What do I need to know about installing a more aggressive cam?

[Pete Whitstone]

Why would shaving the head or box result in you needing to degree the cam to get it back to zero? I'm don't quite see how the geometry changes so that would be required. Shaving the head will increase CR, but not change the relative cam to crank angle . . . same as shaving the box. Sorry if I'm asking obvious questions.

It does change the cam timing. If you think about it, what you have done by shaving the head or cam box is move the 2 pulleys closer to each other. If you think of the belt as running in a straight line between them, then you can envision how the teeth would no longer line up as you move the 2 pulleys closer to one another. So if you envision the crank pulley staying in the same location, in order to get the cam pulley to line up with the belt after shaving, you must rotate it slightly. That rotation is what changes the cam timing, and is what an adjustable cam pulley can correct for.

Pete

 

[aarpcard]

It does change the cam timing. If you think about it, what you have done by shaving the head or cam box is move the 2 pulleys closer to each other. If you think of the belt as running in a straight line between them, then you can envision how the teeth would no longer line up as you move the 2 pulleys closer to one another. So if you envision the crank pulley staying in the same location, in order to get the cam pulley to line up with the belt after shaving, you must rotate it slightly. That rotation is what changes the cam timing, and is what an adjustable cam pulley can correct for.

Pete

Gotcha. That makes sense. Wasn't thinking about the teeth on the belt.

 

[dllubin]

Ahh I think I get it now. You'd degree the cam to get the 0 degree alignment to match back to the stock cam profile if the new cam is off.

Why would shaving the head or box result in you needing to degree the cam to get it back to zero? I'm don't quite see how the geometry changes so that would be required. Shaving the head will increase CR, but not change the relative cam to crank angle . . . same as shaving the box. Sorry if I'm asking obvious questions.



The max end of the range is 5.05mm. I noticed that MWB sells shaved boxes too. Didn't really want to go that route unless it made sense for my use case as they're kind of pricey and I'd have to buy new shims either way. (not worried about valve float because I don't plan on high revving the motor often. Although I don't really know at what rpm valve float would begin to be an issue.)

Auto Ricambi sells them up to 5.20 mm.

 

[EricH]

Why would shaving the head or box result in you needing to degree the cam to get it back to zero? I'm don't quite see how the geometry changes so that would be required. Shaving the head will increase CR, but not change the relative cam to crank angle . . . same as shaving the box. Sorry if I'm asking obvious questions.

Either one reduces the distance from the crank pulley around the aux sprocket to the cam drive sprocket. That in turn changes exactly where the teeth in the cam belt fall on the sprocket; if you keep the same belt tooth in the same slot on each sprocket, the cam will be slightly retarded.

 

[Andy]

Shaving moves the cam and crank gear closer together if you shaved a lot you could simply move the timing belt one tooth, but you dont want to shave that much off.
Adjustable cam wheel lets you precidsely set cam and crank timing.

Another alternative that i thnk was mentioned is lash caps. They are small (about the size of a dime) caps that fit on the tip of the valve stem. Many folks feel they add too much mass to the valve train, but I feel the add less mass than thick shims. I ran them in my 1500 autocross motor and never had any problems. A lot cheaper and easier than shaving cam towers.

http://www.midwest-bayless.com/p-17...-set-for-8mm-stem-fiat-dohc-sohc-all-new.aspx

 

[Dr.Jeff]

Why would shaving the head or box result in you needing to degree the cam to get it back to zero?

When the cam becomes physically closer to the crankshaft (e.g. shorter head and/or shorter cam box...both the result of shaving), the two timing belt pulleys (crank and cam) are now closer to one another. But the belt is still the same length, therefore something has changed between the relative belt length and pulley ratios. This has the effect of rotating the pulleys toward one another as the belt tensioner takes up the excess slack in the now longer (relatively) belt. Rotate a pulley, change the cam timing. In some cases a larger diameter timing belt tensioner roller (bearing) is used (e.g. 1300 roller in 1500 engine) to allow for excessive differences between the belt length and pulley positions (like when a LOT of the head is milled to significantly increase the compression ratio). This is done to assist the limited amount of travel allowed by the tensioner. But the cam timing still needs to be corrected (as you said, bring it back to zero).

MWB sells shaved boxes I see

I noticed that MWB sells shaved boxes too

Be aware the shaved cam boxes listed on their site are actually shaved MORE than the amount required to make up for the decreased base circle on a reground cam. This now requires THINNER than stock shims to compensate for the excess shaving. So these pre-shaved boxes are NOT going to bring things back to stock (as far as shim thickness). And therefore non-stock shims are still required. As far as I know the only way to get thinner than stock shims is to have them ground down, which might remove some of the hardened contact surface. They do this for racing applications where thinner than stock shims may offer a minuscule performance advantage at extremely high RPM's (due to slightly less weight in the valve train). However you might contact them to see if they will custom shim a cam box only enough to compensate for the decreased base circle AND allow the use of stock range shims.

