oil migration

[Kels]

Ed,, good points..

I just want to clarify, that the stock pipe MAY be fine.. but if you have a silencer that is restrictive (like a spark arrested one would be) then you could have as big of stinger as you want--->> but stuff a banana in the tail pipe and the heat can not escape..

Try putting a Car muffler on the end of diesel exhaust system Or just a 3" exhaust system and see what happens??

It may be fine when cruising down the highway or around town.. NOW,, get on a 7% grade and floor it and watch you heat up the headers and eventually, hole a piston. Same goes for the MX bike.. what is fine on a shorter "pull" may be catastrophic on a longer WOT pull..

Hold your hand over a candle... you'll get the idea.. anything can be tolerated for short periods of time.. Prolonged "ANYTHING" is where you have to make accommodations ...

It is all about TIME!!! and how long the engine can tolerate a mismatch..

Just Ask Doug Gardner--> He's been wearing that head for 55 years and his neck just can't take it anymore!

[racerclam]

I'm with Ed its too Lean no matter what oil you are using , although I do believe the oil is crap . Danny and I have talked a lot about this issue. I agree with Kels about the small stinger issue will cause this kind of problem but the stock combat wombat pipe isn't in this classification and wont even allow the engine to run a very high RPM its a bottom and mid range pipe and full potential of even a highly modified engine would not be realizes with that pipe.

Rich

[hodakamax]

[quote="Bullfrog"]Max - may I suggest a more patient approach? Everyone on this chat group knows that you and I think the machine was lean on main jet. But I'd certainly have to say that I don't KNOW that . . . I think it, but I don't know it.

Hey Ed, Maybe Max is becoming a little cranky on this one. Here's the reason. I feel that the Forum is a place to help people. I have spent several hours researching, contemplating and typing on this subject since the first seizure of the bike and the report on the Forum. After I tried to explain it the first time I thought it was worthy of an article in our Resonator newsletter. The article was published and reviewed by the Resonator's Technical editor and former National Service Manager for PABATCO/Hodaka (Ed, who really is a clever guy!) who deemed it technically correct. Then I try to answer a question or at least give an opinion on the second seizure. I don't know but it appears that some in our audience are skimming or not reading what I say.

When I analyze a problem I always go first to the most probable cause. Since about 90% of piston seizures are caused by jetting issues and this engine has experienced its second one, its becoming more and more likely that this is the problem. I look at the evidence from the spark plug which is somewhat questionable after a hot seizure but does suggest lean. If the engine is only slightly lean as suggested by the plug (and Ed and Max) and is run at high RPMs under heavy loads for long periods of time we can expect a seizure when the over-heated lubricant fails. It's easy to start blaming things that it's not than looking at the evidence.

Kels has provided a plausible idea that this is causing the seizure. I never claim to be an expert because I try to continue to learn something with each experience. In our racing program in the past we built our own pipes. We tried stingers long and short, big and small and even inside the pipe. Engines ran better or worse and peaked at different RPMs but never overheating or seizing. Again I'm just going on past experience.

There comes a point when all or most of the evidence points to the problem. I'm not 100% sure but I've reached the 97% stage. I personally have decided at least from my experience (not reading it on the internet) that this scenario with the exhaust is probably not happening at least in this case or at least in my opinion.

This is not some rare event written about in questionable literature, this is the most basic tuning requirement in air cooled two-stroke engines that exists. Riding trails or puttering around the street leanness is tolerated by the engine but under extreme race conditions things are much different.

Belittling Max and mis-quoting him because he doesn't agree with something you read IS making him cranky. In life (I was told by some older person) there are the talkers and the doers, the readers and the hands-on people. I try to be the doer and the hands-on guy. Experiences are to be shared and not used to prove you are an expert.

Another opinion by

Max

[Kels]

Since about 90% of piston seizures are caused by jetting issues

Max, can you tell us where you get this statistical information? I can't seem to find any of these facts.

As for stingers causing engine failure..

Let me share some of my experience that pertains..

I can run brand "X" silencer on a stock engine and hold it to the bar on an extended pull without issue.

When I install this SAME silencer on a modified engine, the engine will fail on the 1st extended pull.

Pipe pressures have been measured and shown to have a significant increase or decrease depending on silencer design and construction.

Pipe pressures also increase with HP output.

Again.. restrict your auto's exhaust system and see how it reacts.. This is not rocket science but more physics.. Restrict your bike's silencer and the same thing happens..

I remember having to run a spark arrested pipe at National event at Donner's Pass (9500FT) way back and the bike ran very poorly.. Yanked off the arrestor after 1 loop and all was restored.. Of course, the officials were not happy and wanted to disqualify me..

