Looks like it is my labyrinth seal

[RDDave]

 
I have posted on this journey for quite some time now and I would like to again say, THANK YOU to all that have offered advice and encouragement.

I finally found an old retired Yamaha mechanic that would take a look at my 350. He rode the bike and double checked the adjustments. The bike didn't run right but all the adjustments were good.

After checking the usual adjustments, he did a simple test: He disconnected a spark plug, started the bike and raised the carb slide on the cylinder that he had disconnected the plug. The engine revved up. That was his test for the labyrinth seal.

I wished I had known of that simple test a year or so ago. Since I had checked, changed, swapped, bypassed, measured, double checked and checked again everything I could possibly think of.

So, I guess the engine has to come apart. I would like some guidance on how to approach changing the seal. I think I can get the crank out. I haven't done this kind of thing in decades and that was on single cylinder Enduros but I plan to try to split the RD's cases.

Who do I send the crank to? I can't change it myself, can I? I have other engines, but I don't know what condition the bottom ends are in and this is the original engine for this bike and everything works good if I can just get the engine to run right.

Thoughts, opinions, and suggestions would be appreciated.

.

[bitzz]

To replace the lab seal you have to break the crank down... you'll need a press. I think the hardest part of that will be finding a replacement seal.
If you have an "original", never serviced RD350 crank, it's time to do something with the crank. Bearings DO NOT last 50 years, even in a box on the shelf.

[busa1300]

Send it here https://www.billbune.com/

[m in sc]

what intakes are on the bike?  does it have a crossover tube? pic would help

[RDnuTZ]

I don't know what kind of pricing you are getting/expecting for a rebuild, but brand-new cranks are very reasonable. Last year I bought a VITO's modern updated crank off eBay and they are still selling there now for $479.00 and there is a limited time coupon for $20.00 off right now. Free shipping & no core exchange. Uses KOYO mains + Silver caged Upper & lower rod bearings.

I also bought 2 from HPR on eBay and they are currently $399.00 and they also have a $20.00 off coupon. They charge $32.00 for shipping. No core exchange either. Mains are TPI (Taiwan) and also uses the Silver caged upper & lower rod bearings.

Have not run mine yet but quality is top notch and lots of positive reviews on eBay.

[m in sc]

they come from the same factory i was told.

that being said, agree, i run a few vitos cranks. just replace it. however i am really dubious on that test. the only way a labyrinth seal will fail is of the inner main bearings failed, badly. if that happened, they would have to be so far out of whack it would sound like a concrete mixer running.

Keep in mind, i have rebuilt my own cranks numerous times in various bikes. i've -never-  had to replace a ( edit) labyrinth seal.


I don't know this guy, but just because somebody did something for a long time, doesn't mean they were particularly good at it. Just take it with a grain of salt. 

[KANDY]

++ to m in sc

[RDDave]

I am very open to any and all suggestions.

The intakes are stock and there is no cross over.

What else should I be looking for on this? Both he and I have checked, adjusted, rechecked and readjusted everything we can think of. Rodney was a Yamaha mechanic for decades. Has rebuilt dozens and dozens over the years. Doesn't make him perfect, but he absolutely knows his stuff.

Again, I am open to thoughts and suggestions.

.

[m in sc]

i find it hard to believe, but we learn every day. Me, id get a new crank and dump it in. after parts and labor, its not worth the aggravation of rebuilding a stocker. Like said, i can rebuild my own and its just not worth it anymore.   

If that truly is it, then we learned something new. a new crank is a good preventative if nothing else 

 

[RDDave]

If it comes to that, YES it will be a new crank.

Rodney is looking for his pressure testing pieces. He hasn't used them in years.

I'll keep posting as this moves along. After a couple of years, I am not getting in a hurry.

.

[m in sc]

if the seals have never been replaced, the crank needs out come out anyway, just to change the outer ones.

[1976RD400C]

From your previous post, is the problem that the left plug keeps fouling? Is that the only problem?

[RDDave]

It doesn't seem to be fouling nearly as much as it was. The Iridium plugs seemed to help a lot. But now the right cylinder is a bit weak. Comp is good on both; 100 or so. The big problem now is that the bike just doesn't run as good as it should SOMETIMES. And sometimes it runs good. It always starts good; two or no more than three kicks cold and first kick hot. And I can't find anything that changes. It is the most aggravating thing I have ever encountered.

I went ahead and changed the left crank seal just because it wasn't difficult and I was just not wanting to leave any stone unturned.

I also have a '73 250 Enduro that had running problems when I got it. I found it's issue straight away (the lobe for the points was dry and pitted causing the points to wear very quickly) and now it is a joy to ride. Starts and runs good and the same every time I throw a leg over it.

Rodney is going to try and find his testing equipment to test the lab seal before we do anything major. Meanwhile, we will test ride it and continue to check and recheck everything we can think of.

.

[RDnuTZ]

"SOMETIMES" sounds intermittent? If it was lab seal, wouldn't you expect it to be all the time?

[m in sc]

it absolutely would be every time. also a pressure test wont tell you anything on a lab seal. its not sealing unless the motor is actually running, and over 1000 rpm.

sounds electrical to me