PN 993713

[matt glascock]

Hi everyone. Just a quick question here. How does one go about confirming the proper form and function of the oil line check valve (PN 993713) on an M99 Road Toad. An acquaintance of mine was just served up a giant helping of fried piston with a side of rings and the culprit turned out to be a malfunction of this valve. I have three bikes with functioning oil injection systems and Thunderdog cylinder/piston sets are getting pretty spendy.

[Bullfrog]

Um, and we know the oil line check valve was the cause of the engine failure because . . .? (color me semi-skeptical)

I'll try to poke around one of those check valves in the next few days. My memory suggests that it is a simple one-way, spring loaded ball and seat, check valve - meant to prevent oil line draining (either forward or backward) when the engine is not running. It could also be argued that it may be there to prevent inlet tract pressure pulses from pushing oil back up the line (but I don't think that is its purpose).

Ed

[thrownchain]

Even a one way check valve can malfunction, ask anyone who had a british bike wet sump.

[Hydraulic Jack]

For the check valve to have been the cause of a seizure, the valve would have to be clogged or stuck shut. If it isn’t clogged and if it isn’t jammed shut, it wasn’t the cause. I have to doubt the oil delivery port would be effected by engine pressure pulse in any significant way because it is outside the reed cage, and even if it weren’t, pressure would follow the path of least resistance, and would not be enough in any event to overcome a positive displacement pump. So I don’t think the check valve is there to stop air pressure. It is, as you say, intended to keep oil from draining back leaving an air bubble when the engine is off.

You might want to verify oil delivery from the pump through the valve. If flow is sufficient, then treat it the same as any other two stroke seizure. What was the rider doing at the time? How long since last overhaul? What kind of oil and how old? What kind of gasoline and how old? The usual stuff. Having an oil pump doesn’t preclude seizure, even if it is working perfectly.

[Bullfrog]

I'm not suggesting the check valve in question didn't have a problem. Sounds like it probably did - or it wouldn't have been blamed for a complete engine failure. But I AM skeptical that a check valve failure is indeed the cause of the engine failure.

IF the oil injection system actually IS the cause of the failure . . . I would expect that some other "fault" is the actual cause of the engine damage. Something like a hardened and cracked oil delivery tube or cracked oil tank (pretty common faults) or a faulty pump (extremely rare).

So . . . I'm back to my original question, what would lead a person to believe that an oil line check valve is THEE cause of a severe engine melt-down?

Still planning on fiddling with a check valve.

Ed

[matt glascock]

Thanks fellas. I looked into the details. The motor was overhauled 1500 miles ago. Usual stuff - bearings, seals, gaskets. Piston/cylinder tolerances spec on +6 overbore so top end was freshened with a very light hone and rings. Motor was leak tested after the rebuild and was air tight. Carburetor rebuilt with stock jetting. Oil pump confirmed functional and calibrated and new oil lines were installed. No oil leak so tank assumed intact. I looked at the top-end tear down. The rings looked to be melted into the piston as if fused and the piston was extensively damaged in a classic 4-corner seizure. The crown appeared "powdery" with no almost carbon and the plug was chalk white with a generous aluminum bedazzlement. I'm sure everyone reading this has seen the top end of a 2-stroke bike ran to death on straight regular gas. This is the picture I'm describing. The oil pump and associated parts appear intact but function can not be confirmed until he sources a new cylinder as the one on the bike is on a +6 overbore and deemed unsalvageable. Fortunately the head should be ok. We figured the check valve is at fault because we couldn't blow air through it (as if that was a legit assessment of function). It may be a nonissue in this case as he plans on ditching the oil injection and going to premix but I would like to know it this is a known issue with the check valve and if so, what can be done to confirm proper function. Does anyone know if this is a simple ball valve, or is there a light spring load holding the ball in check that is easily overcome by the forward flow of oil when the pump is operating? As always, thanks fellas.

[Hydraulic Jack]

Every two stroke engine failure I have seen that was attributable to running straight gas, it was the bottom end bearing that failed first. But I suppose lack of oil could be your problem here.