Point being.. there are numerous reasons as to why an engine runs well or fails... Chalking it all up to jetting would be unjustified.. I am sure Danny will figure it out.. Could be related to that antiquated head design...

[hodakamax]

Question was, where are the statistics about 90% of piston seizures are caused by jetting issues.
Some things should be clarified. Our shop sold and serviced Maico, Hodaka and Bridgestone, all air cooled two-strokes. Our shop was primarily racing with a few street bikes. Shop records on repair and racing programs showed that most piston seizures were caused by two-stroke oil failure from over heating due to leanness. In my article in the Resonator on piston seizure, Ed pointed out that this applies to mechanically sound and maintained air-cooled two-stroke race machines.This is the type of engine in our discussion.

The other 10% was attributed to failures such as seals (which creates lean conditions) and other mechanical failures such as bearing cage failure. You could lower it to probably lower it to 80% if you counted stupid things like forgetting to add oil comes to mind, or old gas, wrong clearances and other mistakes such as too much compression or wrong timing. The list goes on. Perhaps we could even add restrictive exhausts.

Ed summed it up after review and concluded that I was correct in my assumption. I think Ed liked to say "most" rather than 90%. The article is in the Resonator, Vol 2, no. 17 along with Ed's comments.

Max

[Kels]

Max, thanks for the info.. So the stats you are using are based from a shop that was busy in the 1970's and 80's?

With that information , in mind, wouldn't you agree that technology AND troubleshooting, based on a better understanding of the 2 stroke engine, has come leaps and bounds since that air-cooled era?

The engine in question is from that era but the knowledge of the inner-workings of a 2 stroke has increased drastically..

You can apply this new "knowledge of operation" to the older engines as well.

Afterall.. many ,early era ,2 strokes did not even have expansion chambers... WHY? because the concept of this was not well understood back then... same with head design and porting.. what was thought to be "ideal" then is considered primitive today... See what I am getting at here???

As knowledge grows, the mind-set of the tuner and mechanic needs to adjust along with this new found knowledge...

[taber hodaka]

Well it seems to me there is a difference between research and development and racing. Point winners don't win when they have to push the motorcycle back to the truck. When you go to a bigger main jet use a good oil and change the silencer you could tell us the stinger fixed the problem?? My first expansion chamber was in the mid 60's and then I went to the pipe that looked like the rat pipe. We ran the amal on the 90 and it would run 5 miles on overwind but that was with the bad oils from the 60's. Run a chainsaw everyday wide open every day tuned with good oil and no melt down??. Go ahead change the stinger keep the same oil and jetting and prove to us we are wrong. Or use a proven oil, jet or tune the machine by a professional change the stinger and go have fun on overwind. I don't think the engine had a chance I cannot say poor oil I would suspect it but all considered the machine was lean ------------ Clarence

[Bullfrog]

Um, the person who requests "free" advice is the only person who gets to assign "value" to the advice received. And that is OK. We can't, . . . er, um, . . . shouldn't, demand that someone accept our advice as being the gospel to the exclusion of other good/well intentioned advice. There ARE extenuating circumstances in this situation. I for one would never expect anyone to peg the throttle and hold it there for extended periods of time, because I assume (what's that saying? To assume makes an a$$ out of "u" and "me".) that no one would mistreat an engine in that way. It COULD be that piston seizure has been the low cost "safety valve" failure for the way this machine has been operated. PERHAPS, an exhaust system limitation kept it from revving high enough to break the rod or blow the big end or break a ring or . . .

That guy Ed that you have mentioned did indeed review your earlier article . . . and found it to be generally correct and without generally harmful errors. He tells me that he still stands by that . . . especially that "most" part.

. . . an antiquated head on an antique motorcycle? How could that happen?

Ed

[Bullfrog]

Clarence:

One of the problems facing Danny is that he sends the machine out with rich jetting for the conditions at the time of the jetting . . . and the rider does not/(can not?) handle jetting tweaks to match current conditions. As Danny mentioned - and I think we all understand - he also has to "fix" the rider. NOTE: Chainsaws are designed for and tuned for full throttle operation, no one really cares about the transition from idle to 1/4 throttle or sustained operation at varying throttle settings from 3/8 to 7/8 throttle. But our antique motorcycles and carbs are asked to provide decent performance and throttle response at all engine speeds and all throttle settings . . . and some semblance of respect for the machine has always been a component of reliability.

