B+ seizure

[relic]

A couple of weekends ago I hauled my B+ to an event in Port Hope Ontario put on by the Canadian Vintage Motorcycle Group, of which I'm a long time member. The Ganaraska 250 is loosely based on the Moto Giro type rides and is aimed at small displacement bikes although larger rides are allowed as well. Its about 250 kilometers, broken up into a morning and afternoon ride on secondary, sparsely traveled roads, for the most part paved. Its a timed run based on a 30mph average and points are lost for arriving early or late at the check points and getting lost is a common occurrence. There are also four "agility" tests included where you can lose points for hitting the cones, dabbing a foot and also timing. In all I was looking forward to a great day aboard the only Hodaka in attendance. Did I mention it was a 6.5 hour drive to get there?
This was my first time to make it to the event so I was a little nervous doing the first agility test with several folks watching, waiting their turn but I cleaned it and rode away breathing a sigh of relief. And mistakenly thinking I was in for a good day.
I managed to navigate my way through the first six miles, (instructions were provided for route sheet holders or tank bags) but at the 6.4 mile mark my B+ decided to seize up.
I've mentioned it on the forum before but to refresh-over the winter I installed new crank bearings and seals, new Wiseco piston kit and had the cylinder bored to 2nd oversize. I did a very gentle break-in and had over 300 miles on the engine before it seized at this ride.
Positions were based on registrations and it worked out that I was near the back of the pack so I was only on the side of the road for about 5 minutes when the chase truck arrived. Decision time---I stood there in the rain, (yes it was raining of course) and thought about it. I could let the sweep truck go on and wait it out hoping the piston would free up and she'd run again. But I was worried about the possibility of doing more damage and I figured even if it did start I'd be stressed the rest of the day wondering if it would last. So I elected to accept the rescue and we loaded the Hodie into the truck. They brought me back to the event HQ, I loaded it into my trailer and 7 hours later, I was back home.
Top end apart and there is no sign of lean running. Of course I'd done several plug checks since the first start and all were about as perfect as I could ask for. What I found was a typical "four corner" seizure along with stuck rings. I passed the ball hone once up and once down in the cylinder, sanded the high spots off the piston, soaked in in ACF50 which quickly free the rings and with a new circlip and base gasket I assembled it.
Started first kick and seems none the worse for wear. No new rattles, same power, in fact I've ridden another 50 miles since.
I half expected to see this happen during my break in but after 300 miles I thought I was safe. I wasn't being any harder on the bike during this ride than at other times so it came as a surprise.
Its all fixed up and I expect it will be good now and for a long time. Its just too bad that it happened when and where it did. I was looking forward to the lunch and supper that came with my entry fee.



Ken

[Bill2001]

Following, with interest.
Seizure is the odd problem with these vintage 2-strokes. I'm looking for ways to reduce that Walk of Shame.

What premix oil and ratio were you using?
What was and is the piston clearance?

[Bullfrog]

. . . and I'd like to add one more question. Was (is) the piston pin a "thumb push fit" into the piston?

Ed

[Al Harpster]

Is the scuff you show on the piston the only one, or are there more?

Al Harpster

[RichardMott]

I might have missed it, but what was the altitude difference between your home and the venue of the ride? My concern is if your mixture might be too lean. That would cause a condition that might cause seizer.
Just my 2 cents

[Hydraulic Jack]

What is your piston skirt clearance set to? How fast were you going when it seized and how long did you warm it up before you started the 6 miles you completed? Was the gas a fresh batch of premix, or an old tank of gas? What premix oil do you use and at what ratio? Was it raining hard enough for water splash to have chilled the cylinder?

Since you recognized the type of seizure you had, you likely already know what causes such seizures. Most often described as the piston heating faster than the cylinder, I think heat differential is relative. Whether the piston heats faster than the cylinder or the cylinder cools faster than the piston, the result is the same, and here you may have simply shocked the cylinder on a hot piston.

Simply said, four corner seizures are the single biggest reason I don't care for Wiseco pistons, particularly in air cooled engines. Wiseco pistons are heavier than the original Hodaka cast piston, and most of the extra material is in the wrist pin boss. If this piston was set up using Hodaka Art clearances, it is probably too tight. Over the years, Wiseco has changed the design of the plugs that are used to machine Hodaka pistons, so recent manufacture is probably better than older stock. If this was a left over old stock Wiseco made years ago, I would replace it. If you can find either a two ring Art or even a one ring super rat Art piston, I would use those before a Wiseco. If you are going to stay with the one you have, did you verify clearance and write it down? If so, what is it, and what was the clearance recommended by Wiseco, usually printed on the box it came in?

