Please, splain cam timing to me.

Discussion in 'Whizzer Motorized Bicycles' started by august, May 6, 2009.

  1. august

    august Member

    My motor is a new NE-R. Cam is one tooth advanced.

    I think I have blowback through the carbueretor, as the carb throat and air cleaner always have some raw gas laying in them after running, and it kind of sounds like air is being pushed backwards through the carb when running.

    I took the head off and watched the timing of the valves and piston when rotating the engine by hand and noting the position of the piston and valves during the four strokes.

    On the power stroke,the ex valve starts to open when the piston still has about a 1/4 inch of travel before bdc.

    On the exhaust stroke, the int valve is opening when the piston still has a 1/4 inch of travel before tdc. I think this is where I am getting some blow back through the carb.

    On the intake stroke,the piston goes down about 3/4 of an inch before the ex valve closes.The int valve is open from the top of the intake stroke until the piston is at bdc and then still open until the piston is 1/2 inch into the compression stroke.

    On the compression stroke, the piston goes up 1/2 inch before the int valve closes completely closed. I think I am getting some carb blowback on this stroke also.

    I tried the cam at the dot to dot alignment position, and it lessens the amount of time the valve stay open during opposing strokes, so there is less time that compression and power strokes are losing pressure through valve being open too early or late.

    I know there has to be some time for air to change directions and all that, but does this sound like maybe the cam is advanced too far?

    The engine does run with the cam one tooth advanced, but doesn't start as easily as I think it should, and I was only able to get 50 lbs on the compression tester.I had the head changed under warranty, as it was leaking,so I don't think head leaking is the problem.

    Would like to hear some ideas as to whether this amount of piston valve overlap is right, or should I put the cam back to dot to dot.

    Hope my description is not too confusing. I did compare my cam timing with the article that Quenton put into the Whizzer news letter, but couldn't come up with the settings that he described.

    Any help is appreciated Thanks August
    Last edited: May 6, 2009

  2. bill green

    bill green Member

    Hi sound more like you have valve leaking....Bill
  3. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi August,

    Do you have one of the cylinders with the oval shaped valve seat module? If so, all that I have worked on leaked real bad. The plate is usually installed at an angle and is known to move around because it is attached with 2 small screws [engineering that just amazes me]. Another problem with this system concerns the gasket under the block [did I mention the engineering just amazes me], and when it leaks it allows the exhaust & intake port to connect to each other. Please note in the attachements the loose fit and the serious mis-alignment.

    Best fix it to replace with an earlier 2005/2006 cylinder & head.

    Have fun,

    Attached Files:

  4. duivendyk

    duivendyk Guest

    Why did you play around with the valve timing in the first place?Increased overlap can improve performance at high speed,but reduces compression at low speed.That's why variable timing of he intake is common these days in car engines.These piston measurements mean little because they depend on the the stroke of the engine,they have to be related to crank angles.The only time both valves are open is at TDC at the start of the intake stroke when the intake opens before the exhaust closes.Typically the intake opens at about 10 degrees BTDC and the Exhaust closed 10 degrees ATDC.If the camshaft is rotated the valve overlap does NOT change,but ALL the valve timing is phased differently with respect to the crank,which looks like something to avoid.If you know the #of teeth on the camshaft gear,then the change in timing is 720/n,for instance with 36 teeth on the camshaft gear you're dealing with 20 !!!! degrees change,which is a lot.
    Last edited by a moderator: May 6, 2009
  5. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi duivendyk,

    It is important to tell you the Whizzer camshaft was designed to run one tooth advanced. The only reason it was retarded in the first place was to pass EPA requirements. So one tooth advanced is normal, and dot to dot is one tooth retarded.
    The difference between dot to dot and advance one tooth is 14 [13.84] degrees.

    The original factory settings on the WC-1 standard camshaft is I.O 24 degrees BTDC, I.C. 48 degrees ABDC, E.O. 32 degrees BBDC, and E.C. 31 degrees ATDC. The intake duration is 252 degrees, and the exhaust duration is 243 degrees.

    There are several versions of the hi lift camshaft and unlike the vintage camshaft it is just pressed onto the gear [no key, slot, or any other centering system] and often there is a difference between camshafts. That is why I always degree the camshaft I sold and sent information in package.

    A few [not many] were made with less than a stellar "press fit" and slipped. On the versions that were likely to spin the gear I always welded the gear in place.

    The numbers I wrote about in the Whizzer newsletter were the best settings and were arrived at with the intake valve clearance set at .006" and the exhaust set at .008". I have a special setup to degree the camshaft and if anyone wants to know the numbers on their camshaft, just send it to me and I will chart it out for free.

