Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties to baffle or not to baffle, that is the question

to baffle or not to baffle, that is the question

Moderators: Curt!, Pa

Posts: 216
Location: Georgia
I have heard some discussion of the pros and cons of taking the baffle out of the case for the cylinder. I have heard it was originally designed to keep excess oil off the cyl. wall and with modern piston rings it should be cut out so more oil could get to the cyl walls. I have also heard that the vacume from the piston going up in the cyl. draws oil mist up on the cyl wall and helps to keep it cooled and lubed. I do not have the time or expertise to do fancy things like piston oilers or sporster oil pumps but thanks to Vtwin supplying the wrong rods my cases are split again. Now would be the best time to take the baffle out. Any thoughts?

Post Mon Apr 30, 2007 9:17 pm

Posts: 975
Location: Markt Einersheim, Germany

Not an answer to your question, but where in Georgia ya from?

I was born at Ft. MacPearson, and lived mostly in Smyrna/Marietta

Now in Germany


Post Tue May 01, 2007 6:49 am

Posts: 636
Location: Wisconsin, USA
The baffles don't work. Later u models had less baffling. I think that modern rings will eliminate the problem of oil getting to the combustion chamber. I am thinking of cutting grooves in the scrapers to allow for more oil splash from flywheels to cylinder walls. There is probably a happy place (exactly the right width and depth of groove) where you would gain oil splash to the cylinder walls without accumulating too much oil in the crankcase at cruising speed

Post Tue May 01, 2007 8:14 am

thanks to Vtwin supplying the wrong rods my cases are split again


Post Tue May 01, 2007 8:21 am

Posts: 3011
Location: Central Illinois, USA
I leave baffles in place for the simple reason that they stiffen the cases.


Post Tue May 01, 2007 1:40 pm

Posts: 801
Location: Planet Earth
There is more involved than just baffles and scrapers. There are a lot of UL's running around with and without baffles and no additional lubrication method provided.

Some are using 3 piece oil rings (rails and expanders). Most 3 piece oil rings are to tight for the stock oil system and the UL cylinders. They can have as much as 18 to 20 Lbs of drag. In a lot of cases you have a motor that is bore as you go. The ring drag can be adjusted slightly, or rings with less drag can be purchased.

Cast oil rings are more forgiving but a lot of the import rings are not made well.

You will have to use your best judgment about removing the baffles.

I am testing a few things that will help that do not require a lot of fancy work. But do require machine work. All will have been bench and road tested when done. Testing so far has given very good results.

Wont be ready for a while.


Posts: 216
Location: Georgia
See my other post concerning assembled rods and flywheels. I got them from Vtwin about 2 years ago and just a few weeks ago got around to installing the pistons and discovered the rods were too short. WRONG RODS!!

Posts: 216
Location: Georgia
Ft. Mac huh. Ever make it to the Steak King (Pilgreens). I do miss that place. Stewart Avenue is now called Martin Luther King Drive. The last ABATE swap meet at Lakewood was last Nov. They are tearing all the buildings at the fairgrounds down to build condo's, now that is just a sin. I am about 30 miles southwest of Ft. Mac.

Posts: 49
fhsmith1 wrote:
I have heard it was originally designed to keep excess oil off the cyl. wall and with modern piston rings it should be cut out so more oil could get to the cyl walls.

fhsmith1 wrote:
I have also heard that the vacume from the piston going up in the cyl. draws oil mist up on the cyl wall and helps to keep it cooled and lubed.


Also, use the worst oil control rings you can find.


Post Thu May 10, 2007 7:09 am

Posts: 636
Location: Wisconsin, USA
I am curious about the origin/source of the oil mist and what force of nature would draw the mist to the cylinder walls from the rod slot in the baffles. If splash from the rods and flywheels is sufficient on later motors, why wouldn't it work on the old flats. Why won't the rings I install on my knuck pistons work equally well in the u motor, with the baffles removed and the post scavenger scrapers removed? I am not trying to be argumentative here, just looking for answers. If the scraper capacities were equal, why would the underhead valve motor suffer? Not enough oil to the crankcase?

Posts: 216
Location: Georgia
The source of the oil mist theory was right here some time ago. If anyone has ever had a timing plug out while the engine was running they know there is a lot of mist in the crankcase. The theory of the baffle helping the mist to be pulled up onto the bottom of the piston, had to be that that the baffle helps to create a vacume under the piston while it is moving upwards into the cylinder. I have heard for a long time that the side valve engine cylinders creates heat more or either do not disapate heat as well as the over head valve. I have no idea about the ring theory.

Post Thu May 10, 2007 10:37 pm

Posts: 630
Location: belgium
Not trying to be smart but "typing" out loud :
The OHV's have some oil cooling the top...
Maybe the baffles are just for guiding the oil to where it's most needed : the piston friction path in the cyl.
P.S. I think the biggest drawback off the sidevalves is the hunk off metal carrying the valves...deforming the cyls when hot and blocking air to cool that side...