The other consideration is the one mentioned by Ed. The question of thumb press fit wrist pin has to do with distortion of the pin boss by a too tight wrist pin, although if this were the case, I would expect you to have had your four corner event before 300 miles. Still, it is a fitment issue that must be addressed in every rebuild. I have not yet seen a Wiseco piston that needed the pin boss lapped to fit the pin, but I have seen almost every Art piston need a bit of dressing to fit the pin. This might suggest that Art cast pistons are more prone to four corner seizure, but they aren't, because the pin boss isn't as built up as Wiseco, and the Art pistons are cast, not forged. On the other hand I have never deliberately built an engine with an Art piston with a tight pin just to see if it would fail, so I don't have empirical data on that point.

Bottom line, check clearance, verify premix.

[Al Harpster]

Sorry, I failed to read carefully that it's a four point seizure.

Looks just like my modern Wiseco ace 100 piston a couple weeks ago. Four Points. Believe yours is a 'modern' Wiseco piston shown.

My bike had plenty break in and ran fine at say 30-35 mph. When I tried for 60 it locked up.

Very unpleasant. Back tire squealing, cars around, poor handling.

Cooled off in minutes (or less) & started right up. Ran fine at rational speeds & got me right home.

Upon closer inspection I figured I had not left sufficient clearance when I honed the cylinder to size for my plus .020 piston.

Sloppy work on my part. I thought I had .002/.003 clearance, but re-measuring I think I may have been as low as .0015. Or even a bit less in some areas.

I have now honed to plus .003 or a bit more as best I can tell measuring with a bore gage. Have not started it since so I can't tell outcome. I'm a bit scared to try the speed run again.

I don't think the brush hone is going to do it for you if your cylinder is too small. I use a Lisle 16000. Pricey, but more like a real cylinder hone.

I use that "solid" type hone and a (cheap) Chinese dial bore gage that's set to size a by a (cheap) Chinese micrometer. The micrometer is locked to the largest diameter I can find on the piston skirt.

I'd make inquiry into the shop that did the bore work for you. Take the piston and cylinder back for a re-measure.

They may not like it coming back, but you will want to have an accurate measurement to determine clearance.

Til you get that measurement you can't rule out bad sizing.

That's my take an I'm stickin' with it!

Al Harpster

[relic]

Lots of replies, sorry I'm at work all day and only have access and time to log on in the evenings.
I'll try to answer all the questions posted; thanks for all the interest/comments etc.

I'm mixing between 20 and 25:1. (40-50 mili-liters to one liter of gas-sorry for the metric measurements but that's how we purchase gas and oil products here so I've converted myself over the years) The gas is fresh. In Canada I don't recommend you keep gas more than 30 days. At the shop where I work we deal with stale gas every day, it makes us lots of money.
I feel the air/fuel mixture is good, based on plug readings and "seat of the pants" running. This is my first Hodaka but lots of two strokes in my fleet. I don't mean to sound like I think I'm smart at this but I have rebuilt several and have lots of time working with Mikuni's etc.
I know the rep of Wiseco's and I've had this exact same situation on my DT400C that I had a Wiseco in for about 5000 miles. But it happened on the first ride after that rebuild, not after so many miles. I've since had the Yama cylinder sleeved and fitted an NOS stnd piston. Another 3000 miles on that one since.

My Hodaka cylinder was bored to .0025" clearance, done by a very competent machine shop that we've used where I work for years. I sent them the piston and cylinder together.

Piston pin was what I would call just beyond thumb press fit. I have small thumbs, hahaha so I usually push them in using an appropriate size 1/4 drive socket and the palm of my hand. Before, I put the pin in the freezer for a few minutes while I arrange things. That said there was some bluing on the pin after the seizure, going back together was the same as the first time.

Altitude would be pretty much the same between home and the event. Less than 1000ft and probably both locations around 600 I think.

