Correcting Cam Timing with a Decked Block/Milled Head Flat-4 Motor

[Rasmus]

Contemplating my build, it came to my attention that after I visit my machine shop my block will probably get decked and heads most likely milled to bring them back to flat from whatever thousands they were off. But decking and milling make the distance from the crank pulley to the timing cams just a bit shorter. This will retard the timing of all four camshafts. Although I could run a thick head gasket, that just seems like a band-aid. I've only ever heard of someone running thicker head gaskets because they've exhausted all other better options. Plus HG's only come in step widths. If you need a width in between you're SOL.

My build is running AVCS on the intake. So while I could get adjustable cam gears for the exhaust I'm using Subaru Parts for the AVCS. And with all the advantages AVCS gives, disabling it seems silly.

That bring me to these:




Adjustable Idlers Pulleys. The first two pictures are the offering from Crawford Performance. The third is from LIC Motorsport.

Here's a copy of the instructions from LIC on how to install these:

LIC Motorsports Adjustable Timing Idlers
These parts are designed for longblocks that have been narrowed down from resurfacing the heads
during a rebuild or decking the block and/or both. When that process is done it effectively retards the
timing, this is because the belt has not changed length and something needs to make up that difference
in the slack (the tensioner can only do so much), and likewise if you have different thickness
headgaskets, these are perfect in conjunction with that, as the same issue is present (just vice versa,
which is a lengthened block).
This is what the LIC Motorsports adjustable timing idlers were designed for and is only recommended to
bring your cams back into proper alignment.
For Reference:
Upper Idler: This upper idler when adjusted effects the RIGHT (Passenger side) intake/exhaust cams.
Lower Idler: This lower idler when adjusted effects the LEFT (Driver side) intake/exhaust cams.
10mm Hex: Is there to maintain proper alignment while tightening bolt.
How it all works:
When*installing*these*aftermarket*adjustable*idler s,*you*will*follow*the*same*steps*as*doing*an*OEM
timing*belt*install;*this*consists*of*following*pr oper*order/alignment.
Step*1-*Crank*always*must*be*in*proper*alignment*(this*is *reference*point)
Step*2-*Adjust*upper*Idler*to*align*right*side*cams,*snug *14mm*bolt.
Step*3-*Adjust*lower*idler*to*align*left*side*cams,*snug* 14mm*bolt.
Step*4-*Once*proper*alignment*is*confirmed*pull*pin*on*te nsioner.
Step*5-*Rotate*crank*two*full*revolutions*(clockwise).
Step*6-*Stop*at*crank*timing*mark,*confirm*proper*alignme nt*(if*cams*are*not*aligned*properly,*adjust
idlers*as*necessary*until*proper*alignment*is*obta ined.**
Step*7-*Torque*adjustable*idlers*to*45*ft.*lbs.
Step*8-*Confirm*accurate*timing*marks*with*doing*two*full *revolutions*before*installing*timing*covers.
:
Notes:
• These are a single roller bearing design
• Street cars should replace every 60k miles
• Race/Track cars should replace yearly and/or each engine teardown

Crawfords run $75 per from ebay, need two, so $150. LIC's run $175 for two from RallySportDirect.

What's the forum's thoughts? Any better way to correct timing due to block decking and/or head milling? Known issues?

[Scargo]

From all I've read, and experienced, the stock head gaskets are the known, reliable, real deal you can go to the bank with. I doubt you need to change anything to compensate for a slight compression ratio increase so I would stick with that gasket. From what I gather, there's nothing wrong with the CR creeping up and some like to do that in lieu of more boost. I think it's more low end torque that you gain.
If there's no cheap way to adjust the cams at the pulley (offset pins?) then I see nothing wrong with the adjusters. It's probably the most cost effective, straightforward way of doing it that I can think of. Could just get bigger cams and not worry about the small timing discrepancy.... $600 more new. There might be some deals out there.

[Jaime]

Why not get proper adjustable cam gears? I'm new to Subaru engines, so maybe it's not done often on these, but degreeing cams is a pretty standard engine build step. As an added benefit, you have the possibility of moving the power band around a bit.

