Blowby Article

[CBAS5]

Yeah, I've seen those run-ins during the factory tours. Not much load on the motor and they don't run them very long. They're not hurting them.

So that would imply that load and duration of running are related to microwelding. What exactly do you mean by not appling too much load. Here's how I understand load. Higher gears = more load on engine. Higher rpm = more load. More throttle = more load. Should I guess they're light with the throttle and rpms? Also, does that mean no passengers during breakin? Would passengers cause unnecessary load?

Btw, here's something I found on blowby posted by you awhile ago. It discusses the same things you discussed here, but it goes a little more in dept. I figured somebody may be interested.

HD's have a variable volume crankcase due to the 45 degree common crankpin arrangement. Since the pistons are only 45 crankshaft degrees apart, they arrive at BDC 45 degrees apart and again at TDC 45 degrees apart. So the volume of the crankcase is constantly changing.

The problem this causes is that the motor tries to inhale when the pistons go up and then exhale when the pistons go down. If it's allowed to inhale, you end up with a lot of air moving in and out of the motor. When this happens, it tends to pick up oil inside the motor and deposit it outside the motor.

So to keep this from happening, HD fits the breather vents (or vent in this case) with a check valve. The motor can exhale, but not inhale. In the absence of any blow-by getting past the rings, the crankcase alternates from atmospheric (pistons down) to a vacuum (pistons up). But in the real world, a little gets past the rings, so there's a net outflow equal to that.

So if the check valve isn't functioning properly, it'll cause this issue. Likewise if the motor has excessive blowby (poor ring seal) it'll cause it.

A leak down test is the best way to check ring seal. The tester is not expensive and it's handy as hell. Listen for where the air is coming out during the test: intake port, exhaust port, or breathers. To test the check valve, take that hose (it leads up to your air cleaner), and see if you can blow into it. It shouldn't let you.

There's another possibility, too, and that's wet sumping, i.e. the oil pump isn't removing the oil as fast as it's feeding it. If the cam box fills with oil, it comes out that hose and right to your air cleaner. It's been a chronic issue on XL's for years, happens on the 5-speed bikes as well as the 4-speeds and the ironheads, but often on the head breather models you never know like you do on bikes like yours with the breather on the cam box. They love to pump oil up that hose when it happens.

The oil pump was updated in '98 and you rarely see this anymore, but we still see it on high rpm race motors from time to time. It's always the best sealed motors that have the issue, especially gapless ring motors. Vacuum in the crankcase interferes big time with scavenging.

The 98-up style pump can be fitted to the older bikes, hell I've put'em on ironheads, that'd be something you could try. It's a nice upgrade regardless. Beyond that about all you can do is lower the oil pressure. But don't go down that path unless you establish for sure that's what's happening.

[JeffEdmo]

Originally Posted by aswracing

A better test would be a leak down test. A leak down test is the best way to check the mechanical integrity of the motor without tearing it down.

Is it necessary/possible to perform leak down tests at various stages of the compression stroke? What I mean is, when you pressurize the cylinder the piston will move to bdc, correct? This will only allow you to check blow by at the end of the stroke. Are you able to hold the piston at differing points in the cylinder to check blow by throughout the stroke?

[JeffEdmo]

Originally Posted by aswracing

Anyone who does that mototune crap on one of our engine kits can just forget about his warranty. It's a recipe for ring microwelding.

Would you mind describing in detail your opinion for the proper break-in procedure for a fresh engine? Fresh meaning just put back together from having cylinders bored, new pistons & rings and head work.

[SierraBiker]

Originally Posted by JeffEdmo

Would you mind describing in detail your opinion for the proper break-in procedure for a fresh engine? Fresh meaning just put back together from having cylinders bored, new pistons & rings and head work.

Jeff
I think this is what you're looking for

Originally Posted by aswracing

The first run-ins are the most important. We like to start the motor and run it for about a minute, with fans blowing on it. Then let it cool ALL the way down. Repeat but the second time run it 2 minutes. Next time 3 minutes, etc. The idea is to let the rings do their job without overheating. They're very sensitive to localized overheating when only a little bit of them is touching the cylinder wall and you can damage the pistons easily.

[stevo]

I'll back what Aaron has said with my own experiance as an engine builder for many years...(this doesn't mean I've done 2 883-1200 conversions...but rather working as an engine/reconditioner/builder for many years on car, bike, truck, marine and earthmoving motors.)

The longer I'm in this game and the more I learn...the less I know....


I didn't know much about micro-welding untill about 5 years ago...... although I used to run all my engines in stages to "seat" everything and allow them to take the high spots off everything without getting too hot and find their "happy" place (funny, I just re-read the Axtell article mentioned by Aaron and Ron refers the surfaces being "happy" together... so I'm not the only one )..

I use a very similar technique to what Aaron described and that's running the motor for small periods, progressively longer each time and allowing time to cool completely between runs.....

After it's done 1/2 a dozen cycles or so I'll take it for a short run and then let it cool....

I add a step that some others don't use... I've found this seems to work for me and I've never had oil issues with a motor that I've done this to.....
To my knowledge I havn't had micro weld issues with this technique but the motor has been heat cycled quite a few times BEFORE I do this

I'll do this again a little longer and then I take it to about 80kph in top and crack the throttle untill it gets to about 110kph and back it off fully....

This pushes the rings into the bore and the backing off allows oil to be drawn up which cools the ring off and removes the metal you've just scraped off the bore....I cruise for a while and repeat this step a few times...


If it's one of my engines I'll sometimes be very gently and may take a few days to get the initial ring bedding done......I've also run a motor in on the drag strip to try the "Mototune" method and it was down on power compared to what I had in the previous and later setup...