Most of the damage described could also be attributed to advanced timing and/or lean running on ethanol gas. Four corner seizure is usually due to inadequate warming of the piston before loading. Dead white spark plug isn't necessarily lack of lubricating oil since you can, and should, have a toasty brown plug in a four stroke engine. That is, the brown color isn't really from the lubricant, it is from the fuel. Remember, even when mixed right, the oil is only around three percent of the fuel mix, and sometimes less. So the bulk of ash colorant on a plug is fuel residue. White is usually a sign of lean fuel mix. Perhaps there is some junk in the carb bowl partially clogging the main jet.

As for the check valve, I assume Ed is right that there is simply a ball and spring inside. How much pressure is needed to overcome the spring, I don't know. I would not expect it to be much, but I would also not expect it to freely pass air, so you might want to recheck the valve.

Don't forget to verify the bottom end bearings and rod big end. If it really ran on straight gas, I would expect all fuel lubricated bearings to be done.

[Bullfrog]

Is it too late to do an autopsy on the check valve in question? In many ways the check valve is somewhat like the pilot jet in the carb. Both items are the very smallest opening in their respective assemblies - and therefore the easiest to plug up completely with extraneous grunge. And both items MUST provide proper passage of their intended fluid or disastrous results will come about. The valve should certainly pass pressurized air in the normal oil flow direction, and since it didn't, there is certainly a fault there. But I'm still curious as to whether the valve actually failed, or whether the valve got plugged by some extraneous undesireable material. NOTE: The end result is the same - dead engine. But the solutions to those problems are quite different. Simply replacing the valve is the solution in one scenario. But in the other, a full oil system clean out is dictated.

I THINK (<-- that's a BIG "I think" - meaning I'm not positive) the check valve has a light spring pre-load. . . . still planning on putzing about with a check valve as soon as I can.

MUSINGS: Since the oil pump is a positive displacement pump, it will build pressure in the output line which opens the presumed spring pre-loaded ball valve so oil flows into the intake manifold. However, if the ball valve is "welded" shut (or grunge clogged) I don't know how high pressure will build in the delivery line. It is probably too late to determine, but was there evidence of oil leakage at the delivery line attach point at the pump outlet fitting or at the check valve fitting? Or even . . . did the oil delivery line "inflate" and split? Repeat - these are musings.
Ed

[dcooke007]

The check valve is a spring and ball arrangement. The ball should unseat with roughly 4-6 psi. Compressed air from your air compressor should not be used to test / unseat the ball. To much air pressure can force the ball back inside the small spring coils or damage the spring. A Mityvac vacuum / pressure tester is the perfect tool to test this item. A really good check valve should unseat at the pressure range listed and hold vacuum when applied. You can get a good seat of the pants idea if the valve is working by simply attaching a length of hose and using your mouth to test. It is a relatively inexpensive part so, other than determining cause of failure, just replace it.

Danny

[matt glascock]

Hi guys. Thanks for the rapid response. I'll start with Hydraulic's comments. The entire motor will be re-rebuilt. Just for additional information, he had been at WOT for approximately 12 minutes and running normally before catastrophic engine failure so, in keeping your your suggestion, he anticipates multicentric bearing failure. The ignition system was rebuilt at the time of the initial rebuild 1500 miles ago and he always (for the past 40 years ) uses a TDC gauge and timing wheel to set points opening as opposed to buzz box/timing light techniques so I don't think an advanced spark situation existed. He's a pretty darn good tuner. He runs 93 octane non-ethanol pump gas. I will pass along the suggestion to clean the carb, but I have a bit of trouble attributing a carburetion issue to be the source of catastrophic failure in a bike that was running typically and well at the time the engine explodes. I'm pretty sure he knows that feeling of mechanical awesomeness a lean bike displays just before it blows up. Thanks Hydraulic.

Captain, I'm pretty sure he is going with premix. I, on the other hand will embrace your suggestion to do a complete oil system flush. The lines were new, but there was just a few cc's of oil in the oil pump cavity on the clutch cover so there may have been a bit of back pressure resulting in a local leak. Convincingly, no major failure with the lines and no obvious (visible) issue with the pump. I'm currently in possession of the check valve so if at all interested, I could make arrangements to send it to you for examination. Many thanks, Captain.