So . . . while I still think "lean for the conditions" was the cause of the seizure . . . the extended running at WOT and MAXIMUM attainable rpm IS a serious issue and may be the true cause of the seizure (due to not having enough "stinger" flow capacity for that sort of running?). It would be inappropriate for me to demand that all readers accept my thoughts on the issue post haste. Who knows, changing the silencer might allow higher revving for extended periods -- possibly ending with a grenaded engine. Ouch. Danny has a ticklish situation to handle . . . I wish him luck -- and place considerable faith in his problem solving skills.

Ed

[hodakamax]

[quote="Bullfrog"]Clarence:



So . . . while I still think "lean for the conditions" was the cause of the seizure . . . the extended running at WOT and MAXIMUM attainable rpm IS a serious issue and may be the true cause of the seizure

Ed[/quote

REALLY good point Ed, abuse as in too low gearing and over revving are part of the"conditions" that we are talking about. The blame goes to too lean for the conditions but the conditions exceed the limit of that equation. I couldn't have said it any better myself! Maybe we should add that to the equation. I've been trying not to tread there. I do hate to blame people for abuse, it's their bike.

Maxie

[taber hodaka]

I would have to ask the rider how far ahead of everyone were you when she blew? If there were riders ahead it seems they would be abusing there engines more? My final jetting was with my engine completely wound out I didn't know any other way. So fun to pass the 250 bultaco and greeves on old country roads running the 90 on overwind ,I must go apologize to the old girl for never letting me down. Abuse to me is wound out in fourth shifting to fifth but somehow hitting third. In honesty to all It is a pleasure for us old ones to hear your modern stories using the tools of the modern era. I do not recommend you overwind your motorcycle or your banjo strings.

[hodakamax]

Clarence, are you still taking your cod liver oil soe's you won't have a seizure?

Heh Heh, Max

[dcooke007]

Been working on the bike today. Decided I needed to work more and talk / type less. Just prepping things for reassembly...clean gasket surfaces, parts, carb, etc..

What mods to the engine? Combat wombat engine with Strictly Hodaka / Wiseco super combat .040 piston, intake studs relocated and super combat reed assembly fitted with one piece reeds, 30mm Hodaka sl250 carb, standard point ignition with timing set to .094 inch btdc, intake port modified for reed valve, stock transfer and exhaust ports, nicasiled cylinder. 03 wombat head used to reduce cranking compression to 170 psi. I think that is all of it.

I would gear the bike for higher top end but Will was not running out of gear. He was in third gear, throttle pegged and going up hill when engine seized. He told me he was "on the pipe the whole time". Which means he was riding it like a peaky high rpm machine. The engine does run out well but it has very good mid range too.

My feelings are the solution is going to be a combination of things. Suspect the oil most and jetting second. I still think this engine may have lived with better oil. The exhaust is still a thought but if you change to many things at once you wont know what the fix was. I will address the spark arrestor even if the other items prove to be the cause. Might be some more performance there even if it is not causing heating issues. With me doing the testing I think I can prevent a melt down during discovery.

Danny

[junker2k]

I have to ask, What type of gas was being used with 170psi compression? Pump gas with that kind of compression may cause some heating problems.
Jack K

[dcooke007]

Jack,
Engine was tuned for 50 / 50 race gas and premium pump gas.

Danny

[hodakamax]

Hey Danny, a few thoughts after being sidetracked. First I'm getting some outside info that the Repsol 2-stroke oil has a low flash point. This could be a serious problem and exactly what I'm talking about. Leanness causes temperatures to rise and if the flash point is below 300 degrees this could cause a failure of the lubrication properties early on. Maybe its time to change to proven Yamalube R. We all know that works. Secondly, After looking at your slotted piston with the giant holes (all good) it occurred to me that this engine might benefit from a notch in the skirt. This allows for more intake through the piston. You might get slightly more intake along with more mix traveling through the piston to cool the exhaust side skirt. All worth considering. I really think the seizing problem will go away with richer jetting. More fuel, more oil and more cooling comes from running race engines slightly rich.

Max

PS--just dreaming here, but that engine might benefit even more with a 4 hole piston with lower bottom holes and angled upper holes. There's always turbulence involved in the upper slot when it makes that 90 degree turn.The lower holes are mostly intake and the uppers mostly transfers. On downward travel of the piston the reeds are probably closing between the upper and lower holes. It's been a long time since I plotted all this out and I could be off a few degrees. Don't take me too seriously until I look at a real cylinder and do some figuring. The piston you have is a good configuration in that there is lots of material between the holes. A 4 hole piston has a shorter life but probably more performance. If nothing else you could angle the upper slot to improve the angle of flow. That along with the notch might be a worthwhile performance gain with little effort. Again, just dreaming. If I have time today I'll sketch something.