There is also a lot more parts in an engine than just rings and pistons


Here's a copy of the S&S running procedure which is a damn sight better IMO than the Mototune crap



Remember engines are like women...... if ya want a happy one ya gotta run it in right .. and if it's not happy then your life is gonna be miserable



How should I break-in my new S & S engine?
NOTE - S & S Engines require premium gasoline (octane 91 or higher) for best performance. Octane boosting gasoline additives may be necessary with marginal gasoline.

CAUTION - Low octane gasoline and hot weather can cause detonation and extensive engine damage. Never try to power through ignition knock ("ping," "rattle," etc.) by opening throttle.

CAUTION - If engine is run with foreign material in
the oil tank, engine damage will occur. Engine
damage caused by foreign material in the oil tank
is not covered under the S&S warranty.Clean oil tank and oil cooler and flush or
replace oil lines before installing engine in
frame.

Engine Break-In Procedure
Note: S&S engines are designed for high performance
and as such are not as tolerant of inadequate break-in
as stock or lower performance engines. Correct breakin
will assure longer engine life and will prevent
unnecessary engine damage. Engine damage caused
by improper break-in is not covered under the S&S
warranty.

A. Initial start up. Run engine approximately one
minute at 1250-1750 rpm. DO NOT crack
throttle or subject to any loads during this period
as head gaskets are susceptible to failure at
this time. During this time, check to see that oil
pressure is normal, that oil is returning the oil
tank, and that no leaks exist.

B. Shut off engine and thoroughly check for any
leaks or other problems. Let engine cool to the
touch.

C. After engine has cooled, start up again and
allow the motor to build some heat. Engine
should be run no longer than three to four
minutes. When the cylinders become warm/
hot to the touch (approximately 150) shut the
motor down and let it cool to room temp. Follow
the same cautions as for the initial start-up, and
continue to watch for problems.

D. Repeat this procedure 3 or 4 times. Each
successive time it should take slightly longer to
warm up and you can increase the temp slightly
each time (+10). You can be more liberal each
time with the rpm, gently vary rpm continuously
from idle up to 2500 rpm in the final cycle. Don?t
be too concerned with final carb settings at this
time because idle speed and mixture cannot
be correctly set until the motor reaches full
operating temperature. The motor should not
reach that temperature during these cycles. Do
not allow engine temperature to become
excessive. After the motor has cooled to room
temperature for the final time you are ready to
start the 1000 mile engine break-in process.

E. The first 50 miles are most critical for new rings
and piston break-in. Engine damage is most
likely to occur during this period. Keep heat
down by not exceeding 2500 rpm. Avoid lugging
the motor, riding in hot weather or in traffic. Vary
the engine speed. Do not lug the engine. We
recommend changing the oil at 50 miles.

F. The next 500 miles should be spent running
engine no faster than 3500 rpm or 60 mph.
Avoid continuous steady speeds, and do not
lug the engine. Vary engine rpm. We
recommend changing the oil again at 500 miles.
CAUTION - Lugging or running engine prematurely at
sustained high rpm may result in damage to pistons and
other engine components. S&S voids it's guarantee if
engine is not broken in properly.

G. For the balance of the first 1000 miles the motor can
be run in a normal but conservative manner. You can
be more liberal with the rpm range and motorcycle
can be operated at normal highway speeds. Avoid
overheating or putting any hard strain on the engine:
no drag racing, dyno runs, excessive speed, trailer
towing or sidecar operation.

H. After 1000 miles, verify carburetor jetting and
adjustment. Change the engine oil. Motorcycle can
now be operated normally.

I. Have Fun!

[supercharger]

There is a very real problem with the methods described by S&S and Stevo and Aaron.

We all don't build engines and bikes in shops where we have the wherewithal to do this labratory grade break-in.

Most of us pick our bike up at the dealer and RIDE IT HOME.

I kept it under 60 and varied my RPM's all the way. My only heat cycles were getting caught in the rain twice on the way home. Both times I found dry shelter (read gas station) and shut her down while I waited out the weather. My second wait was well over an hour until the downpour stopped and I still had to ride partway home in light rain. The engine cooled completely that time.

So much for the "labratory" break-in procedure. It sounds great, but it is in no way practical for most of us here.

My bike runs great too. No oil usage, no oil in the air cleaner, great gas mileage and a very good dyno run at 1300 miles.

[stevo]

but now ya know for when ya do a rebuild or go bigger.....


it depends on wether ya want OK ... or best possible

[cantolina]

I disagree.....I don't think its "laboratory" at all....and one could start this procedure on their way home from the dealer....

None of it is set in stone, mind you, except for certain restrictions that make sense...

I broke in my last conversion much like this....The engine was never a problem...ever...

Hell, I wish I had that power train back, to be honest.....

[DV8]

This is a great thread. Some of the most detailed reasons for blow-by I have seen. Thanks for all the info.

I have been geting a lot of oil out of my case breather, and this explains it. What kind of check valve can I run if my sporty is vented out of the case and not the heads?

[bunny32]

Originally Posted by DV8

This is a great thread. Some of the most detailed reasons for blow-by I have seen. Thanks for all the info.

I have been geting a lot of oil out of my case breather, and this explains it. What kind of check valve can I run if my sporty is vented out of the case and not the heads?

The valves that work best on crankcase breathers have several features:-
1/ Low-inertia, i.e. they don't take more than a breath to open and close.
2/ They operate at low pressures ~1-30psi
3/ They preferably have a floating type seal.
4/ They should be transparent, so you can see if they block up with blowby, solids, bugs etc.
5 They should be easy to open and clean occasionally
6/ They should push-fit into your breather line.

Metal diaphragm valves with e.g. springs are hopeless. Avoid car PCV valves as they are metering as well as non-return valves and are unsuitable. Also avoid other types of valves designed to work at high pressures e.g. plumbing valves.