Model 92B Top End Woes

[brad100]

After several days of carburetor tuning, running rich, a gutless power band, swearing, and praying- I finally cracked into my top end.

Yikes. I’m looking at a +7 bore and an unknown piston size or rings.

While trying to carefully remove my bottom ring for cleaning and measurements, it snapped in half. Doh!

I need advice. How do my cylinder walls and piston look to you? I cleaned the top of the piston with a soft wire brush, and was able to get it feeling pretty smooth with very minimal pitting. The walls of the cylinder look okay to me, with no deep gouging (or any gouging).

Kinda need my hand held as this is my first time messing with pistons, rings, bore size, the whole 9. Should I just purchase a set of piston rings for the 92B from Strictly Hodaka? Do I need a shiny new piston with the rings? Too far gone and it needs a new bore, piston, and rings?

Here’s some accompanying pictures. Apologies for the random order. Tried to document some before and after if the cleaning thus far. If you guys need pictures of anything else, I’ll be happy to snap em!

PS, this small flat ring was underneath the bottom piston ring. I haven’t seen it referenced anywhere or in any schematics- thoughts? Also, check out the “Ace 91” marking on the connecting rod!

[ossa95d]

Brad,
Sometimes what seems obvious to those of us that do this a lot might not be so obvious to a first timer. When removing the rings you carefully expand the ring just enough to slide off the top of the piston. I noticed that the top ring is still on the piston. It would be more difficult to expand the bottom ring enough to clear the top ring so the top ring should be removed first. Looking at the flat spring that was under the ring it looks stretched as if it may have been removed by pulling it sideways off the piston. The ring definitely wouldn't survive removal in this manner. Also as a side note the person that assembled your engine may not have been aware that it's recommended to install the circlips with the gap and tang either at the top or the bottom so that it won't compress the gap when reciprocating at high RPMs. Your cylinder bore does look like it's in pretty good shape but it would be difficult without measuring piston clearance and ring end gap to tell if it needs to be bored or the piston and rings replaced. All the right people are on this group to help you through this project. Good luck!

[Bullfrog]

That "7" stamped into your cylinder indicates that the original standard bore had been precisely measured/gauged and found to be in the "7 class", so the assembly worker could grab a "7 class" piston (which had also been precisely measured/gauged to establish its size class) and install it - and KNOW that the piston-to-cylinder clearance was correct. So we don't really know what size piston you have till you measure it. That "7" was useful exactly ONE time - it provides NO useful information now.
Ed

[brad100]

Thanks for the advice so far guys!

Ivan, it was a long day with a skipped lunch and too much black coffee- I unfortunately wrestled the bottom ring off first. I attempted to pull it straight back and off the track if that makes sense (it doesn’t). I figured the ring would have some flex to it (again, it doesn’t), but I outta quit assuming stuff. The flat spring made the exit off the piston that I had planned for the bottom ring, but I guess I stretched it out of whack now..jeepers.

Ed, they like to make us work for these bikes huh? I think my first order of business is getting a set of digital calipers so I can take my measurements. I appreciate the history you shared- while the +7 might not be of any help, your information sure is.

[thrownchain]

Caliper will get you in the ball park, but to be really sure someone should measure the piston with a micrometer and the cylinder with a bore gauge or similar accurate tools. You're looking at clearances in thousands of an inch. And measured at several different points in the cyl to measure out of round and taper.

[brad100]

Thanks for the tip thrownchain! I’ll be sure to pick up some telescopic gauges when I make my Harbor Freight run tomorrow. I watched a pretty helpful YouTube video where the guy made measurements on the x and y axis of the cylinder and at top, middle, and bottom of cylinder for 6 measurements in total. Seems a pretty accurate way of checking clearance inconsistencies.

https://youtu.be/60-WtFZj8AQ

Upon further inspection, I do indeed see a 7 on the piston adjacent from the arrow. So at least I can make the assumption that it’s the original piston, matching with the +7 cylinder.

I was also able to locate a capital “N” on that bottom piston ring that I beat up. Does that ring any bells?

