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Need advice 360 timing chain cam/crank slightly off

340challconvert

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Purchased a 360 from Mabco to put into my A66 340 Challenger short term while I pull the 340 for a rebuild.
I bought a hp version with flat top pistons and installed hp cam sited as a 272 cam
Cam specs; 272-272 duration 454 lift 110 lobe separation 52 degrees overlap, 216 216 duration @ .50
Power range 1500-5200 Considered the largest "stock" cam for this engine
In going over the engine for parts install; the timing marks are slightly off.
I call the manufacturer and he stated to leave the chain as is.

Pistons are flat top 30 over, no valve notches, piston to deck measurement is not a stock (deep in the hole) 360 with the higher compression pistons it measures out at about .087 below deck with number 1 piston at TDC.

I am no expert, and I have installed cams years back always aligning timing marks; is there a reason for the manufacturer to alter the timing in this manner with this hp cam and flat top piston? Looks to be one tooth off?
Pic of timing chain sprockets and Number 1 piston at TDC
Any thoughts appreciated.

IMG_8963.jpg


IMG_8964.jpg
 

Jm73340

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The only way to know if the cam is installed correctly is to use a degree wheel and degree the cam. Timing marks on the gears or sprockets can be off.
 

Challenger RTA

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Is that the position you installed the cam? did you rotate the crank after installed? If so just redo it. clay chamber for valve clearance. Did the cam come with an offset key?
 
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Bret Schneider

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Why do you believe there's a problem with the timing mark on the cam? Looks like you just have it a tooth off. Maybe I'm missing something here but not sure what the problem is.
 

Chryco Psycho

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I will second for the third time to degree it ,
it is advanced from the picture which can help bottom end power but I bet you are 12* off so it will not run well like that .
the cam specs seem pretty lame so you could install a far better cam , , it has low lift & a 110* lobe separation which is better with headers but no compression to boot , everything seems to be off using that cam .
 

340challconvert

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Is that the position you installed the cam? did you rotate the crank after installed? If so just redo it. clay chamber for valve clearance. Did the cam come with an offset key?
Engine came w cam and gearing installed as per the specs above. I did compare the cam sprocket/slot; same as stock sprocket. That is why I was wondering if they altered timing for the cam. I just went to TDC and timing dots were offset slightly.
 

340challconvert

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Agree. Degree the cam. Advancing the cam would help bottom end and retarding the cam would help top end.
Doing either one also affect valve to piston clearance.
Did you contact the camshaft manufacturer or the engine builder ?
Advancing / Retarding a Camshaft
I asked the manufacturer about the timing marks, they gave minimal info and said to not alter the sprockets to line up
 

340challconvert

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I will second for the third time to degree it ,
it is advanced from the picture which can help bottom end power but I bet you are 12* off so it will not run well like that .
the cam specs seem pretty lame so you could install a far better cam , , it has low lift & a 110* lobe separation which is better with headers but no compression to boot , everything seems to be off using that cam .
The cam was their upgrade with the higher compression pistons. I also have other new cams/lifters I could switch out. My main concern is; did they modify timing with the offset timing marks for this cam. I plan on also checking piston to valve clearance. I have aluminum Eddie’s designed for the above deck hi compression 340 I plan on using.
 

Chryco Psycho

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as I said 1 tooth off is about 12* it won't run well like that , the window is 4-5* either way
 

Steve340

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You really need to piston stop it too find true TDC. A nut and a piece of flat steel will do it.
There is a dwell period at TDC and BDC were the piston stays still but the crank can be a few degrees off TDC.
Best make sure it is not a tooth off while it is easy to rectify.
 

Challenger RTA

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IF you think something is wrong it just might be. I agree with Chryco Psycho as he said 1 tooth off is about 12* it won't run well like that , the window is 4-5* either way. Just because they been in business and are "professionals" Mabbco of TX? Things do go wrong!
BASIC WARRANTY-Subject to the limitations, restrictions, conditions and terms herein, Customer must provide written notice of any defect to MABBCO within 90 days from the date of sale or within 4,000 miles from same, whichever first occurs with respect to the following: any Basic Short Block or Basic Long Block furnished by MABBCO and installed in an automobile, minivan, SUV, pickup or other covered application; any Premium Long Block furnished by MABBCO installed in one of the following applications: ambulance, off-highway vehicle, package delivery vehicle, police vehicle, taxi, tow truck, fork lift, industrial application, marine engine, boat engine, logging truck, moving truck or van, or any vehicle equal to or over 3/4 ton.

