Need help understanding cam timing behavior

BigBobsL · Post by **BigBobsL** » Thu May 12, 2005 12:56 am

My "fully built" 5.4 lightning has a set of cams that I knew were not degreed and suspected were incorrectly grond since the Left bank had 165 psi cranking compression (+/-) 2-3 psi, while the Right bank had 125 spi, same +/- 2-3 psi. A check of leakdown showed 2-3% leakdown and truck made good power 470 rwhp on Mustang Dyno with 14# boost.

Finally found a set of adjustable cam gears. Found left (driver's side) cam Intake LCA at 120 and right cam at 114. LSA as "supposed to be 114 and installed at 110 LCA, 4 degrees advanced. After I corrected the cam timing the truck lost 60 rwhp and very noticable power at anything above 2500 rpm, but idle cleaned up a lot.

Checked compression and left bank now at 90 psi and right bank at 60psi! Checked leakdown again to make sure nothing hurt, still at 2-3%.

So assuming I had left the degree wheel slip or something, went back, found TDC again and and re-checked timing. Intake LCA was correct and as I left it. I have checked the LCA of the exhaust on the left bank and it 114 rather than the 118 I expected (is my math correct?). So it appears LSA on the left cam is 110 rather than 114. I have not checked the LSA of the right cam yet.

Cam design is supposed to be: 0.590" and 238 degrees @ 0.050" at intake and 0.600" and 242 degrees at 0.050" and 114 degree LSA.

What has me puzzled is decreased peformance and drastic compression drop. Should I go back with correctly ground replacement cam in retarded position or get a bigger cam. This is a daily driver that gets raced regularly and was making good power before "correcting" cam timing and is presently getting a bigger blower.

Thanks in advance for your help and wanting to get this right, these motors are not known for easy access.

ADR · Post by **ADR** » Thu May 12, 2005 2:20 am

Big Bob
Exactly how did you determine lobe C/L ??

The more you retard those cams the more compression will be lost.

You need solid lifters to check with and you have to use the ".050 up the ramp" method not the "drop down from the top method". Those cams are not symetrical.

Almost forgot....you can't have any backlash in the chain when checking the timing...this might take two peaple...one to turn the crank and one to make sure the cam chain stays tight. I do it by myself on an engine stand but when the motors in the truck it could be a two person job.
Dale

BigBobsL · Post by **BigBobsL** » Thu May 12, 2005 7:54 am

Dale, thanks for you help. I am using solid "lifters", but was determining LCA by measuring 0.050" drop from maximum lift.

Cam card states: "If using "Lobe Center" method of degreeing, cam should be installed on an intake centerline of 110 degrees." Assumed technique I was using was appropriate and that it would check since drop from max lift was so small. cam timing also check same at 0.100" drop.

Will check again using lift off heal of cam, thanks again.

Any ideas why compression would drop with cam advanced?

Bad95Gts · Post by **Bad95Gts** » Thu May 12, 2005 8:06 am

Exactly were and how are you indicating the cam?
Are you taking any steps to keep the slack out of the chains during indicating and are you only turning one direction?
Also have you tried checking centerline only going .010 off of peak lift.

BigBobsL · Post by **BigBobsL** » Thu May 12, 2005 9:19 pm

Turning cam only one direction. Checked with manufacturer and was advised that cam lobes are symmetrical. Chain tensioners are pumped up and no slack in chain.

Certain I will be replacing the cams since it appears LSA is off by four degrees on at least one cam and suspect the other is worse due that bank consistently having lower cranking compression. I do not understand why cranking compression dropped so dramatically by advancing cam.

ADR · Post by **ADR** » Thu May 12, 2005 9:24 pm

Big Bob
The compression should never drop when you advance the cam....
Dale

ADR · Post by **ADR** » Fri May 13, 2005 3:00 pm

One last comment for BigBob....when standing in front of the engine, you are spinning the engine "clockwise" to time the cams....right??
Dale

liteitup · Post by **liteitup** » Fri May 13, 2005 7:36 pm

probably the only question i will ever be qualified to answer on this board

, as i was the one doing the spinning
yes, clockwise

BigBobsL · Post by **BigBobsL** » Sat May 14, 2005 11:35 pm

Checked by 0.050 timing events, centerline and total duration of the drivers side (left) cam This technique gave the same result as previous check, 110 degrees, thus installed correctly. Have not checked the other side yet.