As far as this particular day went: my start time was 9:17am. I started the bike at 9:10 and slowly moved up the line waiting my turn to enter the start block. At the appointed time I was allowed to run the agility test which was weaving between pylons for maybe 50 feet; time to complete was 10 seconds. I don't know how long I took but you get the idea. From there I was out onto the streets and navigating through residential area with speed limits of 50kph (30mph). After about 3-4 miles of this sort of running we had a mile of 80kph (50mph) to do and I was watching my speedo and tach, conscious of not over doing it. My speed was around 45mph. Next the route sent us onto a rural farm road where I was running between 40-45mph, climbed a hill where I had to drop two gears and then once on level the bike seized shortly after upshifting. I can't recall whether it was in 4th or 5th when it quit.
The rain was between a drizzle and steady, not pouring. Yep, puddles on the roads but I don't recall any that were real splashers. Might have been though.
So...I think I gave the bike a full warm up before working her harder.

But, for sure it experienced what we call at the shop a "cold seizure". On snowmobiles we call this an ice shack seizure. Guys will be ice fishing and decide to ride over to their buddie's shack to say hi. Jump on their snowmobile, light it up and pin it. Sometimes they make it, but often we see the results on Monday morning.

Regarding piston availability- I would have liked to buy an original but I needed at least a first oversize. My standard piston and original bore size cylinder had about .007" clearance. I tried SH but they had nothing to offer other than 4th over in stock. I couldn't see taking a barely out of spec stnd cyl and boring that far over. I purchased this Wiseco through a forum member. I believe its a new style Wiseco. It didn't come with the usual Wiseco paperwork specifying clearance etc.
I didn't measure the clearance before reassembling this time. Suffice to say its now larger but the engine sounds the same, no slap or rattle.

All in all I think Jack is on the money regarding Wiseco pistons and what happened. I've experienced this before and I've read and heard lots of the Wiseco reputation. One of my coworkers in the shop jokes that this is a "racer's break in". Run hard, seize it, sand off the high spots and she's good to go from then on.

My biggest regret is that it happened at this ride. Far from home and surrounded by many cool vintage bikes, Norton's, Honda's, Kawa 2s, Guzzi "bacon slicer" Falcone and even a Panther.It would have been cool to finish on the small displacement Ace. Maybe next year...

Thanks everyone!

[Bullfrog]

I have zero direct experience with the Wiseco pistons . . . have couple on the shelf but haven't had to press them into service yet. So my concern may not be correct, but if you freeze the piston pin, then have to do a relatively high effort, socket assisted, palm push of the pin into the piston . . . that is a looooonnnnngggg way from a "thumb push fit" (with all components at room temp). I could be wrong, but I think the tight fit for the piston pin is cause of the seizure - and if it were in my garage, I'd tear it down and adjust the piston pin fit before riding further.
Ed

[Hydraulic Jack]

Relic,

Thanks for the quite complete rundown on your situation. Clearly you are not a stranger to two strokes.

Wiseco has a chart showing common clearance, but the box it came in should be the preferred source of info. I think even Wiseco doesn't publish specific clearances for specific pistons. My recollection for a 54mm piston is that .0025" should have been within reason if on the tight side of the clearance needed (roughly .001" per inch of bore) and your coworker is probably right, that having now buffed out the scuffing, you may never have a repeat.

Ed is also right that if you have to freeze the pin to push it in, the hole is too small for the pin and the piston should be relieved until the pin presses in and out with no tools. Where on the pin did the blueing appear? If under the bearing, I would say it got really hot and I would wonder why. If in the pin/piston interface I am surprised, but still it shouldn't be blue there. It well might have worked back and forth until too hot to move, at which point a swelling pin could interfere with the piston. I suppose that might cause a bit of blue, but steel blues at something like 600 degrees or so, so bluing isn't a good sign on the pin.

Give thought to pulling it down one more time and dressing out the pin hole until the pin is a nice hand press fit. I use either a piece of dowel with a split end and a strip of W/D 220 or finer, or a small socket of appropriate size, done by hand only, no drill motor, and do it wet, not dry. A little at a time and it won't take much. When done, with the pin lightly oiled, it should press in with a finger push and move cleanly. Over the life of the top end, the piston pin must be able to rotate in response to reciprocating action so that oil is constantly distributed and so that the rod bearing has a new surface to run on constantly. As far as a hot pin swelling more than the aluminum piston pin boss and stressing the boss or causing seizure, I would say it is possible but unlikely given the relative rates of expansion of steel versus aluminum. More likely is the pin boss swelling faster than the pin, but the result would be the same, i.e., an interference fit. At that point the pin would stick and stop rotating. Still, it would be the swelling boss area in response to heat that would cause the seizure, not the swelling pin IMHO, and once stuck in place a non-rotating pin stops making heat. Absent scientific data I would continue to doubt that pin fitment in itself causes seizures.