If you have the head completely* rebuilt as part of this engine refresh, then a cam box that is shaved (skimmed) only enough to compensate for the regrind cam (with stock shims) might be a good idea. Because it will assure the surface of the cam box is straight and square (if it has been properly skimmed). *Note I said "head completely rebuilt". By that I mean all surfaces of the head (including the interface with the cam box) have been skimmed to be flat and square.

 

[rx1900]

Yes - as others have said - shaving the cam box and/or head WILL result in the cam timing being slightly retarded. This is generally not a good thing. If anything, on these engines you would want the cam timing to be slightly advanced for better performance. General consensus is that about 2 degrees advanced is ideal. Zero is just fine. Anything retarded is bad.

Having said that - you probably would not notice a couple of degrees retarded outside of a dyno test. And thus probably not worth the hassle and expense (by using an adjustable cam pulley) to correct it. At least for the small amount of cam box milling you would be likely to do.

If....you are sure you can obtain correct valve clearance by using shims in the 4.9 to 4.9mm range, you will probably be okay. Shims are available up to 5.05mm. Yes you at right near the top of available shims, but probably okay. In the future, any wear will most likely result in the valves recessing a bit and thus requiring thinner shims for any future valve adjustments. Yeah, the thicker shims are a tad heavier, but unless you are racing or using constant very high RPMs , I dont think it is worth the hassle and expense to shave the cam box to allow thinner shims. Which would also then alter your cam timing for the worse.

However..having said that...I would highly advise you to check two other things first !! The stock gasket between the head and cam box is just a thin paper gasket. It works just fine....BUT....only if both the mating surfaces are PERFECTLY flat. You said earlier the bottom of you head was warped and you had it machined straight and flat. That is good...but..often in this case the TOP of the head - where the cam box bolts onto - is also warped and no longer perfectly flat !!! Your machine shop should have checked this, but often they dont. And/or your cam box may be warped too. If either the top of the head or the bottom of your cam box are not perfectly flat, then that thin paper gasket will NOT seal that joint perfectly, and you will leak oil from there. Which can be very annoying.....

So..if and only if...you need to have the head and/or cam box machined to make them flat again..do it. This will also bring your required shims down to a better range. Other than that.....dont bother.....

 

[aarpcard]

Thanks for all the great answers!

Yes - as others have said - shaving the cam box and/or head WILL result in the cam timing being slightly retarded. This is generally not a good thing. If anything, on these engines you would want the cam timing to be slightly advanced for better performance. General consensus is that about 2 degrees advanced is ideal. Zero is just fine. Anything retarded is bad.

Having said that - you probably would not notice a couple of degrees retarded outside of a dyno test. And thus probably not worth the hassle and expense (by using an adjustable cam pulley) to correct it. At least for the small amount of cam box milling you would be likely to do.

If....you are sure you can obtain correct valve clearance by using shims in the 4.9 to 4.9mm range, you will probably be okay. Shims are available up to 5.05mm. Yes you at right near the top of available shims, but probably okay. In the future, any wear will most likely result in the valves recessing a bit and thus requiring thinner shims for any future valve adjustments. Yeah, the thicker shims are a tad heavier, but unless you are racing or using constant very high RPMs , I dont think it is worth the hassle and expense to shave the cam box to allow thinner shims. Which would also then alter your cam timing for the worse.

However..having said that...I would highly advise you to check two other things first !! The stock gasket between the head and cam box is just a thin paper gasket. It works just fine....BUT....only if both the mating surfaces are PERFECTLY flat. You said earlier the bottom of you head was warped and you had it machined straight and flat. That is good...but..often in this case the TOP of the head - where the cam box bolts onto - is also warped and no longer perfectly flat !!! Your machine shop should have checked this, but often they dont. And/or your cam box may be warped too. If either the top of the head or the bottom of your cam box are not perfectly flat, then that thin paper gasket will NOT seal that joint perfectly, and you will leak oil from there. Which can be very annoying.....

So..if and only if...you need to have the head and/or cam box machined to make them flat again..do it. This will also bring your required shims down to a better range. Other than that.....dont bother.....

Good point about the head to cam box mating surfaces - I'll double check to make sure those are flat as well.

 

[Squirrelmonkey]

Cam Timing is all about where you want your power to come in at..Advancing the cam brings the power in at a lower RPM range. Retarding the cam brings the power at higher RPM's. Most stock grind spec cards have an advance added to the timing numbers. Performance or race cams don't..So retarding the cam is not a bad thing at all. It's just not suitable for stop and go city driving. Regarding cam box milling vs Thicker shims etc..The best solution in my experience is to use lash caps. they reduce the valve train masses greatly..Valve shims are heavy as hell compared to lash caps.
The physics regarding mass x acceleration etc. come into play here where valve float is concerned..If you don't run your engines to redline often if not always then It doesn't matter much.