[matt glascock]

Hi Danny. Thanks so much. I just noticed you weighed in on this matter and I appreciate that. Our superscientific testing method involved just blowing into it by mouth. Its very helpful knowing what the appropriate testing specs are. I completely agree with you regarding replacement and plan on doing just that. I've also learned along the way that a 40+ year (new) old part comes with no guarantee of well-preserved function. Therefore, your suggestion provides a decent confirmatory function test prior to replacement. Excellent, and thank you! I have a few in my parts stash but am wondering if its worth fiddling with them seeing as how a new one is really quite reasonably priced. Let me ask this - can you check the spring compliance and ball valve function by inserting a probe into the tube attachment flange to see if the ball moves freely? I'm thinking that this part should be added to the list of items for routing, preventative maintenance and inspection. Thanks to all!!

Best,

MAtt

[Hydraulic Jack]

I would think that, no, you can't test function with a probe. Danny's suggestion of using a tube and mouth is the way to go, because you can verify both passage (which won't feel exactly like free flow but will pass pressure when working-the hole is pretty small) and vacuum, and do it easily. Poking with a probe might end up like too much air would, and wouldn't tell you anything more than that the ball moves when pushed.

12 minutes at WOT??? And it blew up.....

[Bullfrog]

Twelve minutes at WOT!(?) . . . it does seem like a significant new contributing factor may have just come to light. While it might be safe to assume that enough safety factor was built into the oil delivery curve to allow continuous WOT operation, it might not be safe to assume that. I wonder, had the machine successfully survived previous rides with such long WOT periods?

I'm still skeptical that the check valve was the cause of the failure - unless it plugged up. Seems more like a massive heat spike due to detonation - which may, or may not have been brought on by reduced lubrication. (2 cents, well after the fact, long distance) I'm curious, what is the application requiring 12 minutes at WOT . . . and which presumably was trying for more time than that at WOT? Do we have a feel for engine operating speed (RPM) when the engine blew?

If planning on future use for extremely long periods at WOT, it would be appropriate to run oil rich pre-mix (say 20:1). I don't know what ratio the oil pump provides at WOT.

Ed

[matt glascock]

Highway running . I don't think I've held one at WOT for that duration but I'm sure I've done a solid five. I see what you mean about using a probe and possible associated damage. Good point. Thanks Jack.

[taber hodaka]

Bigger main jet. Lean on the top end, too much air not enough fuel. Sounds like the tuning was close. I tune for WOT just under the rich side with just a touch of blubber. Well tuned for mid range will let you touch WOT but if you are going to hold it open for twelve minutes you would have to be tuned for wide open. -------------Clarence

[Hydraulic Jack]

Ed and Clarence touch on good points here. I would start with the assumption that no Hodaka was ever manufactured with the intention of running throttle pegged for any length of time, much less 12 minutes, but if that's what is needed, one must necessarily build for that purpose.

For example, not knowing how much oil is delivered at full throttle, one would need to find out, then estimate the volume of fuel consumed over a period of time so that fuel/oil ratio could be estimated. Those who have raced two strokes at full throttle (Klemm Racing) will tell you that where 40:1 or 30:1 might be fine for most things, running wide open demands more oil. 20:1 is what Klemm suggests, and without really knowing, my guess is that the Hodaka oil pump won't give you enough oil to achieve that.

Then there is carb jetting, which would need to be redone anyway if running 20:1 fuel, so the stock jetting will almost certainly be too lean for wide open running with a sufficient oil load. So perhaps what happened here wasn't a failure of a single part, but a cumulative result of several things being pushed too far.

Rather than run 20:1 all the time, which might be tedious around town, it might be necessary to run both the pump and premix, and fiddle with the balance until you get enough oil at full throttle to protect the engine while still being able to run around town without a pocket full of spark plugs. This might require custom curving the pump, but would certainly start with determining just how much oil the pump can produce at full throttle and top rpm. This is like building a Daytona machine out of a campus transporter. It will take some doing.

You might also want to consider backing off engine compression a bit. Running compression builds with rpm. If the cylinder shows 170 psi in the shop, it will likely have around 200 psi when fully stoked. This might be too much for modern 93 octane pump gas. So you might have to back down a bit.

You should probably also do some combustion chamber mods to mitigate detonation and be very careful setting ignition timing.

Even though this bike might only be used on the highway, running full throttle for more than 90 seconds is taking it to an edge it probably wasn't built for. I don't think I have ever run a street bike at full throttle for more than two or maybe three minutes at most, and that was on a two stroke twin with a reputation for speed. Twelve minutes at full throttle is way more than a GP racer would see on a bike set up for full throttle.

