Lower crank pressure question...

[skiracer]

Okay, I need a lesson in motor theory 101....  What causes excessive lower crank pressure; enough to push out the crank seal on the mag side.  The motor on my 250 has now done it twice.  This last time I ran the bike less than 6 hours.  The bike ran great, never missing a beat. Any thought?

1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer

[Oldebonz]

Usually a good thing for starting...warpage on case where seal seats??Lubing seal outer surface when installing? Freeze seal,use hot air gun on case where seal fits ,press in place with fingers.No lube on seating surface.

[KJDonovan]

James,

Pull the pipe off the bike and burn it out with an acetylene torch.  I am guessing you have some kind of guests that moved into the pipe or some other exhaust obstruction.  I did the same on Husky WR430 last spring and the problem was rodents in the pipe!

Thanks,

Kevin

[firstturn]

Oldebonz has great points and just to be sure measure you new seal (OD) and measure the crankcase(ID).  Had this happen three times by a competent Tech back in the 1970s and it turned out to be the wrong seal.

Ron Carbaugh

[Kip Kern]

As a rule, I use steel cased CR seals in the crank area not rubber.  My reasoning is the above problem plus rubber does not press straight.  I go old fashioned CR brand and arbor press them with a little Gasgacinch as lube/glue.

[skiracer]

Where do you get them?

quote:Originally posted by kip kern

As a rule, I use steel cased CR seals in the crank area not rubber.  My reasoning is the above problem plus rubber does not press straight.  I go old fashioned CR brand and arbor press them with a little Gasgacinch as lube/glue.

1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer

[skiracer]

I too have had this happen to me with a 175 Husky pipe.  I know this pipe is clear, thanks for the input Kevin.

quote:Originally posted by KJDonovan

James,

Pull the pipe off the bike and burn it out with an acetylene torch.  I am guessing you have some kind of guests that moved into the pipe or some other exhaust obstruction.  I did the same on Husky WR430 last spring and the problem was rodents in the pipe!

Thanks,

Kevin

1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer

[skiracer]

Thanks!  Very good points...

quote:Originally posted by Oldebonz

Usually a good thing for starting...warpage on case where seal seats??Lubing seal outer surface when installing? Freeze seal,use hot air gun on case where seal fits ,press in place with fingers.No lube on seating surface.

1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer

[skiracer]

Okay, some more details to what happened....  Upon removing the backing plate for the mag, pieces of the seal were hanging on the crank shaft.  When I removed the plate that holds the seal, the back half of the seal was still set in place within the plate.  So basically the front half the seal tore away from the back half. Or, to put it another way, the rubber seal portion ripped away from the steel casing of the seal......







1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer

[skiracer]

I posted a photo on the POG Facebook page for you to see.

1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer

[Kip Kern]

I get mine from Applied Industrial, (CR Seals)

[skiracer]

Thanks Kip!

quote]Originally posted by kip kern

I get mine from Applied Industrial, (CR Seals)
[/quote]

1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer

[Daniel P. McEntee]

I have been reading this thread with an interest in learning something out of it. In thinking about what you are experiencing, I thought about something a friend of mine told me years ago. He cautioned against using any kind of starting fluid to start a balky engine with, because it is much more explosive than a gas/oil mixture and you could literally blow out the main seals. This leads me to ask if you have had any problems starting the bike and done this, or have any problems with it backfiring really bad? Using really high octane fuel or some kind of exotic race gas? If the pipe is nice and tight, and you have a big backfire, the resulting pressure has to go somewhere and maybe the seals are a week point, especially when you think about the condition you found them in. Maybe some sort of timing issue? Just my uneducated wild a$$$@# guess.
    Type at you later,
     Dan McEntee

[skiracer]

Dan, thanks for your interest and input. You have given great questions and observations. Okay, no back firing, no special gas just non ethonal. Bike starts on the second or third kick so no additives there.  I checked to see if there was play in the crank bearing; none felt. If a crank bearing starts to go bad wouldn't I feel a lot of vibration from it? As far as the timing and compression I take a concerative stance.

1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer

[454MRW]

I don't have access to a 76 MC5 250 timing information, but the 74 manual shows 2.55mm BTC, and the 79 shows 2.0-2.1mm BTC. If you're within those specs I would look for a restriction in the pipe possibly from carbon build up or debris from mice moving around while running. If you're not experiencing any spark knocks I would assume your deck height is okay. You might try using red Loctite threadlocker if the seals seem a little loose. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1978-1979 MX-6 175 & 250 KTM's
1976-78 125-400 RM's & 79 PE250 Suzuki & 2012 DR650
2007 CR125R Honda
1977 MC250 Maico