    Hope this helps,
  6. duivendyk

    duivendyk Guest

    I see,now it makes more sense,pretty wild timing 55 degrees overlap,thanks.
  7. WZ507

    WZ507 Member

    Piston position vs crank position


    Taking the cam timing numbers you provided literally, it sounds like your cam is timed perfectly. You said...

    On the compression stroke, the piston goes up 1/2 inch before the int valve closes completely closed. I think I am getting some carb blowback on this stroke also.

    The Whizzer engine has a 2.125" stroke and a rod/stroke ratio ~ 1.82, and using these dimensions you can calculate the crank position from the piston position, which in your case corresponds to an IN closing of ~65 deg ADBC, which is perfect timing for this mild short duration cam. The other opening and closing numbers are irrelevant since they are all fixed by the cam design. Bottom line is that from your numbers the cam is timed correctly and is not the source of your problem. As per Bill and Quenton's recommendation I'd be looking at the condition of the valves and seats. Let us know how you make out. Hope that splained everything to your satisfaction
    Last edited by a moderator: Dec 15, 2015
  8. august

    august Member

    Thanks all for the input.

    Quenton, I don't have the type of valve setup you describe, I have enclosed a picture of my cylinder.

    I sent the motor into Whizzer USA because of the head leaking. When I took the head off the first time , I don't remember what the valves looked like, I don't think I paid attention, because I was not aware of the different valve arrangements.

    When I got the motor back a couple of days ago, I took the head off because I was curious to check the valve openings, and wanted to see the condition of the head.

    One thing makes me wonder if this is the original cylinder, or if it has been swapped with one of the older ones. Some of the bolt holes have been fitted with heli-coils, doesn't seem like the new cylinder would have them since it would be brand new.

    I haven't talked to Dave at Whizzer yet, to see just what all they did to correct the leaking head.

    Any way this is what it looks like. I did pour some lacquer thinner into the valve ports to check for leakage, and they do leak some, but not real bad, just a drop every few seconds. The valves both have a clean looking contact area where they contact the cylinder, no visible areas of non contact, so I don't think I am losing too much compression thru the valves.

    What do you think about the cylinder, new or old??

    Thanks guys for the information I appreciate it!!!

  9. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi August,

    Looks like one of the cylinders I sent back because of striped threads. I used heli-coils to repair the threads, but it didn't work. The heal-coils also pulled the brittle threads out. It looks like Whizzer USA replaced your cylinder with an older version, however I am not sure the exchange was to your advantage considering both versions have problems.
    The valves should not leak any period!
    I would suggest you use valve grinding compound and lap the valves in, but considering the possible metal and head bolt problems I don't know if it would be a waste of time on your part.

    Manybe you should consider exchanging the cylinder again for one that hasn't been repaired. After looking at your pictures it appears the threads are in poor condition in several of the head bolt holes.

    Have fun,
  10. august

    august Member

    Thanks Quenton.

    I went ahead and put heli-coils in all the holes. I will torque them to the proper amount and see if they hold.

    I am in the process of lapping the valves, they are pretty close to sealing up tight, just need a little more time on them.

    I guess I would rather have this cylinder if it works as opposed to having the one with the modular valves. Doesn't look like there is a fix if the modular set up leaks.

    Thanks again August
  11. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi August, Just a thought.

    What if you were to paint the cylinder black [use hi temp cylinder paint], place the cylinder in a pre heated oven at 325/350 degrees for 2 hours [you know to bake the paint on], turn off oven let everything cool normally to room temp.

    Wonder if it will help? Sure won't hurt. Sometimes it works.

    Have fun,
  12. august

    august Member

    Worth a try. Thanks Quenton.
  13. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi August,

    I need to give you a little more information. I remove the valves, springs,"C" clips, and washers from the cylinder before "baking" the cylinder. The reason I do this is because I don't want the heads of the valves applying pressure against anything touching the aluminum.

    On the late 2007 and 2008 cylinders I had problems with the threads becoming brittle, not soft, and the threads would shear. Usually when the threads are soft they strip or round off and some threads will stick to the bolt. In this case the entire set of threads pull out of the cylinder, and leaves a hole that looks like it was made with a reamer. When I tried to fix the threads by using HeliCoils it failed to work and the HeliCoils started to pull out. After I thought about it a while it occured to me that the HeliCoils were also dependent on threads.

    When I discovered this problem I contacted Whizzer and eventually returned all of the cylinders and installed the rare early NE cylinder and the problems went away.

    Although many times the heat treatment works, it seems to work better on new cylinders as opposed to cylinders with longer run times.

    Have fun,