Comments on: Replace Yamaha 2 stroke crank seals

By: Mccullouch Steven

Mccullouch Steven — Mon, 02 Nov 2020 13:32:42 +0000

Very helpful
Thanks for taking the time
Steel McQueen

By: Leon R

Leon R — Sat, 07 Mar 2020 20:38:34 +0000

I am currently restoring a 1988 Yamaha 480 Phazer snowmobile. Both crank seals were destroyed. The lips with the spring that goes around the crank were both ripped off and the springs were just sitting there. For the life of me, I can’t imagine what would cause this. Also, as for the orientation debate, The 2 seals, mag and PTO sides, were both in “backwards”. Now I have another Phazer engine here and upon inspection, those seals are in the “correct” way. Sooo, now I’m confused on which way to install the new ones. I kinda like the idea of the double lip design but have no clue where to look for those. Any help would be appreciated.

By: Chnjsgd

Chnjsgd — Thu, 23 Jan 2020 02:13:02 +0000

I have a CT1 and while try to get it to start after kicking it 30 + times with no luck , I was standing there and noticed oil dripping from the left( ignition) side case. What’s up, is that mean I need to replace the crank seal???

By: David DeMarest

David DeMarest — Tue, 07 Jan 2020 19:43:13 +0000

Very fine well written tech article. Makes for a good read for the “newbie” or done it a million times folks. Also, refreshing to see a polite exchange of knowledge.

Fasternu0

By: kevin

kevin — Thu, 28 Nov 2019 07:22:15 +0000

i am doing a 74 dt 250A right now and am putting the newer type crank seals i got from bike buzzerd
there good seals left hand seal 62xod 30id 10w
double lip. right hand side 62od 40id 8w just was going
to say the cuped side goes toward bearings and i smear
a very light coat of black ultra rtv around seal as i have always done. never had a problem i also put a notch with dimond bur on outer cup that butts up against bearing and i line up with lube holes that funnel down on bearings this alows better lubrication to the bearings and yes change the o-ring 93210-24235 the 73 and 74 share the same seal 75 and up take a diffrent seal that is still avaluable for sale at patzilla hope this helps sombody building one of these fine machines

By: Stew Naylor

Stew Naylor — Mon, 24 Jun 2019 04:07:45 +0000

1974 DT250A, did a rebulid last year, took me a whhile to get information on the correct orientation of the crank seals, as someone mentioned here the mag side seal in the photos is the wrong way around, the raised edges face the main bearing on the mag side and clutch side, there is also an “O” ring behind the gear on the clutch side that gets compressed to stop gearbox oil travelling along the shaft and gasses escaping. Incidently i didn’t renew that “O” ring and the crank case has filled with oil while standing for a few months. “DOH”
Good feed back and information on here so thanks folks

By: KEN ADAMS

KEN ADAMS — Thu, 02 May 2019 15:15:46 +0000

FYI I am talking about those tabs on the seal shown in your picture with the drywall screws in the seal , looks like they might correlate with the voids between the ball bearings inside the case

By: KEN ADAMS

KEN ADAMS — Thu, 02 May 2019 15:11:26 +0000

I have a 1974 dt 250 , bought it in 1978 . Just used your guidance here to install clutch side crank seal . All went well except after I put it in I realized I had not tried to line up the spaced hard rubber tabs on the inner side of seal with the bearings that were visible inside the motor . Will it make a difference or did I goof up . This article did not mention that .

By: anthony

anthony — Sat, 15 Sep 2018 06:33:02 +0000

Hi I have a 1976 YZ 80 Yamaha

Replaced the double sided crank seal twice.

Seal rides on a good collar.

Bike still blows a ton of smoke and transmission oil is still coming out the exhaust,

Washed exhaust, out of old oil as well.

Is it possible that the transmission oil is entering

the engine crankcase from between the crankcases

interface?

Crank bearings don’t wobble either.

And bike runs real good with a good solid idle.

Cheers.

crankcase

By: James mcnamara

James mcnamara — Mon, 16 Jul 2018 21:09:14 +0000

Hey guys I own a 1973 Yamaha ct3 that needs new seals. Having trouble finding them where I live in montana. If anyone has any leads or insight that would be super appreciated as so far all I’m finding is that they’re discontinued. Thanks in advance

By: matto

matto — Wed, 02 May 2018 22:24:48 +0000

Quick question is the 19mm nut regular or reverse threads? left/right? I need to pick one of those magneto pullers up.
Thanks, Nice write up, thanks for taking the time to put it together..