[Rasmus]

Why not get proper adjustable cam gears?

The cam gears you've linked only adjust the Exhaust Cams. And those are some very pretty pieces. Nice find. But what about the AVCS Intake cams?


The AVCS is in the cam pulley. Remember the distance the timing belt has to travel from the Crankshaft Cam to the Intake Cam is shorter on a milled/decked flat-4. How do you fool the intake cam to be where it should be with the modified length?

[Rasmus]

From all I've read, and experienced, the stock head gaskets are the known, reliable, real deal you can go to the bank with. I doubt you need to change anything to compensate for a slight compression ratio increase so I would stick with that gasket. From what I gather, there's nothing wrong with the CR creeping up and some like to do that in lieu of more boost. I think it's more low end torque that you gain.

For me, I'd take more CR over Boost. I'd take timing over boost.

[Bob_n_Cincy]

Hey Rasmus,
The cam angle sensor are right on the intake cams. So the avcs will automatically adjust the proper cam angle no matter the belt length.
Did I miss something in you explanation of the problem.
Bob

[Rasmus]

The cam angle sensor are right on the intake cams. So the avcs will automatically adjust the proper cam angle no matter the belt length.
Did I miss something in you explanation of the problem.

Nope. But that sound you just heard was me being enlightened. Love that. I had no idea the ECU could do that with the AVCS. Feel a little silly not understanding it before.

If that's the case then all I have to do is get the two exhaust cams lined up and let the ECU run the intake-cam-show. So I'll still have to use this product but only to correct exhaust timing.

[Rasmus]

I love this feeling of new knowledge and understanding. One of the best feelings in the world.

Just found this old post on Nabisco from Crawford:

Would you not need dual avcs to control each individual cam?

Nope, you can move the exhaust cam with the adjuster and advance the intake with the AVCS.

Brilliant!

[Scargo]

When you do all this shaving which way does the inaccuracy go? Retarded or advanced? I'm guessing it gets retarded. How much?
AVCS is pretty well documented on NASIOC or IWSTI. Seems you would limit AVCS's upper range if it has to correct for the misalignment first (if that's what it does). I believe some have moved the sprocket one gear tooth to create more initial advance. Which sprockets? I dunno.

I found this.
Rallispec says about degreeing Kelford cams:
What is "degreeing in the cam" and do I need to do it? Degreeing the cam means setting the cam timing to the match the specifications of the cam manufacturer. Milling the cylinder head or block deck as well as manufacturing variations can result in cam timing errors. While it is a good idea to check the cam timing using a degree wheel, actually correcting any errors can be difficult without adjustable cam gears. Moving the cam sprocket one tooth on the timing belt may allow for correction of major errors but errors smaller than 1 timing belt tooth would require modifying the sprocket keyway or dowel.

Advancing the cam by 1 tooth =7.5° cam timing.
AVCS allows for 38-40 degrees of advance on the Intake cam. This is the amount of variable overlap you can have between intake and exhaust.

I've seen lots more on this; just can't find much this evening.

[Bob_n_Cincy]

I love this feeling of new knowledge and understanding. One of the best feelings in the world.

Just found this old post on Nabisco from Crawford:




Brilliant!

The milling of heads would bring the heads closer to the crank (pulling the cams) so the cams would be retarded a little bit on cylinders 1 and 3 and triple that much on 2 and 4.

AVCS on intake cams will only correct the intake cams.
I believe some Subaru engines have avcs on exhaust also. that would be a different story.
Bob

[Rasmus]

When you do all this shaving which way does the inaccuracy go? Retarded or advanced?

Milling and Decking retard the timing. "The shorter the deck the more you ride the short bus."

[Bob_n_Cincy]

Hey, Lets not make jokes about one of my hero's.
JF%20Overhaulin%20web.jpg

[Rasmus]

Join us for an extra special episode of Chip Foose's Overhaulin'

[JeromeS13]

+1 for LIC. I use the LIC Motorsports version on my 818 and my previous STI. My other friends also run the LIC version. Noah and Adam at LIC are great guys!

