Adjustable cam gear

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lmcchesney
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Adjustable cam gear

Post by lmcchesney » Sat Mar 20, 2004 2:16 pm

This is regarding my 96x78 rebuild project. We will be using adjusted 2.0L D-jet FI system and gave up trying to find the ultimate cam. I went with the Web Cam 73 grind and lifters. My mechanic, Denny @Autocraft Engines, said he cannot obtain the best cam advancement with the stock cam gear and suggests to go with an adjustable stright cut cam gear. The costs approx. $260.
Question:
1. When I use the timming on my simulator for a 73 grind I am using 0.05 lift and 224° duration and intake centerline of 103° and lobe center angle of 108° with +5° advance. Are these correct?

2. Are all adjustable cam gears stright cut?

3. Who is the best source to obtain the cam gear from?

4. If you use a stright cut cam gear, do you not need a stright cut crankshaft gear?

Thanks,

L. McChesney

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raygreenwood
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Post by raygreenwood » Sat Mar 20, 2004 3:32 pm

No, not all adjustable cam gears are straight cut. Yes, you must use a straight cut crank gear as well. From memory, the advertized cam specs seem right for a web 73. I would not use straight cut gears. They are noisey. They also wear faster. Also, the debris f rom the wear is steel. Be very careful of hwat you use...and that it has proper oil pump clearance, or that will be all she wrote. When you are done with all of this, you may needto slot the trigger plate in the side of the distributor to change the initial position of the injection triggers to have a smooth idle. Exactly how far is he trying to advance the cam? I would be careful here. watch your vacume signature. There is also no reason why the stock gear...and it should be a webcam stock gear for best results with that cam....cannot be machined, have the eccentric washers dropped in...and do exactly what you need. Might it just be easier to re-position the cam a notch or two over and make note of it...then re-position the distributor drive to match? I would be careful if you want to keep the D-jet. A lot can be done with it, but most in-experienced mechanics (in-experienced with D-jet I mean)....patently ignore the two facts that some semblence of close to factory vacuum signature must be upheld and that the FI is timed to the cam...and its timing is barely acceptable at low rpm the way it came. Just soem thougfhts. Ray

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lmcchesney
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Post by lmcchesney » Sun Mar 21, 2004 12:23 pm

Appreciate the information Ray.
I do not wish to use stright cut gears,(noise and less longevity). Others suggested to refit the standard Web Cam gear for adaquate timming. I believe my mechanic, Denny McNutt, is seeking about 5-8° advanced to improve low end torque.
I realize the injectors are timed off the cam via the injector triggers, but I thought the injector triggers were advanced/retared by adjusting the distributor as in ignition timming.
Could you expound further on that adjustment by slotting the trigger plate?
Agree, we have to assure clearence of the cam gear bolts from the oil pump. It may require grinding the bolt heads.
Thanks,
L. McChesney

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Dave_Darling
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Post by Dave_Darling » Sun Mar 21, 2004 12:29 pm

The injection timing will be changed when you rotate the distributor body. The trigger points, after all, are attached to the distributor body.

They are mounted to a curved plate that is held onto the side of the dizzy by two screws. Ray is talking about slotting the holes in that curved plate where the screws go, or at least ovaling them. That will let you rotate the trigger points one way or the other.

Ray and I have been around about this in the past, and the short version is that I am not as sure as he is that the exact injector timing is critical. Though I cannot argue with his results.

--DD

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raygreenwood
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Post by raygreenwood » Sun Mar 21, 2004 8:07 pm

Dave is correct in the fact that the injector timing is not really that critical (in stock tune) to overall running. You will generally not notice anything above 1500 rpm if the timing is out. But you will notice and idle lumpiness and generally a slightly richer smell at idle sometimes. The D-jets were generally tuned from the factory a hair bit richer than they needed to be, to allow the out of time cylinders to not be a real issue at all.
I do know from experience though, then when compression goes up, tuning gets tighter, and advance slightly higher than factory is used, the injection timing starts running into a bit of trouble. Nothing too serious...but it usually requires slightly richer mixture to make it idle right. That starts to upset the curves farther up the line in rpm. I found that slotting the plate holes allows keeping the correct or best operating trigger plate position the same, as cam or ignition timing is advanced. Just something to watch for. Ray

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Dave_Darling
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Post by Dave_Darling » Sun Mar 21, 2004 9:34 pm

OH! Thank you, Ray! Your note just made it "click" in my head. :idea: I think I had not understood what you meant in your earlier notes, but now it makes much more sense. I like it when the light bulb suddenly comes on... :)

--DD

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lmcchesney
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Post by lmcchesney » Mon Mar 22, 2004 8:33 am

Thanks Guys,
The injector contact plate seems to be attached to the distrubutor housing via cheese head screws. Do you need to convert to bolt/nut to make adjustable slot?
Specifically, what do you time the injector contacts to? (BTDC, TDC?)
Thanks,
L. McChesney

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Dave_Darling
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Post by Dave_Darling » Mon Mar 22, 2004 12:11 pm

Screws work just fine. All you do is oval the mounting holes.

You tune the trigger points for best idle, pretty much. If you've got dyno time, you also tune for best power.