By: Ross B.

Ross B. — Sun, 13 Aug 2017 23:48:22 +0000

Interesting. I raced IT’s in the 80’s successfully in enduro events and even Trask. Worked on them a lot. Full tear downs to simple maintenance. Basically bullet proof. Even the smaller ones in the wide open Oregon desert event. But at my age I find it’s nice to reinforce my thinking on how to do things. Wish I could find all my old tools I made specifically for them. Great site.

By: Ryan

Ryan — Wed, 19 Jul 2017 19:53:21 +0000

Just saying, since the bottom end sees negative and positive pressure during a cycle, it doesn’t really matter with regard to seal orientation. Negative pressure when drawing in charge (most critical if you ask me) and positive pressure when forcing the charge into the cylinder from the bottom end. SO, in my opinion, dude/OP installed them the right way if you’re gonna tout the whole pressure to force the seal against the shaft. The intake into the bottom end (negative pressure) is what’s gonna throw off the mixture, so… not sure where the disagreement is.

If you wanna be super thorough, don’t get OEM single lipped seals. Get double lipped seals from a bearing/seal distributor – then it doesn’t matter which direction you install them if you’re worried about seal orientation and pressures. Often times domestic Viton is available instead of standard/import Nitrile which is what you’ll get from Fleabay. Do you really want “OEM” rubber in your bike anyway? I know I want the freshest rubber I can get regardless of where it comes from.

Lastly, DON’T USE RTV ON SEALS!!! Drive them in dry with a lubricated lip and make sure your sealing shaft isn’t damaged/pitted. If it is, you can let the seal sit further out if the assembly allows for it to ride on an un-corroded portion of the crank. Remove them however you want so long as you don’t contaminate your bottom end.

I’m not an old timer, but I know a thing or two, and this is how I do it.

By: Kevin B

Kevin B — Mon, 10 Jul 2017 22:40:37 +0000

This did help allot, I come back to it to the site many times to familiarize myself with what forgot.
Thanks

By: John B

John B — Sun, 09 Jul 2017 03:28:20 +0000

Great write up! Exactly what I’ve been trying to solve on my 79 yz400 resto.. Would lean out and run high rpm erratically, and motor oil was in crankshaft well. 2 crank seals and a countrrshaft seal going in next week.. Thank You!

JB, Phoenix, AZ

By: Carl Lavine

Carl Lavine — Sat, 17 Jun 2017 19:35:08 +0000

1978 dt175 new piston stock, new liner, crank seals new,vent tube to crankcase free, reed valves and assembly new, new carbarator,exhaust system removed and cleaned with heat.
These are the things we have done and still will not run over 5000rpm ,no idle with air filter cover on. Take air filter cover off 6000 rpm but air is coming out of filter.
HELP phone # 937-232-0064
Carlblavine@aol.com

By: Justin

Justin — Thu, 25 May 2017 22:32:36 +0000

Which way do i install the clutch side crank seal? I have the same seal shown in your pictures, the one side has a gold ring and the other is black with numbers. Do i install the seal wit the gold ring facing the crankshaft or the other way around number side facing the crankshaft?

By: Travis

Travis — Tue, 07 Mar 2017 13:39:28 +0000

Nice right up Ed. I work on a lot of 2 strokes. Cranks seals are very important, if you cannot get to idle or run smooth after a good carb cleaning more than likely the seal. I always put a thin film of yamabond or rightstuff on outer part of seals. This helps to lubricate seal so it does not chafe outer rubber on seals! I then wipe down outside of seal excess sealer after installed. Silicone should not be on inside of seal because it is wiping off excess as you are pushing into case. Larger 2 strokes you have to split cases because of a rubber rib to keep them from pushing out(street bikes and snowmobiles). This requires splitting cases. Reassembly requires yamabond or rightstuff. But with any motor very thin film of sealer is the key. Always when tearing apart take note of the way parts were removed and reassemble. If something does not seem correct google. Most crank seals are double lip seals, if they are smooth on one side smooth side will face outside of motor. Best way to find air leak is block off all ports and leak down check with 5 psig. I love bringing old 2 strokes back to life, happy wrenching!

By: Marcus

Marcus — Fri, 27 Jan 2017 19:49:25 +0000

Do you need to replace the gasket seals as well? Or can I reuse them to get to the crank seals?

By: Sammy

Sammy — Tue, 06 Dec 2016 05:29:01 +0000

I just got a dual shock Yamaha 80 the cylinder says 79cc how do I figure out if its a 2 or 4 stroke? Thanks in advance.