What is confusing is that I had recently advanced the left cam 10 degrees and the right cam 6 degrees to get them installed correctly. Gutted rattling cats at same time. Since then power has been down and compression appears low, but leakdowns are excellent. Keep coming back to why compression is low.

I will be buying another compression gage to confirm compression. Anything else besides cam timing that can reduce compression and not affect leakdown?

Gutted cats could have reduced effective collector length and be responsible for the power loss if compression proves OK

Racer7088 · Post by **Racer7088** » Sun May 15, 2005 1:37 am

Bob,

Your cams are simply in wrong unless you have some big EFI or tuning problems? What was the tq before and after you degreed these cams? Could a plug or injector or more not be firing? The fact that your compression DROPPED after advancing the cams means maybe you degreed in the cams off of the wrong lobes also possibly.

BigBobsL · Post by **BigBobsL** » Sun May 15, 2005 11:40 am

Racer7088 wrote:Bob,

Your cams are simply in wrong unless you have some big EFI or tuning problems? What was the tq before and after you degreed these cams? Could a plug or injector or more not be firing? The fact that your compression DROPPED after advancing the cams means maybe you degreed in the cams off of the wrong lobes also possibly.

Erik, Appreciate your help and you know the truck and myself, this is the white Lightning from HALO that made 470 hp on your Mustang dyno.

It might also help to acknowledge that this is not my first cam to degree. Although it is the first of two OHC mod motors I have degreed. The other is doing fine, this one is not. Trust me, I doubted myself and am still checking and re-checking timing. It was (and remains) the obvious first place to look and I am still double and triple checking it. If I do have it in incorrectly, that is an easier problem to fix. Problem is it still shows to be in correctly. I am degreeing cylinders #1 & #6 with #1 being front on passenger side and #6 being 2nd back on driver's side.

Thanks again - Bob

hotrod · Post by **hotrod** » Sun May 15, 2005 7:14 pm

Anything else besides cam timing that can reduce compression and not affect leakdown?

The only things I can think of are "build" related issues on the engine itself. Not sure if they apply to you, not knowing when / if the engine had major work done on it etc.

Have you checked to see if the installed heights of your valves are the same on both banks. I know of one person that for some unknown reason had slightly shorter valves on one side of an engine (different manufacture and a rebuilt engine).

On overhead cam engines block deck height can be critical to proper valve timing! If the cylinder head is slightly lower or higher than it should be the cam drive belt is in effect advanced or retarded on that cylinder head. I know of one person that had a subaru flat 4 engine decked and it totally screwed up his crank angle and cam angle sensor signals and the ECU just flat freaked out.

Not familiar with your engine, is it possible to put the cam gears on the wrong bank, ( ie left side cam gears on the right side cams ). If so and the cam gears are timed slightly different that could give you fits as well.

Also any chance your heads are different on the two banks, or deck height on the block is off on one side, or wrong head gasket, giving you different compression ratios on the two sides of the engine ??

Larry

let r eat · Post by **let r eat** » Sun May 15, 2005 10:29 pm

Have you verified true TDC??

BigBobsL · Post by **BigBobsL** » Fri May 20, 2005 2:00 am

Second call to cam manufacturer, this time told cams were indeed asymmetrical. Checking again with 0.050" events show cams retarded 4-6 degrees. Pass cam ground on 110 LSA and drive side at 114. Have sent the cams back for their confirmation, but tech rep said he would have to check with owner before replacing them because I have had them more than two years. They have only been in the motor for a year and 15,000 miles. To my thinking, no matter how long I have had them, if they are ground wrong they are ground wrong; time will not change that. If they do not replace them, next set will be purchased elsewhere.

Yes - good advise on keeping tension on chain when rotating the motor. Even with tensioner oil filled, I found some slack in tension side of chain occasionally due to valve spring kick (valve closing events).

ADR · Post by **ADR** » Fri May 20, 2005 10:34 pm

BigBob
Glad to see you got it in a direction....one more thing I might add is that when you put it back together...Ford has an updated cam chain tensioner that is a must have. Dont let the fact that it is made of plastic bother you, what you are really after is the ratchet delete. I suppose you could remove it from the cast iron ones but .... anyway its good to get rid of it, it will save your front cam bearings.
Dale