Well I wouldn't necessarily say it's not worth spending money on :shrug:
IMHO they don't make flat heads anymore, and there are a number of things you can do to to rebuild it, should you choose to. Depending on if it's stock bore, you could send out the block and have it bored 10 or 20 over. Then all you need to do is pick up a new piston and ring set . Just something to think about :shrug:

Vic
 
Stangrcr1

Stangrcr1

New Member
#14
#14
creia said:
Stangrcr1 makes a very valid point only if indeed there IS an "oversize" piston/ring set installed. You can tell by looking on the top of the piston where it will have 010, 020,030, etc. embossed. (No numbers embossed= stock size piston.) If it does, the piston to wall clearance is CRITICAL and the machinist must very carefully match the cylinder wall overboring/honing to the piston size.
Michael
Click to expand...
Same applies for too much clearance as the piston will slap the side of the bore...
 
Boomstick

Boomstick

New Member
#16
#16
That, and if the piston is slapping around in the bore, it will eventually grenade.

Set it aside for prep work so that one day you can build a real monster (hey, you can sleeve it down the road if you want!). No sense in wasting an engine that can be made right!
 
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