[ssssly]

Lic stuff is great. I have had nothing but positive results. (I am in no way affiliated with Lic).

JDM intake AVCS cams can adjust to 45 deg. More than you ever need. So that's another option.

The bigger issue you need to be careful of when decking Subaru blocks and heads, is that you often need custom pistons and combustion chamber porting on the heads. Your "stock" head and block decking often moves the quench of the engine into the head gasket. So without either adjusting stroke or pin to face depth you end up with a head gasket blowing monster on your hands.

Generally if I deck a Subaru block and heads I stroke (EJ20) or destroke (EJ25) it to eliminate this issue. And its a good excuse to build a stroker, which just sounds cool.

It depends on how much you are taking off. Something to discuss with your machine shop and builder though.

[Evan78]

Does anyone know how much we're talking about here? Can we equate X thousandths off the block to Y degrees of retard?

[Ironhydroxide]

I recently went through some of this when i Decked 0.086" (yes you read that right) from each of my EJ25D heads to up my compression ratio from 8.5:1 to 9.3:1.

some simple info for those that want to play with calculations.
the belt is an 8mm Pitch belt. the Crank Gear has 24 teeth, which also means the Cam gears are 48 Teeth.

48 teeth at 8mm a piece would make the whole cam gear 384mm in circumference.

Now, if you decked your heads, say 0.010" then you would need to pull a total of 0.040" (1.016mm) extra out of the belt with the tensioner.

as the tensioner is between the crank gear and the driver side cam gear, all this extra length would be removed there. causing both drivers and passengers cam gears to be retarded.

so, first. starting at the crank gear. moving BACKWARDS in belt rotation (so we can get an accurate estimation of how much retard we get out of decking) we travel across the crank gear, and then under the idler. pass the head surface where we've removed 0.010" (0.254 mm) from the length the belt has to travel. meaning the Alignment mark is therefore 0.254mm further to the passenger side of the vehicle at the belt surface.

now if we want to find the DEGREE of retard for this, we need to take the total circumference of the gear (384mm) and divide that by 360, so we get MM per Degree of rotation. giving us 1.0666mm per Degree of Cam rotation.

now we take that degree of rotation and do some more maths to it, and we figure out that if 1.0666mm is 1 degree then 0.254mm is 0.238 Degrees of retard at the Passengers intake cam. now the distance between the passengers intake cam and passengers exhaust cam hasn't changed, so the passenger exhaust cam is ALSO 0.238 Degrees retarded.

on to the Drivers side. leaving the passenger exhaust gear, we AGAIN pass the 0.010" head decking surface, move over an idler, under an idler, over the water pump and pass the other side 0.010" head deck surface. making the Drivers side exhaust gear 3x 0.010" retarded (or 0.762 mm) when we do the same maths from above with the degrees per mm, we get a retard of 0.714 Degrees. this is also the same for the Drivers Intake gear.

and now to finish the circuit, we pass the 0.010" decking surface, under an idler, and under the tensioner (which has to move roughly twice the head decking FURTHER than normal. ) and back to the crank gear.

so, the TL: DR version is:
at 0.010" head decking per side, the passenger cams are 0.238 Degrees retarded, and the Drivers cams are 0.714 Degrees retarded.
and the tensioner will need to move roughly twice the amount of head decking FURTHER to tension the belt.

now there are a few ways to solve all of this. One; take your idlers to a machine shop and have a specific thickness sleeve pressed on to the bearings (a thickness you calculate, to counteract that retard). Two; Buy the adjustable idlers, which "work" but are only as good as the setup, and CAN and DO slip over time. Three; Get adjustable cam gears, assure you're not going to be maxing out the tensioner, and set the cams off a degree wheel on the crank.

in my extreme case I went with a tooth SHORTER belt (as my 0.086" took a total of 8.7376mm out of the belt) AND the adjustable idlers, as I didn't have the $$ to have sleeves pressed on to the idlers AND nobody makes adjustable cam gears for the Phase 1 DOHC Engines.