Fulton cams

[Dewey]

Hi all -
I have the honor of restoring the Fulton Douglas engine. I'm new to Douglas but motorcycles and engines have always been my passion. I've taken a lot of pics through the teardown process and wanted to share some of my findings with other Douglas enthusiasts. The first 2 pics are of the cams that came out of this engine. Note that they are very different from each other. The intake looks fairly normal while the exhaust is quite aggressive. I did a quick mock up of the engine (not perfect but reasonably close) to get an idea as to the valve events more for documentation than anything else. My desire is to find an exhaust cam of the same profile as the intake. I may have to have the existing exhaust cam built up and ground back down to meet these specs if a direct replacement can't be found. Just one of many issues within the engine.

My findings were intake opens 30deg., closes 52, lift .303", duration 262, centerline 101deg.
                       exhaust opens 60deg., closes 30, lift .301", duration 270, centerline 103deg.
                                                                      (cam wear)
                      LCA = 103deg.

Pretty radical for a touring flattie.

[Doug]

Dewey,

Yes the inlet and exhaust cams are distinctly different. Actually the exhaust cam is what you would typically expect to see with a roller tapper follower. The inlet is more typical with flat or large radius tappets.

Stock timing is:
Inlet opens 5 deg BTDC
Inlet closes 45 deg ABDC (230 deg duration)
Exhaust opens 60 deg BBDC
Exhaust closes 20 deg ATDC (260 deg duration)

Valve lift for both is 0.3125 inch

It looks like the intake cam is set advanced. Otherwise the cam durations are not that far off, other being a little longer than expected. This may be due to not allowing for valve clearance in the way you are measuring, and your readings are including a portion of the 15 deg of quieting ramps on either side of the flanks. The minimum clearance (cold) is 0.006 inch for both inlet and exhaust. So i do not think the cams require re-profiling.

-Doug

[Fix typo. 08Oct11 -Doug]

[Dewey]

Thanks for the input. I had taken into account .006" of travel before marking the opening & closing events and had also considered that the intake was 1 tooth advanced. 1 tooth represents 22.5 degrees at the crank making it open at 7.5deg. which is much closer to normal. My biggest goal was to figure out what the duration was to determine engine running characteristics. I would have to agree that the inlet cam does in fact look like one used with flat tappets. Didn't the Douglas go that route later on? If so, someone must have adapted one to fit or perhaps it fit without any changes. I'm not terribly concerned with the lift being short by .010".

I'm glad to hear that you feel the exhaust cams' profile is normal for this engine. The wear has gone through the hardface so I'll have to have it repaired which is not a problem. I can do that here. 

Dewey

BTW - it was late, I was tired. I mistakenly posted the exhaust centerline as 103deg. when it should have been 105deg.

[Doug]

Dewey,

Douglas did use flat tappets before and after the S6 models. The 350cc machines retained the flat tappets right through, and they went back to that much simpler cam arrangement on the big twins starting with the Blue Chief of 1935. The flat tappet style cams are not interchangeable nor would be easily modified to fit an S6 variant.

-Doug

[Dewey]

Thanks Doug. Having such knowledgeable folks as yourself in these forums is a huge asset to maintaining the marque. Any clue as to what the intake cam might belong to if in fact it might be used with something other than roller tappets?

Dewey

[Doug]

Dewey,

I think there is a misunderstanding. That is the correct inlet cam for the S6 type engines.

-Doug

[Dewey]

Doug -

Perfect! Thanks for clearing that up.

Dewey