Post Fri May 11, 2007 7:22 am

Posts: 636
Location: Wisconsin, USA
When timing a 53 and up pan or shovel without a clear plug or the rubber scraper, I get something like an oil shower. I guess maybe the defination of "mist" is what I'm confused about. It does help considerably to tilt the bike as far to the right as possible, so the flywheel is running in less oil. but these motors are dumping most of the upper end return oil right on top of the flywheel. Steph, I think you are on to something with your theory. U cylinders always show the greatest wear at the sides of the cylinder near the top. I always thought the cause of this to be lack of oil reaching that area. I hadn't considered distortion as a source of the problem. But wouldn't more oil to that area reduce the friction, that causes the heat distortion? I realise that exhaust gas exiting thru the cylinder casting contibutes heat. Yesterday afternoon I gave my Chief a good run in the 85 degree heat and felt the cylinder right after I shut it off, I couldn't feel any real difference in temp around the cylinder. Why wouldn't you want to throw as much oil as possible, short of creating a wet sump problem. In previous discussions the consensus was that the return pump should be capable of keeping up, the difficulty may be in getting oil from the crankcase to the pump. Back to the subject, I have yet to be convinced that the baffles were ever any good for these motors no matter what type of oil ring.

Post Fri May 11, 2007 11:54 am

Posts: 636
Location: Wisconsin, USA
After I posted this morning I went to the shop and pulled out some U motor cases for a look at scraper configuration. The first set of scrapers past the scavenge trough are angled to divert the oil to the outside of the cases. The second set is angled to channel oil to the baffle slot for the front cylinder. How much oil was there to remove from the wheels after passing the two previous scrapers? I believe that around 1940 the rear baffles were eliminated, but the scrapers were still there. Later motors have no scrapers at the rear cylinder opening. All this fooling around makes me think HD engineers were tring to solve oiling problems. They completely eliminated baffles on the knuck motors, why not the flats? I know this is kind of trivial, and has been hashed and rehashed, but I would love to look a customer in the eye and tell him I can fix his big flat so he can get 40,000 or more out of a top end.

Post Sat May 12, 2007 1:19 am

Posts: 630
Location: belgium
Kyle, indeed the second(rear)scraper directs oil to the exterior...but with a clear passage at the left side, the right side is less pronounced.
But after that ALL is directed to the middle by the third scraper.
My guess is : the rear cyl got the first splash(biggest?)after ±270° so there's a need to collect oil after ±45° to be splashed on the front cyl.

About the heat issue, the outside off the cyls will have ± the same heat, but the leftside has only ± 2" fins, the rightside has± 2" nearly solid with another± 2"fins.
It's the± 2" solid that keeps the heat(with the exhaust passing thru) and I see no easy way to get oil overthere.
I think we could go further on this to say that bigger isn't always better.
Maybe the famous 13 fin cyls where abandoned for this.
That's what I understood between the lines...
Anders cyls had wear problems...maybe also because off this?
But all this is just...typing out loud!

Post Sun May 27, 2007 9:49 am

Posts: 304
Location: oklahoma usa
Many years ago I ran a 37 UL motor (for about 3 years) that had the baffles removed.
It was like that when I got it and never caused any problems.

Posts: 216
Location: Georgia
It is funny what you think about on a long ride.
Your explanation of the undisipated exaust heat causing excess wear on the right side of the engine is probably correct. All the oil splashed or sprayed under the piston would not seem to do much good.
Here is something whacky but it might get some conversation.
The oil head BMW came to mind. It used engine oil as a coolant.
What would happen if the return oil from the sidevalve scavenge pump were to be pumped back through a passage drilled through the cylinders?
The passage would have to start in the rear of the rear cyl. and go in between the bore and ex. valve. The oil would have to exit through another hole (turning about 90deg.) coming out the rt. side of the cyl. between the intake and ex. valve. The hole would have to go in at about the 2nd fin from the top and go horizontally. The oil would need to go back into the ft. cyl. in a similar manner between the valves and out in the very front of the cyl. It could be routed through a cooler on the front of the bike and back to the oil tank. The scavange pump gears look big enough to pump oil that well.
I do not know how much cooling would be realized by this but it would be a stabilizing amount. Some one with a pair of junk ones would have to volenteer to cut some apart and see just how much room to drill there would be. Just from looking at the ones I have from FHP from the outside it looks enough room.
The first person who got the idea of adding another spark plug to a panhead or shovelhead would have had to do some of the same experimenting as would need to be done.
Now I am bracing for all the jeers and convarsation about what I am smoking down in Ga. Someone tell me why this would not work.

Post Mon Jun 11, 2007 11:01 pm

Posts: 530
Location: Ogden, Utah, USA
Tricky bit of drill work. I would guess you would end up with a few plugs to close the unwanted end of the passage. Would there be enough oil flow in volume to make a difference? If this could contribute to less deformation of the bore it might be worth the experimentation. Maybe a fitting and run from the supply side and drain into the case? An external oil line running into a Flatty Cyl would make a lot of folks scratch the old noggin. :)
Steve H

Post Tue Jun 12, 2007 6:52 am

Yes, it will probably reduce the local temperature a bit.
The return pump will not develop much pressure because the scavenge oil is aerated, which also reduces its ability to absorb heat from the cylinder.
Many more leak possibilities.
A hole area big enough to run all the return oil through it, or to do any good may not be possible.

Post Sat Jun 16, 2007 3:09 am
On the VLs there were full baffles on the front cylinder and half baffles at the rear. The theory was this produced more suction to pull up oil mist on the poorly lubricated front cylinder. The rear cylinder is OK because it gets splashed oil from the flywheels because they rotate clockwise when seen from the right side of the bike. At this time no oil control rings were fitted on the front cylinder, and maybe not the rear either.

Sounds good, so why does the DL/RL/WL have a different setup, and why are so many VLs still running with missing baffles? I used to repair broken baffles, but this is a difficult repair and the new ones could break. I now leave them as found, in other words don't repair broken ones, but also don't cut out existing baffles.

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