If you do take it back down, measure the skirt clearance with a feeler. I don't use micrometers for this because of reading errors. It takes skill to use a micrometer in a cylinder, but a feeler gauge will always give you an honest, if slightly conservative, answer. That is, if you come up with two thousandths with a feeler, it could be two and a half thousandths, but won't be less than two.

Passing curiousity: with 300 miles on the piston, what did the skirt and bore look like? Could you still see any hone marks on the bore and was the skirt still showing mill marks?

[Darrell]

Have you measured to confirm the .0025" clearance? I specified the same clearance at a shop last year -- what I got back was actually around .0015".
In my case, maybe the machinist was measuring from top of the piston, rather than the skirt.

Is there a possibility some machinists try to ball hone a cylinder to the new size rather start with a boring bar? The former seems a rather imprecise method.

[relic]

Ed, great info. Thank you. I didn't feel it was tight based on others I've done but this is the first of this small a size so I should do as you say and revisit the pin fitment. When I ordered some new circlips I didn't remember that they come two to a pack so I now have plenty on hand.
Jack-Regarding the coloring on the pin, it wasn't in the small end bearing area. Thinking about what you are saying temp wise I'm now wondering if it was just marking from hot oil. I'll check better when I pull it apart.
I too like using a feeler gauge for clearance checks. We've each got our own bore gauge at work and when we have to measure a cylinder, we each take a turn using our own equipment, then switch and then compare notes.
Darrel, the machine shop we use is a huge operation, CV Tech is their name in Quebec. If you check their website you'll see what I mean. They make their own line of parts- clutches, performance stuff etc. Not your run of the mill local shop. Now, anyone can make a mistake but I've yet to have anything come back from them less than perfect. But---I didn't measure before I did the first assembly. Guess I'm used to trusting them. I think if my clearance was anything less I would have seized her long before I did.
I don't think you could ball hone a cylinder accurately to another size. Playing around with my own stuff over the years I have used a rigid hone to add some clearance but its pretty hard to end up with a straight cylinder. It ends up somewhat barrel shaped, (larger in the middle than at the ends) if I recall correctly. I guess because the hone spends more time in that area than at the ends as you move it back and forth?

Ken

[Bill2001]

Good discussion. Maybe we'll get a handle on the seizure issue some day if we keep working the problem.

Readers may want to do a forum search on "four-corner" and "four corner" to find other discussions on this topic.

K&S sells packs brass shim stock from .001 to .015, and the sheets are cuttable to convenient widths. I use these feeler.gauges to measure piston clearance. When we honed my cylinder and fitted the new piston we ended up with a clearance of .004. At the time I thought this was too loose, but it may be a good value.

Instrumentation I have on the WBat-94 is an EGT gauge. The exhaust gas can give me an indication of the mixture at a steady throttle opening. This correlates with a piston temperature and the possibility of seizure. I am using it to evaluate the jetting and it has already saved me from running lean. This is a work in progress, and I'm taking notes.

Later on in the season when there is more free time I plan to run the Hodie on a dyno and check the correlation betw. mixture, EGT, etc.

[Al Harpster]

"racer's break in, Run hard, seize it, sand off the high spots"

I sort of followed this procedure the FIRST time my modern Wiseco piston seized in my Ace 100.

I polished the piston score marks with fine grit sandpaper, gave the cylinder a quick hone, reassembled, pressure tested and figured I was OK.

You may have better success than I did.

The SECOND time it happened I thought to re-recheck the clearance. I found it was markedly smaller than I'd thought it was.

You may be in good shape with a "Racers break in", and I may still be locking mine up with ~.003 to .0035 clearance next week.

Rear wheel lock up street riding in traffic is my new concern. I've added it to being seen, looking out for the other guy and keeping my distance.

Al Harpster

[relic]

You maybe right Al. My plan is to take it apart again, check the wrist pin fit and check the clearance at the same time. This won't happen for a couple of weeks but I'll post my results when I get to it.
And good luck with yours; hopefully your troubles are over.

Ken