--DD

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raygreenwood
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Post by raygreenwood » Mon Mar 22, 2004 4:59 pm

YES!...You are right on! Even if you are not making any real changes to the engine, its amazing what slotting the plate and carefully diialing the trigger point location can do....after you have set proper ignition timing. It can make a decent difference off the line on some engines. One peculiarity I have noticed. When the timing is set perfectly (ignition)...and you are moving the slotted plate (trigger), when you go too far in the other direction....either direction....you can see a huge difference to the pressure guage on the fuel pressure. I have not yet exactly figured out wether this is a timing upset issue in the ECU...or that the actual timing and resulting atomization change is affecting the running of the engine enough to disturb the vacume signature....casuing the MpS to make the fuel pressure fluctuations you see. Its something I'm working on, because the swing of the needle is radical. So is the resulting change in idle. Ray

Guest

Post by Guest » Tue Mar 23, 2004 11:19 am

If you use a Crane Optical Points system (3000 - 700) you can adjust the Optical points position and FI trigger point position independently over a wide range. No hole slotting is required.

Ken

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raygreenwood
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Post by raygreenwood » Tue Mar 23, 2004 1:18 pm

So in actuality, the optical pick-up is on a slotted...or somehow mobile mount so the distributor body movement is only tied to the trigger points...correct? Thats nice.

Part of some of the discussions I had a while back concerning sequential injection is tied to this. Just moving the triggers on these cars causes a large fluctuation in the off the line performance, the idle and teh stability of the fuel pressure. Wether that stability problem is caused by poor running augmenting the vacume signature ... actually casuing the ECU to lengthen the injection duration via the MPS....or if it is just causing poor running through very out of time atomization....is not fully clear yet. But the problem is significant. This is not to say that at some level the fuel pressure/volume response of the system cannot be tuned enough to make timing irrelevent. CIS does not time itself to teh valve openings...then again...they are always spraying. This is what Iwas getting at in past discussions. The timing does not appear very critical on D and L jet at all. But there will come a point...on non constant injection like this...where the injection point may become so far out of time that the spray of fuel gets totally brought to ground ...so to speak on the inside of the manifold. Of course, as the rpm picks up, this will be less of a problem. The time factor gets much shorter.

But, the ability to only inject what you need...having no wasted atomization...but having the intire still atomized injection be pulled in through the valve should have some benefeit in acccuracy at all levels. Hopefully I will be able to see this when I get my engine running in the late summer or early fall. Ray

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lmcchesney
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Post by lmcchesney » Mon Apr 05, 2004 11:29 am

Some threads relate to adjustable cam gear failure. Thus far, my understanding is the following regarding adjustable cam gears:
Stright cut adjustable gears can be made of steel or Al.
Stright cut adjustable gears produce a high pitched sound at higher RPM's.
Helical cut adjustable gears do not make the high pitched sound.
Helical cut adjustable gears are made of Al.
Al. gears have reports of breaking under load.
Steel gears do not seem to break.
Does anyone not agree?
Adjustable cam gear vs stock non adjustable cam gear:
56 teeth/360° gear = 6.4°/tooth.
Five bolt patern = 11.2 teeth per 72° sector.
Since you cannot have 11.2 teeth the teeth do not align on the same degree spot on each sector and thus each sector is 0.2 x 6.4° = 1.28° diffenerce in the teeth arranged on each sector.
Thus, to obtain 1.3° adjustments, you use different sectors to mount the cam gear.
Thoughts/Comments?
Thanks,
L. McChesney

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raygreenwood
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Post by raygreenwood » Mon Apr 05, 2004 11:43 pm

I may be mistaken, but I have never heard of anyones cam load breaking the aluminum gear. If there is that much pressure on the cam from the lifters and springs...or from difficulty in turning, there are other problems. The benefit from straight cam cam gears...supposedly...and I have no reason to doubt it....just the necessity for it, is that without the helix of the gear, there is little or not end thrust put on the cam or its bearings. Of course, you could simply put in double thrust cam bearings and usually have no worries.

The deeper gear penetration of the straight cut gear has more heel and toe wear, so requires a harder metal. The only benefit of the adjustable gear (yes more and finer teeth could be nice..but not really necessary)....is that the holes for the bolts are slotted. What is generally used, are flanged bushings that also serve as the washer under the bolts. They have eccentric holes drilled in them, that allow specific offsets when a different # bushing is installed. I thought that at one time, bug pack used to sell eccentric bushing kits for cams. Its not really difficult machine work. You may also check and see if Schrick or Neuspeed can help you find those. Though they are mainly water cooled....a bushing is a bushing. Ray

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lmcchesney
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Post by lmcchesney » Tue Apr 06, 2004 10:32 am

Thanks again Ray.
Information from Jake
Dial in cams became logic cam in the 90s..... They made the gears for MSHP.

I have seen so many sets of elliptical cam gears that I absolutely quit using them.

Alot of them are not round, and its hard to measure them to see if they are. The only way I have been able to do it is by putting a smal bit of lapping compound on them and running them together in my lapping fixture. Then take it apart and clean them up and start looking for consistency of the lapped areas.. If its not consistant, they are not round.

I have seen a single engine snap off three cams before the owner finally listened and threw his away.
Additionally, I really don't think I would tolerate that high pitch whine from the stright cut gear.
Chris just responded that the five mounting holes are not equally spaced.
L. McChesney

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