[Kels]

After looking at your slotted piston with the giant holes (all good) it occurred to me that this engine might benefit from a notch in the skirt. This allows for earlier and more intake through the piston. You might get slightly more intake along with more mix traveling through the piston to cool the exhaust side skirt.

Max.. Danny's engine is a reed induction engine. The intake is done while the piston is well above the reed area and the reeds control the flow. Notching the piston, like you recommend, will do little to gain more intake charge via the carb.

[hodakamax]

OK, really crude drawing but this is what I was talking about. I must admit that I had a Combat Wombat but never modified it. All these ideas are pre V- port but I see no reason this wouldn't work to increase cooling and power. Maybe Rich (racerclam) will chime in in on this one.

Max

[hodakamax]

Kels, yet again you are not reading what I say and trying to make me look stupid. You seem to be the expert and listen to nobody. It's a reed valve? REALLY? I do not wish to communicate with you as you're wasting my precious time--adios.

[DGardner]

The reason I had for posting about oil migration in the first place was to try and pass on info that I have came a cross trying to get my wombat to live running at a high RPM for long periods of time. Like a lot of you I have been riding and racing from a very young age witch was about nine. I started racing in 1973 on a 175 yamaha later that same year I moved up to a 1973 maico 400 and that is where my love of maico's came from. My last year of racing modern bikes was about 1986 or 87. Then around 1988 I started to pick up old maicos to restore even before I had heard about vintage MX. In all that time I think my 1979 KX125 was the only bike that I stuck a piston on. With all this time running 2 strokes I thought I had it figured out 32/1 and 927 oil......I was wrong and I was just trying to pass on some info hoping that people would think about what oil and ratio they are running for there use. 32/1 and yamalube (or what ever oil your running) for MX.....probably a great oil and ratio. Run that same oil and ratio on the road with high RPM for a hour? I don't know. Bottom line is study out what oil and ratio you are going to use for the riding your going to do. This is some of my bikes over the years of restoring bikes and racing.

[hodakamax]

Doug, I used to be a Maico dealer and your bikes look REALLY cool. Brings back good memories!

Max

[DGardner]

Max...I really liked my maicos and have raced and rebuilt a lot of them. I would make all the aluminum parts on them in my garage by hand, tank, side plates,rear brake peddle, airbox, foot peg mounts. I also came up with a part that stiffened up the clutch and made them work like a clutch should.

[hodakamax]

As a dealer for Hodaka and later Maico, my sponsored teammate and I developed and raced Hodakas first. He finally switched to the Maicos and occasionally I would race a 400 Maico with him. After racing 100s for so long I was always amazed with the fire hose roost the Maico produced. It worked two ways of course, roosting someone and getting roosted! Thank goodness for duck bills and Jofa mouth guards. Great memories.

Max

[DGardner]

One more cool bike that I'm working on is a 1984 Heron RM500 center port (RM500 engine in a 84 RM250 frame). From what I understand there was only 6 of these ever made in the UK by Heron suzuki the suzuki importer. For a number of years I have wonted to build one and with the help of three of four friend I now have one. This summer I will pull it apart to paint and make a new tank.

[---]

After looking at your slotted piston with the giant holes (all good) it occurred to me that this engine might benefit from a notch in the skirt. This allows for earlier and more intake through the piston. You might get slightly more intake along with more mix traveling through the piston to cool the exhaust side skirt.

Max.. Danny's engine is a reed induction engine. The intake is done while the piston is well above the reed area and the reeds control the flow. Notching the piston, like you recommend, will do little to gain more intake charge via the carb.

Because it is a reed induction, intake happens throughout the up stroke, essentially 180 degrees. This would be the reason for putting holes, slots, and other magic in the piston skirt. Any removal of skirt that presents an intake path during the up stroke will enhance, to some extent, the ability to breathe. Trimming the skirt bottom as Max suggests hurts nothing and may to some small extent enhance intake. Reed valving interrupts intake charge loss on the down stroke, at which time neither the holes in the skirt nor the trimming of the bottom edge have a negative effect. The fact that this is a reed engine is neither here nor there as far as the question of whether trimming the skirt as suggested has added value. That the trimming of the skirt may have its genesis in an old piston port design is not, in itself, a reason not to do it. Not to mention that it also lightens the piston which, with a Wiseco, can't be a bad thing.

As for the chart on oil migration, without explanations of terms used and protocols used in gathering data, the data itself is of little value other than the generalities drawn. Such as, at idle an engine needs less oiling, and at full throttle it needs more oiling, and so one might want to adjust their premix according to most likely use. Well, heck, I knew that back in 1970. So did everyone else who was racing 2-stroke bikes. If the chart offers something else that might be new and useful, I missed it.