Finding rings for the Model 92 Ace 100B seems tricky. I’m seeing some oversize ring sets though none for standard, and I’m not ordering without measuring first- just seeing what my options are. Assuming I’m at standard bore, piston, and ring size- what are my options if a set of standard rings can’t be found?

I’m usually pretty resourceful with the forum search bar, but “piston, ring, bore, Model 92, Ace 100B, top end” and any combination of those words are all too common a phrase.

[thirdstone]

No one has mentioned the piston. I`m betting you need a new one, it looks like its been slapping around.

[thrownchain]

Plan on a bore, hopefully 1st over will clean it up. When you're checking specs remember there will be added clearence when you hone it if you only want to rering it.

[brad100]

What would my piston and ring options be if I went with a (hopefully) 1st over bore? Seems that piston and ring set would be even trickier to track down.. Again, sorry for the newb questions. I’m late to the top end party, but I brought chips.

If no boring is needed and I’m at spec, I think I’d still like the piece of mind of a shiny new piston to accompany the new rings.

Harbor Freight opens in a few so I’m making my way there early for my measuring gear. Should have measurements to report soon.

I’ll snap a better picture of the cylinder in sunlight today for us to gawk over.

[thrownchain]

You may have to put the word out to see if you can find a piston kit that would be the proper size. But first measuring what you have is the prudent idea.

[brad100]

Alrighty, got my measurements. I measured the bore with a telescopic gauge using the method described above, and took 6 different measurements.

50mm bore. My biggest spot is 50.12mm, but that is still within the max allowable wear. All other spots are hanging right around 50.05-50.1mm, so with that information I believe I’m at a standard bore with some wear?

Piston is measuring at 50mm. Top piston ring measures at 2.05mm high x 2.18mm wide. Bottom piston ring measures at 2.05mm high x 2.15mm wide. Top ring gap measured at 5.5mm. Unable to measure bottom ring..

1,153 miles on the odometer, but unsure of the previous owners riding habits. The history on the bike is that it was parked in a semi-insulated garage in the mid 70’s in Colorado. I picked it up sometime in September, and went through nearly everything but the top end. I could see some scoring on the piston head when the exhaust was removed and baked, but figured with good compression and an eagerness to kickstart, I was okay and those were just liver spots on the old piston. I’ve put about 10 miles on it driving it to work, and tuning the carburetor. Started running incredibly rich, and no amount of carb tuning was getting me where I needed. Then I lost power in first gear, and figured it was time to crack in to the top.

[viclioce]

Captain. Seeing as how the piston & cylinder are both still #7’s wouldnt that be an indicator that he still has a cylinder with a STD. Bore? I know the numbers have been explained in the past and again here, but as he first described it, he made it sound like it was a .070 over bore! Surely, this is a std. piston and the cylinder hadn’t been bored yet, correct? Just asking... Victor

[thrownchain]

Ok,next step, take your finger and go around the bore like your cleaning the inside of a cup, any groove you can feel is too deep and will need to be bored out. Bore should be smooth, any grooves will wear on the rings and piston. Like pits on fork tubes wear out the seals.

[thirdstone]

That bore looks reasonable for its age . I would take it to whoever you know that does re bores and ask them to run a hone through it to Clean it up. Once that is done Take a measurement with those telescopic gages and a Micrometer. Go from there. I would definitely fit a new piston and rings it’s just what size are you going to need .

[Bullfrog]

Vic - I've gotta stick with the recommendation to measure. To my knowledge "size class" indications were not stamped/impressed into the crown of the pistons - only ink markings were applied to the piston crown. So I don't know what is being seen on the top of the piston that resembles a "7". Whatever it is, it is not "findable" by me on downloads of the piston crown photos even with extreme zooms.
Ed

[Al Harpster]

There are two basic ways to go here:

1- Money is no option:

Send the cylinder to Hodaka Dave ( http://hodaka-parts.com/item.asp?cID=0&PID=10875 ) or someone just like him and have him bore, hone and supply a new piston. $220 plus shipping both ways. Say $270 total give or take. Maybe he will throw in a new base gasket.