Another thought would be to change your gearing a bit so that you can't get full rpm out of fifth gear, and then ride within the bikes inherent limits. I used to see 110mph out of my street twin, but as I said, never for more,than a couple minutes at most. At highway speeds, it was just loping down the road. The 99 wasn't made for highway cruising, even if it can get to 65.

[matt glascock]

Hey fellas, I talked to Jay (owner) for more background. Nothing really new to add other than he has ran the bike dozens times at WOT for just over 20 minutes which is how long it takes him to get to the place he trails. Its all 2-lane highway and to be absolutely precise, there is one turn about five miles from the riding land where he has to slow down to make the corner then right back to WOT so there is a little breather at that spot. Captain, he runs the bike absolutely stock including timing, gearing, jetting, and exhaust. He has no tachometer and goes about 200# in full gear so I'd be surprised if the motor spins seven grand. I confirmed his intention to convert to premix but will pass along your suggestion to go to 20:1 and rejet accordingly. Thanks Captain! Hi Clarence, I'm going to take both the Captain's and your advice and retune my Ace 100 for highway cruising. I have a new gig coming up and its 12 miles north of here on similar 2-lane highway. I plan on commuting on the Ace. I'm going 20:1 and MJ tuning to "just blubbering". In the meantime, I think the oil pumps are made by Mikuni. I am going to do a little research to see if I can confirm flow rate specs. Thanks fellas!

[Bullfrog]

Might want to take the 20:1 recommendation under advisement - I was assuming some sort of competition or dyno-run thing at 9 - 10,000 rpm continuous. Of course the 20:1 mix will lube well.

There is a history of things working with existing jetting and oil pump . . . until it suddenly didn't work. Gotta wonder why.

It sounds like oil lines might have been replaced . . . prime time to get some sort of extraneous material in there. I'm still interested in a forensic review of the check valve.

But probably more focused on things like . . . were all the previous road trips during summer temps and New England humidity? And the fateful trip on a 30 degree day with low humidity? (Lean jetting.)

Ed

[matt glascock]

Hi Hydraulic, we were posting simultaneously so I missed the opportunity to process the points in your post. Thank you. You bring up some excellent points. I've set the calibration of the oil pump on my M99 using the steps outlined in the owner manual. What I need to know is when properly calibrated, at WOT, is the pump operating at its maximal output or could it deliver more. If that was the case, it might be possible to ramp the pump actuating cable guide on the twist grip housing so that you would get more mileage on the pump cable vs. the throttle cable as you roll on the gas. Hmm... I also learned that after he freshened up the top end, the motor was making just over 160 PSI but with what I'm sure is the heat generated, I wouldn't be surprised if detonation was occurring. The issue with his bike is maybe an extreme application of the "dual purpose" concept since the bike is tasked with both highway cruising and trail riding. I'd be concerned that if he knocked a tooth or three off of the drive sprocket, the bike would be unsatisfactory for rail riding. Maybe not though. That's a good thought. I'm all ears if you have a combustion chamber mod that might help. Thanks Jack!

[matt glascock]

Hi Captain, another good point. I know he rebuilt the motor last spring where temps and humidity are in the 60's. I also know that he did check oil level at each fill for a down and dirty confirmation that the bike was oiling. The melt down was on a high 40's day (fact) with humidity in the 50's (reasonable guess) so no significantly different atmospheric conditions. I will give the check valve a thorough examination and report. I know the bike was performing well and then BOOM! I also know that this valve is going on my list of routine maintenance items to be checked. In a sense, the valve is a bit of an Achilles heel if the passage so small that complete obstruction could occur with minimal insult. Do you know if there is an in-line filter like we use on fuel lines with a porosity capable of transmitting oil? That might be a good addition. Thank you, Captain!