Motor Assembly - Once the motor's components are cleaned, machined, and tested they are assembled by skilled and experienced engine builders, with access to computer data bases, to ensure the motor's components are properly built-in accordance with published specifications.

6 BEFORE ANY REPAIRS CAN BE MADE, A REPAIR AUTHORIZATION NUMBER MUST BE RECEIVED FROM MABBCO. DISASSEMBLY OR REASSEMBLY OF A MABBCO LONG OR SHORT BLOCK OR ANY COMPONENTS THEREOF WITHOUT AN AUTHORIZATION NUMBER RECEIVED FROM MABBCO VOIDS THIS LIMITED WARRANTY.
7 The Customer must notify MABBCO of any warranty claim prior to repair for assignment of an authorization number. The authorized work will be performed either at MABBCO’s factory in Tyler Texas or by another vendor approved in writing by MABBCO prior to the performance of any work. It is the sole responsibility of the Customer to pay for any non-MABBCO approved parts and labor, and in writing submit a claim with the alleged defective parts shipped prepaid to MABBCO for its review and sole determination of the claim’s validity.
 
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Challenger RTA

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By no means I am not an expert. Maybe They have a special grind cam,I don't think so.I’ve read about camshafts that some cam companies grind advance into the camshaft. How does the cam company grind advance into the cam?

Everyone tends to look at the intake and exhaust lobes as separate movements within the engine’s operation, but what we really need to do is look at the entire function of the camshaft and how all the different events coincide. It is true that many camshafts are designed with advance built into them. The majority of these cams are intended for street use. Here’s how it all comes together.


The cam companies know that when it comes to choosing a camshaft, many enthusiasts tend to suffer from the “More is Better” theory of engine performance. The common approach is that if some additional lift and duration is good, then more is better. So instead of choosing a typical 220 degrees at 0.050-inch tappet lift cam for a mild street engine, many enthusiasts – especially first-time buyers – will upgrade their selection and go with maybe a 236 or 242 degrees at 0.050 cam instead because a buddy told them that’s what they needed.


The unfortunate result is that these longer duration camshafts tend to reduce low-speed torque in favor of top-end power. The camshaft companies know this. One way to improve the low-speed torque on a camshaft with too much duration is to advance the intake lobe in relation to the exhaust. Advancing just the intake lobe opens and closes the intake valve sooner which is one way to help improve the low-speed torque.


We’ve included a Comp Cams illustration of the intake and exhaust lobe lift and duration curves on a simple diagram that makes all this a little easier to understand. If all the cam company did was advance the intake lobe position on the cam, this would also decrease the lobe separation angle and increase the number of degrees of overlap.


ask-11-01


You can learn quite a bit just by studying this Comp Cams illustration of cam timing. Advancing either lobe would move it to the left while retarding would move either lobe to the right on this diagram. So you can see how advancing just the intake lobe (the one on the right) would change the intake centerline but also increase overlap.


Overlap is the amount of time, in degrees, when both the exhaust and intake valves are open. You can see this represented by the small triangle shaped area in the center bottom of the two curves. Overlap was called the “Fifth Cycle” by Ed Iskenderian back in the 1960’s when engine builders were first discovering how much mid-range power can be improved by adding overlap. The downside to increasing overlap is that it tends to hurt idle vacuum. This is also what creates the classic lumpy, uneven idle that everybody wants so their engine sounds like a killer Pro Stock drag race powerplant.


Bu too much overlap can really hurt the off-idle performance so the cam companies typically advance the intake lobe and retard the exhaust lobe to maintain a decent lobe separation angle. For example, almost all Comp street cams use a 110-degree lobe separation angle.


There is a very easy way to tell if the camshaft has been advanced by the cam company when the cam was machined. Look at the cam timing card and compare the lobe separation angle (LSA) with the intake centerline number. If the numbers are the same, then the camshaft has not been advanced.


Let’s look at an example. This first example is a Comp cam we currently have in a 496 big block Chevy we built. It’s a mechanical roller with 261 degrees duration at 0.050-inch tappet lift on the intake and 270 degrees on the exhaust with 0.734-/0.737-inch valve lift (PN 11-851-9). The intake centerline is listed on the cam card at 108 degrees and the LSA is also 108 degrees. In this case, the cam has been ground with no advance as the numbers are the same.


Now let’s evaluate a much milder Comp hydraulic roller camshaft for an LS engine. This is PN 54-456-11 with 219 and 227 degrees of duration at 0.050-inch tappet lift with 0.607-/0.614-inch lift. When we look at the cam card, the intake centerline is listed at 107 degrees while the LSA is listed at 112 degrees. The numbers tell us the intake centerline has been advanced five degrees from 112 to 107 degrees after top dead center (ATDC).