2- Money is an option:

Try to find a set of standard piston rings for this standard Art piston. https://hodaka-parts.com. These rings are not currently showing on their site but they may have them. Probably email them or call during the call-in hours to see if they have them.

Clean everything up & put it back together. Maybe make your own base gasket from gasket material you can buy at Autozone or other.

$50 total plus your time.


OR (and a lotta guys gonna love this one)

No standard rings available? See if first oversize rings are available. File the ring ends til you get the correct ring end gap.

Clean everything up and put it back together.

Same $50. Better compression.

Your piston ain't no beauty, but the pictures indicate to me it could be an OK runner. My opinion.

Your cylinder is OK as-is if you want to go the low dollar route.


P.S. That's a lotta carbon build-up on that piston crown and piston skirt scoring for a bike with 1100 miles on it. I'm not sure that speedo was hooked up for it's entire running life.

Keep up the good work!

[brad100]

Thrownchain, I feel a very small amount of groove near the intake side, like a piece of debris made its way in. Not quite George-Clinton-bass-solo-groovy, but we’re in Earth, Wind, & Fire territory. Is very minimal grooving a bore or a hone job in your opinion?

thridstone, thanks for the tip. I do like the idea of having the cylinder shiny..

Ed, it could be my eyes playing tricks on me, but I’ll supply the picture. Hard to focus on it, and it’s not the same stamping/embossing as the arrow. I feel like I see a “7+” in the circled area.

Al, to the rescue. I have kept this project on the cheap side so far, and a $300 bore job would be $200 more than I paid for the bike. I know that I got pretty damn lucky with a $100 Hodaka. But being a 26 year old in college, cheap is my creed, my code. Any sort of solvents you recommend for cleaning? Will solvents clear up some old oil paths in the cylinder/make it shine again, or is that only achieved via a hone? I’m concerned about the carbon buildup around the exhaust port and valves, and want to eliminate the possibility of any of that buildup and gunk getting on the cylinder walls. Thanks for the tip on the rings, I saw that SH was only carrying the .03mm over but I’ll get in touch with Terry. Could maybe try my luck with those?

[brad100]

Fellas- reading more specs on the Strictly Hodaka site, I see that the Model 93 Super Rat and Model 90 Ace have a 50mm stroke and feature the same ring gap clearance as the Model 92B. Are these suitable replacements? My gut tells me yes? I see standard sizes and a few overbore sizes available.

[Al Harpster]

Only the rings for the Ace 100 piston will do. Standard or plus .010 only for the low dollar fix I suggest. Any bigger are no-go.

You can also try hodakapartsidaho.com for the rings. He's traveling, but says he will respond to inquiries.

Stains in the cylinder may clean up with solvent, but stains are not important.

Brake cleaner in the aerosol can will do your clean up work. Ask for the old fashioned formula at your autoparts store. It's got a bit more kick and shoots out a strong stream if you want to flush your ports. WATCH OUT. This stuff really blows out fast and hard. Glasses on please.

You can clean out the exhaust port with sandpaper. 100 grit or so will do. Your latest picture of the piston crown looks clean enough for a runner.

If you are concerned about 'crud' in the crankcase find a way to flush it. Lay the bike on it's side and blow it out with the brake cleaner. Let it dry. Squirt a couple table spoons of oil in after. Or if you have compressed air available, blow it out with air.

Clean it, re-ring it, reassemble it and go. That's your low dollar path to getting a crack at riding this thing again.

Keep the faith!

