'84 Honda NN50MD (Gyro) Oil leaks into crank

[mini_man]

I'm new to your forum. Glad to see there is an army of folks keeping these old scooters alive!

I've owned my Gryo for the past 15 years. I've always suspected that the there is an issue with the auto injector oil system, because when the bike sits for extended periods, starting is difficult, having to you starting fluid, and when it does get running, it smoked heavily for a few miles. My suspicion was that oil was leaking past the oil pump, down the manifold, into the crank.

I just finished doing a ring job on her, and I had it disassembled for 3-4 weeks, awaiting parts. When I got into reassembly, I did see a bunch of the oil laying in the bottom of the crank case.

Being that the pump is NLA, and it has $100+ price tag, I'm inclined to live with it, but it does bug me.

Has anybody out there have any thoughts or experience with this? There is a lot of similarity between the Gyro and Aero 50 scooter.

Thanks!

[zuphilius]

Welcome to the forums! A few of us here have gyros, but very few. I have had no experience with this but I have a couple thoughts on the matter. My thoughts are I hope it doesn't happen to my Gyro!! I just ordered a petcock so it will be on the road soon.

Someone here will have valuable input soon.

[mousewheels]

Hi,
The Gyro oil pump sometimes fails that way. I've received a couple bad ones on used Gyros. Zuphilius - I don't think it's a fate for all. If you have no problems now, that's a great sign. I've seen Gyro's over 10k with good oil pumps.

As far as substitution goes - I've never tried. Check things out carefully if going that route. The Aero/Elite SE/88-93 Elite SA50 have a different orientation for the oil cable. Shaft I think is different plus the Gyro has an extra gear reduction between the crankshaft and oil pump drive shaft. Make sure the swap delivers the proper oil ratio.



-- Pic below shows my latest Gyro's bad oil pump. Time to accumulate that puddle was less than 1 week.

[mini_man]

That looks like an S model. Looked up the fiche, same pn...


How long did that take to accumulate?

Do you have any spares to offer? Any suggestions of a source?

THanks

[mousewheels]

Correct - its a TG50, Glad you looked up the compatibility, I've swapped pumps between the NN50 and TG50, but didn't remember if they were exactly the same. That oil pump leaks a lot, it took less than a week.

--
I don't have good oil pumps around, but they show up on eBay fairly regularly. In fact there are 2 NN50 pumps there now. Item 400060970770 (49.95 BIN/Free shipping), Item 280508220728 (34.99 BIN, shipping calculator to your zip). I have no association nor have bought parts from those sellers.

Will take the bad one in the photo apart this weekend, post pics & compare with a Spree pump.

[mini_man]

I seen those listed, that you mentioned.

It's hard to get excited about some of these guys on ebay, who are posting junk at high prices.

I'm going to do you little test, so I can quantify the leak. At least I would have a base line for future comparison.

Have you dissected any of those faulty pumps, to gain insight on what is the issue with these pumps?

Thanks for you insight!

[mousewheels]

I didn't tear down the Gyro oil pump this weekend - got a test to try out first.

Photo below is a Spree type oil pump which I took apart a while back. There's an explanation at the thread http://www.hondaspree.net/phpBB3/viewto ... 39&p=63940.




There is a check valve on the oil pump output. It is lightly sprung to resist the normal flow. I think it's set to be closed against static oil pressure of the tank, preventing oil from flowing past the shaft/oil pump housing clearances and into the crankcase.

Gyro_Oil_Pump_CheckValve.JPG (19.13 KiB) Viewed 12430 times

Plan is to swap the check valve from a Spree pump, and run a static oil leak test for a couple days.

[maddog]

look for an o- ring on the shaft, normal life span for these pumps are 50,000 mi.

[mousewheels]

look for an o- ring on the shaft, normal life span for these pumps are 50,000 mi.

Thanks maddog, 50k miles is a lot of scooting .

I have looked into the shaft seal, it is a spring loaded lip seal like a crank seal. The photos show a Spree pump, but a Gyro is very similar. One thing to note, is the factory assembly process was to press in the seal, put a washer over the top, then swage the case to retain the washer and seal. The photos show the pump after grinding down and removing the retaining washer. To duplicate the OEM assembly, after replacing the seal, we need to come up with the means to positively retain the seal.


Backside of the seal identifies dimensions. 9.5mm Id, 16mm Od, 4mm thick. Took rough measurements to verify numbers.


A couple sources for the seal were found a while back:-

http://www.mfgsupply.com/m/c/501415.html$3.99 + 6.99 ship
http://www.gokartsrus.com/80049-oil-sea ... -2157.html$2.85 + $15? min shipping/handing



-- Gyro's are built such that a leak at the shaft seal goes into the transmission oil --
When a guy with a Gyro says his crankcase is full of oil, or it smokes when starting after sitting a while, the oil pump shaft seal is never the problem. The oil pump shaft is *outside* of the crankcase. If the oil pump leaks at worst it will fill up the gear case with GN2, then overflow out the breather tube for the crankcase. In the photo, the breather tube is just to the left of the oil pump.