[Bullfrog]

It finally dawned on me that I haven't spoken plainly enough yet. I am very seriously concerned that all this discussion about lubrication is quite likely a distraction from finding what really caused the engine failure. And now we find that compression immediately following rebuild was 160psi (upper limit for running with pump gas - and before the rings seated). Add that to the description of the piston top and aluminum speckled spark plug - and seems clear that lack of lubrication did not kill the engine -- detonation did it. If the factors which caused the detonation aren't corrected, the engine will self-destruct again.
Ed

[matt glascock]

Yikes Captain, the plot thickens. I'm going to pass this information on forthwith! Is it possible that one begat the other ie lack of proper lubrication resulted in overheating leading to detonation resulting in catastrophic failure? Also, is it possible that something could have altered the ignition timing resulting in an advanced state. I didn't ask Jay if there was any pinging before meltdown, but will do so. I'm wondering also if it is possible he filled up with regular 87 octane gas. My understanding is that this would be a cause of detonation in an engine running higher compression under heavy loading. Man, there is a lot going on here. The engine is going to be completely rebuilt as soon as we get a hold of a new jug. After this discussion, I'm sure timing and compression will receive an extra measure of attention. Thank you, Captain! And thanks to all for weighing in on this issue. Much appreciated!!

[viclioce]

One thing is for certain Matt. This could easily demonstrate that the cost of using non-ethanol premium is far less expensive than the cost of a complete top end rebuild over the course of the short amount of miles involved! If this were indeed the case, be sure to drive this point home with your friend! Merry Christmas! Victor

[Bullfrog]

Ah, good. The plain talk appears to have opened consideration of the concept that simply changing to pre-mix might not solve the problem - I don't think it will.

Yes, many things COULD have contributed to the detonation . . . and reduced lubrication COULD have been one of 'em . . . but the description of the failed components doesn't match well with that.

We may never KNOW what truly caused the failure, and as is often the case - multiple things all pushing in the same direction may have "pushed it over the edge". Any of the following things could have caused the problem all by itself (and if any two or more combined . . .)
- excessive compression
- advanced timing (use of piston position indicator whether it is dial indicator or degree wheel is nice . . . but the timing light shows where it is REALLY firing)
- (who knows?) the dreaded "broken blue points wire" fault could be there
- potential of lean jetting (adjusted to be CLEAN at 60 degrees, then ridden HARD at 40 degrees)
- air leak could have developed over time since rebuild
- possible use of lower octane gas on the final ride
- . . .
- (and somewhere down the list) possible lubrication supply failure
Ed

[Hydraulic Jack]

The list of damages inside the engine speak more to detonation and piston meltdown than to oil failure. See prior comments.

The chances of hearing pinging in a two stroke at full throttle are about nil. A catastrophic detonation event, start to finish, may be only five or six seconds. Not much warning there.

Modifications to the cylinder head run from easy to exotic. Singh grooves, or as Racerclam calls them, Torque Grooves, are simply radial grooves cut in the cylinder head squish band, which cause turbulence and reduce tendency to detonate. Exotic would be a complete reshape using a toroidal profile. In the first case, compression will be reduced slightly due to having removed a small amount of material from the head. In the second case, you would be free to compute whatever head volume you want, controlling compression ratio. However, doing something like this requires not only excellent welding skills, but a milling machine and lots of research.

Usually, if point ignition changes, it retards, not the other way around, so I doubt that was the issue. A broken wire would be simple enough to spot. Just chase down the wire.

Pump gas is hit or miss. We simply trust that what it says on the pump is what we get in the tank. Only race gas these days uses only one octane rating method. Pump gas is based on the average of two methods. As long as the average is what it says it is, the actual component octane values could and likely do vary. Day to day usage, it matters little. Besides, modern cars frequently have knock sensors that will cause computers to alter timing to match the fuel, so they get by with iffy gasoline. Vintage two stroke engines, not so much. The better approach with a vintage engine is to tune for lower grade gas and play safe. This means lowering compression and retarding timing a bit.

I suppose you could run 20:1 every day, but it would be smokey, and I am not sure it is really needed unless the engine in question is really screaming. If the gearing is stock, how fast is the bike going at full throttle? There is no advantage to lugging an engine, as this can cause seizures about as readily as screaming it. Since the rider here is 200 pounds, changing gearing is probably not called for.

I would continue to verify oil delivery function, just to check off that box, but I think what happened here is a fuel related issue, not the lube oil. Not that the fuel was bad or wrong, but that the totality of facts left the engine susceptible at that moment to detonation. You can tune to exact factory specs, but it isn't easy to find 1974 gasoline.