[thirdstone]

Brad if Cheep is your creed then we can get the costs down a bit more.
Buy some 400 wet and dry paper and clean up the piston by taking the high points off, use a cork sanding block and Kero or petrol. Same for the cylinder , remember remove high points only. If you have aluminium stuck to the bore you can dissolve the aluminium with Hydrochloric acid (muriatic acid) in about 5-10 minutes, It wont harm the iron in that time.
Base gasket can be made with cardboard from a Cornflakes packet or similar , that will save you $2.
Head gasket is another matter. I think you can anneal the Aluminium ones , Ed could tell you how.
New rings are a must I think and also re position the Pin circlips (as previously mentioned) so the prong is vertical, you can also snip half the prong off. Maybe someone here has some old rings they can give you. Its gonna rattle !!
And what Al says
Good luck

[ossa95d]

Brad,
I have been following this discussion and have to agree with Al. If you only paid $100 for the bike and just want to play with it as cheaply as possible, a hone job and new set of rings might do for now. Going back to your first post I doubt the jetting and power issues you were experiencing were related to the top end of your engine. I would suspect crank seals or plugged exhaust were the major culprits. Plugged exhaust is the primary suspect especially given the carbon build up you found. In the future it might be helpful to do a compression test and a leakdown test prior to disassembly. This will give you a better sense of the health of the top end and the seals and perhaps save time and money in diagnosing problems. It's too bad that the bottom ring got broken because it sounds like your top end may be usable as is. At least you're getting to know the insides of your scoot. I hope you're having fun!

[thirdstone]

I second the leak check.
Easy and cheep to do and great peace of mind.
Try and hold 6 PSI For a min or two. You can do it with out the cylinder on to check the crank seals. Only a few bucks work of pvc plumbing bits. If you are really on a tight budget you could not fit the $8 pressure gauge (eBay rubber ducky boat). Use soapy water to find an air leak from the left hand side, obviously the right hand seal is harder to see with the clutch fitted.

[brad100]

Al, thanks for the guidance. I see now that the Super Rat Piston has one ring as opposed to two, though identical specs, gap, clearances, and acceptable wear amount. Ace 90 has a 48mm bore, but 50mm stroke and same specs, gap, clearances, and acceptable wear amount as well. I messaged Terry this morning so thus begins our correspondence for the standard or .010mm Art rings. Brake cleaner and 100 grit sand paper are added to my list, and thanks for the description of blowing out the crankcase free of debris. From what I can see, there is not a whole lot of gunk in there to speak of. Just around the ports, on top of the cylinder head, the whole jug was pretty damn cruddy on the exterior when I purchased it.

Thirdstone, thanks for all of that to soak in, especially the pictures! Very nifty pressure tester there too. While I am on a budget with this bike and life in general, I do want to do this correctly. I’m not opposed to going to Harbor Freight again and picking up their cylinder hone kit for under $25 if that seems wise to you folks. I wouldn’t mind learning the skill, having the tool on hand for future jobs, and having a freshly honed cylinder. My frugality comes in the form of “dont pay to have the work done when you can do all of this for under $150 with the proper tools and an eBay link for these damned rings”. I plan on purchasing the gasket overhaul kit, but the cereal box gasket is something I’ve came across before and made me smile!

Ivan, I appreciate you thinking outside of the top end! My exhaust is good. I had a couple barbecues with it, the spark arrestor, and silencer- blew it out and finished the job with a flat black VHT high heat paint. My seals, I couldn’t tell you about. I think that very well may be it. A leak on my clutch side. Sometimes when cold, it would puke transmission fluid out of the breather. Like a lot of fluid. Wonder if that had something to do with a leak in the seal? I take it a leak in the seal causes transmission fluid to enter the crankcase and burn up, but wonder if it makes it puke out the breather too.. At $19 (that’s fine) for a left and right side crank seal from Strictly Hodaka, should this be something I change regardless, or is a leak down test still necessary? Any extra piece of mind I have when assembling it back together is great.

[thirdstone]

The the clutch side seal is a case split job ,located inside the crankcase. Your engine education just hit the J curve . Not hard really.

[brad100]

Oh crap. Looking at the schematics, it is clearly situated inside the case but that didn’t register with me. Is this in your opinion worthy of the leakdown test, or are there already telltale signs on the piston and the performance issues I was experiencing that we have a leak? Prior to this project, the only true experience I have with mechanical stuff besides basic car maintenance is rebuilding a couple of scooter carbs, changing out a scooter fuel pump, and changed a tire. This is new grounds for me for sure, but I enjoy tinkering with it nearly as much as riding it. Nearly.