As a simple exercise to put all this in perspective, there is an easy way to mathematically determine the lobe separation angle. This does not necessarily require measuring the camshaft’s intake and exhaust centerlines. But for right now, let’s say we have the numbers with the exhaust centerline at 112 degrees BTDC and the intake at 112 degrees ATDC. Simply add the two numbers together and divide by 2. The equation would be:


112 + 112 = 224 /2 = 112 degrees LSA.


In the case of the LS cam, we know the intake centerline is 107 degrees ATDC and the LSA is 112, so if the exhaust was the same number of degrees from TDC, that would put it at 107, but adding 107 + 107 = 214/2 = 107 and the cam cards indicates that the LSA is 112 degrees. That means that the exhaust centerline has advanced 10 degrees because the difference between the LSA and the intake centerline is 5 degrees. Placing the exhaust lobe centerline at 117 degrees puts the numbers in place:


117 + 107= 224 /2 = 112-degree LSA.


Now because we have so many Dual Over Head Camshaft (DOHC) engines in production today, let’s just take a second and discuss what the OE’s are doing for 21st century engines. Since a DOHC engine uses a separate intake and exhaust camshaft, this allows engineers to move the intake and exhaust lobes separately. So now with hydraulic adjusters, the ECU can move either cam separately to advance or retard the intake or exhaust. So for low=-speed driving, they advance the intake and retard the exhaust to maintain a sewing machine idle.


Then, somewhere in the midrange when the engine would really respond to lots of overlap, they begin to retard the exhaust to create more overlap. In reality, most of the DOHC engines only move the exhaust lobe for emission reasons. As an example, Fords Variable Cam Timing (VCT) engines only change one lobe while the Ti-VCT (Twin Independent Variable Cam Timing) moves both cams.


This is probably more than you wanted to know about camshaft positioning, but this might come in useful at some point. If nothing else, you can use it to dazzle your friends with you incredibly acute knowledge of camshafts and how they work. Or maybe not…


Here’s a breakdown of the advantages of advancing or retarding your cam timing:


Advance Cam Timing


  • Begins Intake Event Sooner
  • Opens Intake Valve Sooner
  • Builds More Low-End Torque
  • Decreases Piston-to-Valve Clearance
  • Increases Piston-Exhaust Valve Clearance

Retard Cam Timing


  • Delays Intake Closing Event
  • Keeps Intake Valve Open Later
  • Builds More High–RPM Power
  • Increases Piston-to-Valve Clearance
  • Decreases Piston-Exhaust Valve Clearance

  • I don't think that is the case in this situation 12 degrees?
 

340challconvert

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Thank you much for the information
I like to read on everything and always open to improving my skills.
I removed the cam/crank sprockets and relocated the cam to line up at the 12 / 6 positions with number one at TDC

I am assessing the cam specs that came with the engine; Summit 272-272 duration 454/454 lift, 110 lobe separation 52 degrees overlap, 216 216 duration @ .50 (1500-5200)
I have other cam options; 1. Comp cam 262/270, 462/470, 110w (1300-5600 power range) 2. Comp cam 268/280 .477/.480, 110 (1600-5800 power range). 3. Mopar Purple 248/256, 410/425 lift, 110. (1000-5000 power range).
I even have the option of using the stock cam from my A66 340 which is still in good condition.

The goal was to get a decent and fun engine in the car while I rebuild the 340. Not looking for total max performance. The specs of the cam that came with the engine was advertised as "fair idle with good power in the low to mid ranges. I would not mind going to the wider power rpm scale a little with the 262/270 Comp cam.
 

340challconvert

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Bret, yea, Mabco has mixed positive and negative reviews. I am checking the measurements and readjusted the cam/crank settings.
I figured for the price I got high compression flat top pistons, moly rings, 30 over, hardened rod bolts, and a 272 cam.
This will be a short term replacement engine while the 340 gets rebuilt.
It was tough to get an engine a year ago with the parts shortages, nothing was available. I had to wait 4 months for this one, so I pulled the trigger.
Thanks for your thoughts
Phil
 
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moparleo

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Phil,
Generally when advance is built into the cam, it will show up on the spec sheet, not with the camshaft out of sync with the crankshaft.
Otherwise the whole cam is out of sync.
I would just replace the cam. Much cheaper now and no question about the timing. You still need to degree it. Every cam, every time.
 
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