Motor Air Leak

[VICTOR MONZ]

I intend to ride my Six Day on Sunday at Glen Helen and know about lap (3) it will begin to overrev.  It is my opinion, it has an air leak where one material expands at a different rate of thermal expansion than another when she warms up, my question is what is the best and simplest way to locate the leak to solve the problem.

It has a "D" cylinder with the rubber manifold and a 28 Bing.  I have sealed it with all types of "goop" and added a fork seal that snaps on the manifold, spaced out properly between the manifold and the face of the intake.

If there is another potential location, I could use the advice.

It can catch me off guard and miss a turn or worse yet not healthy for the motor, sooner or later.

Any assistance would be greatly appreciated.

Victor

[Bob Marsh]

crank seal?? magneto side

[slvrbrdfxr]

Victor,
I'd say the best way to find the air leak is to pressurize the top end. I had  a similar problem awhile back and built an inexpensive tester from some common items purchased at Lowes and Auto Zone. I then used a hand bicycle pump to supply the air. You only have to pressurize the top end to 6 psi and then start spraying with soap solution until you see bubbles. I located the leak in about 5 minutes and it turned out to be the magneto side seal even though the engine bottom end was a fresh rebuild including a brand new seal. I have pictures of the tester I built and will send them to you if needed. You can email me by using my screen name here followed by @cox.net.
Dave McCullough

[tomale]

Yep. thats the way to do it... good idea to have a kit to check for air leaks anyway... I have seen cylinder that leaked not around any seals or gaskets but actually in the casting itself... These are old bikes after all.

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)74'
250 hare scrambler (project bike)

[Randy Kirkbride]

Hi Victor,
I had the same problem on my 'D' cyl 6 Days. I also tried to seal the intake manifold with everything. It did not look bad, but when I replaced it with a new one, the problem went away.

[joe novak]

Victor,   I checked my records this morning, and your "D" Sachs cylinder is being recalled for faulty air leaks, and misplaced power band.  Please package the cylinder, head, and 28mm Bing carb, and send it to me ASAP.  Upon my receiving the "D" cylinder, head, and carb, I will send you a "standard replacement" (ie 1972-1973) cylinder (55.5+ bore), head, and 27mm Bing (choke included).  Thank you for your continued support and enjoyment of Penton Sportcycles!   Joe Novak

[VICTOR MONZ]

Randy.

Where can I get a new manifold ?

That is where I believe the air leak is....your assistance would be greatly apprciated.

Victor

[sixdazed]

Victor,Sudco may have a Mikuni manifold that will work-i think they have a chart with measurements in their catalogue/website.If you want to borrow a pressure tester i can send you one.Also i've been sore/tired since Laughlin and haven't looked yet for the other item you need;)-i'll check tonite and see if i have it and a spare D manifold.Later,Ric

ric emmal

[Randy Kirkbride]

Victor,
I used a Mikuni manifold on mine. You'll have to match up the measurements on their chart like Ric suggested. I had to cut the mounting holes into slots to get the bolts to line up. I'll see if I can get you more info (model #).

[VICTOR MONZ]

Looking forward to your replies....wishing for the correct unit and not Mikuni....but like Dad said wish in one hand and ....well you guys know the rest.

Will search the POG Site....I think we covered this before and someone posted the Mikuni chart.

I'll let you know what I come up with ...

Joe...what's your address...I'll get the shipment ready for you....just wait by the front door !

Victor

[sixdazed]

Victor,No luck yet but i have a bunch more cylinders to check and possibly teardown some assembled engines if needed.Hang in there.
Do you want to borrow my pressure tester?                                                       Ric

ric emmal

[joe novak]

I agree with Dave, Thom, and the others who responded.  First check the top end for air leaks, then the bottom end, cases, gaskets, seals.  If you have a Bing 28, I think the cap has two screws which attach it to the body.   Be sure the seal is intact (O-ring).  I had a Big carb which would get dirty in the air screw area which would cause a lean mixture.   Good luck finding the leak, and let us know what you find.   Joe

[gooddirt]

I would go for the the mag seal. If the carb manifold is leaking it would do it right away; as there is not much heat around it. What kind of fork seal is there and is it rubber to rubber? put a very thin O- Ring to take up the void; should be 1 to 2mm at the most.(sachs badges)------Ric if you find a extra -D- carb manifold I could use one. Thanks LG

[VICTOR MONZ]

Did I hear Sachs Badges ?  

The seals have been replaced within the last 10 hrs or so....guess it wouldn't be too hard to just do it and kind of a differntial diagnosis process.

Thanks for all the input.....still want to replace the manifold if one becomes available.

Victor

[john durrill]

Victor,
 Here are the manifolds Mikuni offers for motorcycles.
One of them would probably work if you elongate the holes. Can you post the measurement between the stud holes and the id where the carb is clamped and the id where the manifold mates to the cylinder for us?




 Mikuni does make a few other manifolds like this for snow mobiles.
john d.