Super Rat (98) piston

[SuperRat01]

Hello all, I am rebuilding a (98) engine. I removed the head and cleaned the carbon off the top of the old piston and found the number "20" stamped on it. Does this number signify any thing? Just curious...Thanks, Linc

[olddogs]

+20 or 20 identifies it as an over size piston. This allows the new owner to get replacement rings without measuring the piston. Somewhere in its past life it was worn to the point the existing piston was too loose in the bore or it had been seized and caused damage to the cylinder liner. Very common in and older bike. Standard bore would be 50 millimeters. Every 10 thousands is .25 MM. Your piston should now measure 50.50 MM. If the piston is still good and the bore within wear limits, replacement rings are still available on this site or with a little searching.

[viclioce]

.020 oversize. You still have plenty of life left in that cylinder, even if it needs a re-bore. If tolerances are still good and piston shows insignificant signs of wear and/or damage, you can just buy new rings and put it back together. If piston shows damage or if ring gap is getting too wide, then a bore is necessary. ; D Victor

[SuperRat01]

Thanks Guys for the reply. That sure does clear up some things for me. I think the piston is in very good shape and the cylinder seems to be fine but I think it needs to be honed. Can one of you explain to me the best way to clean up or hone the cylinder ( I've never done this before). I mean like what is the procedure? Thanks, Linc

[olddogs]

there are a couple of different types of hones and a couple differing opinions on honing. A flex hone has multiple abrasive balls on a wire cage and a stone hone has 3 fixed blades. The flex hone just de-glazes the bore and a stone hone can do a little straightening of the bore. They will both put a cross hatch on the cylinder wall to aid in oil retention during break in.I lightly use a flex hone as we have highly modified cylinders with expensive porting modifications. we want to keep the tolerances as close as possible for as long as possible. Since we tear down every couple of races,if the cylinder looks good, we just re-ring.

You can find much discussion on proper ring end gaps and break in procedures by searching this forum.

[taber hodaka]

I might read too much into things but Victors comment on when a bore is necessary I question. A piston could show some damage and the cylinder may not need bored, Also ring end gap would not be a determining factor for me as I file my rings to fit. To me a bore is required when there is cylinder damage or the tolerance is beyond specification with a new piston or determined with measurements.

[---]

You say you think the cylinder needs to be honed. Why? Do you see something that stands out, or are you assuming it needs it but are not sure?

If the piston is in good shape, and if skirt clearance is still within spec, the only reason to hone at this point would be to facilitate breakin of new rings, and even then if the cylinder is clean, I have done cross hatch with 220 w/d and oil using my hands, no hone.

The problem I see in using a hone, especially if you have never done this, is you can easily take too much leaving the piston loose, you can damage the ports, or you can taper the bore. Tolerance is fairly tight on a 100cc. I would not assume a honing is needed unless you have a specific reason for it. Better to verify skirt clearance and ring gap, and go from there. Also, a photo of the bore would help.

[viclioce]

Taber, my remarks about the piston were specifically about the piston. Stating that if there was no damage to the piston, he could just replace the rings and move forward. You DO read too much into things. Piston damage and cylinder damage, while possible to be related, don't always imply one goes hand in hand with the other. ; D Victor

[---]

I think everyone is getting ahead of the discussion here. Linc says this:

I think the piston is in very good shape and the cylinder seems to be fine but I think it needs to be honed. Thanks, Linc

Why get into cylinder refurbishment methodology when for all we know, it is good as it is. All due respect, but Linc says he has never honed a cylinder before, which suggests to me that he likely also doesn't necessarily know when and why to hone a cylinder, especially if the bore "seems to be fine." No one is born knowing this stuff. Perhaps the comment is born from reading about honing bores before installing new rings and pistons, and thinking it is always necessary. It is possible that this top end could go back together without doing anything to it.

So I would like to see photos of the bore from different directions, and photos of the piston. We also need to know skirt clearances in three critical, areas -- top, mid stroke, and bottom stroke. Someone who has not rebuilt a two stroke cylinder before might need guidance on how to do this before we discuss ring gaps and honing technique, I would think.

[viclioce]

Well put Greg. That's where I was trying to lead him. If the cylinder has no notable marks and the piston isn't damaged, he could very easily slap a new set of rings on the piston and throw her back together. The request for pics is a good idea. ; D Victor

[taber hodaka]

Victor I am a fixer not a writer. Not checking piston clearance or suggesting to just slap in rings and throw it back together would not be my recommendation to anyone, you could break or damage things doing that. one box of trophies got thrown out. I was the hodaka dealer here in Montana for nine years. I know a little and am learning allot from all of you. Bull in china closet breakum things.-----------Clarence

[Bullfrog]

The following statement is pretty clear, but not good advice. I don't think Clarence read too much into the statement.

"If piston shows damage or if ring gap is getting too wide, then a bore is necessary. ; D Victor"

It would be good to match the detail of advice offered, to the level on the learning curve of maintaining Hodies one has attained.

Ed

[SuperRat01]

OK....When I was a teenager I was riding the Super Rat and the engine started making a weird sound. I parked it and started riding my Honda 175. I never fixed it or rode it again. So, the engine has been sitting since 1981. About 15 years ago, I took the head off to see what I could find out. The piston and head looked to be good but that is as far as I went. I put the head in a box and covered the engine. Recently I decided that I was going to restore it, I took the head out of the box and there is like a haze of rust on the cylinder wall. So that is why I thought it should be honed. (After taking the engine apart it turned out that the noise it was making back in 1981 was a bad crank bearing). Hopefully this adds a little clarity. Linc

[taber hodaka]

The super rat piston ring will break in really easy. If there is only a haze of rust I would remove the powdery rust with 300 wet or dry sandpaper, sanding by hand parallel to the cylinder not up and down. How worn was your piston ring, how well was it running back then? I would check the piston to cylinder clearance. I think post #7 by Greg's was good advice. I would make sure there are not sharp knife edges at all the ports. We all like pictures and pictures of the bike also. I have never honed a cylinder when I am only installing a new L ring on a one ring piston. With respect to all opinions ------Clarence

[ossa95d]

Clarence, I love that picture and the story it tells! Do the leather pants still fit?

[SuperRat01]

Clarence, the bike ran very well back then. The ring looked good on the piston before I removed it. This bike has very low hours. I wrecked it when I was 13 years old and spent 3 weeks in the hospital with several broken bones. So, the bike did more sitting than it did riding. I will try to post pics of the piston and cylinder tonight. Thanks again, Linc

[---]

Since the crank bearing is bad, (and do you mean the crankshaft main bearings left and/or right, or the lower rod bearing?), it will need overhaul anyway. Once the cases are split, use new bearings and seals in all positions. You can sand the cylinder in order to get a truer reading on skirt clearance. Whether the cylinder needs rebore will depend on your findings. If it is the rod bearing that's bad, I would have to ask how it got that way. Usually it is lack of oil in the gas, or improperly mixed oil/gas at some point, which very often compromises everything else in the cylinder, including piston, wrist pin, wrist pin bearing, ring, and possibly the left main bearing. It will have to come apart for close inspection in any event.

[SuperRat01]

Arizona, I split the case and removed all bearings. The bearing that was bad was the crankshaft main bearing on the left side behind the CDI. The rod bearing is good (no up & down movement), the crank itself looks perfect. I am trying to upload pics but I think the format has changed since the last time I posted a pic and I'm not having any luck, but I will keep trying. Linc

[---]

If it's just the main bearing, you could be back in business with a little clean up and maybe a new ring.