-- Comparison photos for Gyro vs Aero and Spree oil pumps --
The Gyro pump seems to be unique among US Honda scooters of the era. Mounting and the orientation of the oil metering shaft are unique. The Spree pump casting is the most similar, except for the mounting (not visible in the photo) and lack of a variable control for oil output. Both photos show the difference in shaft length and gearing.

Gyro_vs_AF05_oil_pumps.JPG (27.42 KiB) Viewed 12391 times

Photo below shows Gyro vs Spree. Also it shows the Gyro pump after swapping in the Spree pump output check valve. Testing will start this weekend to verify if the check valve will show a difference on the leaking Gyro pump.

Gyro_vs_Spree_oil_pump.JPG (18 KiB) Viewed 12393 times

Update: 08/22/2011 - Gee, I forgot about getting back with the results of testing. Replacement of the check valve cured the oil leakage problem. After a typical 8 month mouse hibernation, the spring startup was successful. Oil pump problem solved for this one's failure!

[mousewheels]

Update - I sectioned a check valve to support construction info earlier in the thread.

Oil_Pump_Check_Valve_sm.jpg (49.78 KiB) Viewed 11555 times

Oil_Pump_Check_Valve_2_sm.jpg (47.24 KiB) Viewed 11555 times

Valve seat close up. It may not be cause of failure, but I note all surfaces exposed to oil are rough. The portion of the valve seat and body which was press fit remains much smoother and shiny. I suspect the entire valve seat was once smoother.

Oil_Pump_Check_Valve_Seat.JPG (94.23 KiB) Viewed 11555 times

Edit 11/21 - new pic. Shows ball contact as shiny patches

Oil_Pump_Check_Valve_Seat_2.JPG (95.25 KiB) Viewed 11483 times

[swflcarl]

Mouse... you are definitely one of my favorite folks here. You are well researched and very thorough - plus your supporting attachments are always helpful. I have had run into two failed pump (failing open) - which I bought cheap replacement pumps from folks here.

My beloved gyro is still fine... but it is awesome that you drove down to the failure item (check valve seat) in the pump and came up with a feasible work around.

Much kudos to you...

[ClemSpree]

+1 mouse, thanks for chopping one up. After seeing the section I think I'll try to "unpress" fit the seat/base from the top with a tiny punch and some heat. You've convinced me that it is a ball and spring(it should be) despite what I heard during the air test.

I think the spring is likely typically fine, debris or wear on the seat is probably the culprit. If I can get mine apart, I'll try to use some valve lapping compound on the seat and ball.

BTW, I found on the net that maximum male human exhale is around 148cm water and a vigorous exhale did not open mine so the spring should be plenty strong, it only has to hold back about 25 cm of head pressure.

I'll post any findings in this thread vs my other one to keep the pump/check valve stuff together.

[mousewheels]

Thanks guys
> I have had run into two failed pump (failing open) - which I bought cheap replacement pumps from folks here.
Glad you found reasonably priced (and non-leaking) replacements!

>I think the spring is likely typically fine, debris or wear on the seat is probably the culprit. If I can get mine apart, I'll try to use some valve lapping compound on the seat and ball.
+1 -- Since you have cleaned the valve, I'd recommend whatever tubing kudge is needed to get the valve only directly on the line to the tank for a drip test. Wish I'd tested mine before tearing it down. *Years* ago I cleaned it and was about to re-install, but went with the Spree valve swap for it's own sake.

> I'll post any findings in this thread vs my other one to keep the pump/check valve stuff together.
Ok - here's a link to your thread:
[url-http://www.hondaspree.net/phpBB3/viewto ... =3&t=28647]Link to ClemSpree's thread on working to restore a bad check valve[/url]

[ClemSpree]

First of all, kudos to mouse for his photography skills, this stuff is tiny.

The check valve is fairly easy to disassemble, use a small punch or a flattened off finishing nail to go through the outlet and drive the ball and base out. I drilled a blind hole in a piece of wood so that I could have a firm base to strike against and so the spring and base would be captured.

The spring is very light, mine measured 1/2" as found, I stretched it to about 5/8".

The ball is easy to lose(3 times-found it 2X), disassembling a grease fitting yields a ball that seems to be of the correct size(you're welcome:). You are not likely to be able to easily polish the ball or seat everything is very small. My seat looked similar to the pic, its finished but not polished.

It just so happens that the check valve fits perfectly in the supply line from the oil tank(86 Spree) so its easy to do a leak test.

So far, no leaks, I'll probably do the same to the other but it doesn't leak quite as bad.

This, or something like this may be an easy solution:
http://www.usplastic.com/catalog/item.a ... &catid=489

I'd probably disassemble and remove the innards of the OEM check valve if I was adding another just so the flow isn't reduced too much.

As a footnote, an Aero125 fitting is a 90 degree and looks to be slightly bigger, I didn't check any other scoots, there's an Aero motor sitting bare here so that one was easy.

[mousewheels]

Good work

I'll take the next bad check valve apart and follow.

>> disassembling a grease fitting yields a ball that seems to be of the correct size
that's a fun find.