 

[Deane]

When you shave the cam box it drops the cam drive pulley down closer to the crank shaft pulley, hence the drive belt tooth count is not exact as stock, not out a tooth or anything but does turn the cam in relation to crank just a little so that when tensioned it is not exact as stock, like I mentioned I have no problem performance wise, but do have the 1300cc idler pulley to take up the extra slack in belt. Ignition is set to 10deg BTC vacuum disconnected. Hope this makes sense.

 

[aarpcard]

When you shave the cam box it drops the cam drive pulley down closer to the crank shaft pulley, hence the drive belt tooth count is not exact as stock, not out a tooth or anything but does turn the cam in relation to crank just a little so that when tensioned it is not exact as stock, like I mentioned I have no problem performance wise, but do have the 1300cc idler pulley to take up the extra slack in belt. Ignition is set to 10deg BTC vacuum disconnected. Hope this makes sense.

What's the rationale behind disconnecting the vacuum advance?

 

[Eastep]

The best solution in my experience is to use lash caps. they reduce the valve train masses greatly..Valve shims are heavy as hell compared to lash caps.
The physics regarding mass x acceleration etc. come into play here where valve float is concerned..If you don't run your engines to redline often if not always then It doesn't matter much.

I Rev the piss out of my car. Infact, I only drive my X1/9 when I want to pretend I'm a '70s F1 driver or in a road race championship. I'm about to do a shim adjust to my car, as there is a bit of lifter noise that cropped up the last month of driving season. I would very much like more info on lash caps and advantages and disadvantages of making the switch, & what's involved. A lighter valvetrain only promotes higher revs and less wear. I like revs Are these caps readily available for the X1/9?

 

[kmead]

Steel lash caps are available from all of the Fiat vendors in addition to the many racing sources. Many cars use 8mm stemmed valves so you should be able to get what you want from a variety of sources.

Titanium ones are a bit less available but would be highly desirable.

 

[Dr.Jeff]

What's the rationale behind disconnecting the vacuum advance?

I'll let "AARP" speak for himself, but I think he was saying he set the timing with the vac hose disconnected, as per the factory manual instructions, then reconnect it after it's set.

 

[Dr.Jeff]

Steel lash caps are available from all of the Fiat vendors in addition to the many racing sources.

I assume lash caps are available in different thicknesses? I guess a little measuring and math should be done to determine the best thickness for the caps, working with the shims to get the desired final settings. One of the Fiat sources seems to offer only one thickness and recommends grinding down the valve stems to get the correct height. This does sound like a good solution to me. But I'm sure there are better options available?

 

[kmead]

The ones I have seen are in the 1.5mm range of thicknesses (.059”) so that would be the amount you could remove from the heavy steel shim on top of the bucket. A pretty decent trade off.

 

[Andy]

Grinding is not needed, a touch with a file is all I needed on my valve stems when I used lash caps.

 

[Dan Sarandrea (Phila)]

The ones I have seen are in the 1.5mm range of thicknesses (.059”) so that would be the amount you could remove from the heavy steel shim on top of the bucket. A pretty decent trade off.

I don't know that you can assume that, say, a 1.5mm lash cap lets you reduce shim thickness by the same amount. Because the bucket has a recessed area into which the shim drops, you have to allow for the possibility that a too-thin shim might not provide enough clearance for the cam lobe to make a full circle without fouling on the edge of the bucket. Without anything in front of me to look at, I would guess that the minimum shim thickness would have to = [whatever the height of the recess in the top of the bucket is] + [a little more so that the top surface of the shim is always "above the rim" of the bucket]. Looking at the parts catalogue, the skinniest shim thickness that is listed is 3.25mm part #4204141, which might be Aurelio Lampredi's way of telling us that's the minimum shim thickness to prevent the cam lobe from hitting the edge of the shim bucket.

If a hypothetical valve clearance required a 4.00 shim, then a 1.5mm lash cap could theoretically allow a 2.50 shim to be used, saving 37% of shim weight. But if the minimum allowable shim thickness is 3.25, then the valve tip would have to have 0.75mm taken off the top, and the shim weight reduction would be about 20%.

 

[Dr.Jeff]

For me, not only would I want a shim thick enough to allow proper cam contact as Dan describes, but I would also want to use shims within the standard range of available thicknesses without modification (i.e. without grinding them down)...aka 3.25 to 4.80 (I believe this is the standard Fiat range). Likewise I would not want to grind (or file) down the valve stems in order to use lash caps. The only reason I see for using lash caps on a relatively stock street engine is if standard thickness shims cannot be used to make up for the loss of cam base-circle diameter (when using a aftermarket cam, like the Euro-spec equivalent one described at the beginning of this discussion).

Therefore the proper shim/lash cap thickness in this case would be the net difference after: 1) cam replacement with smaller base circle, 2) resurfacing the head and cam box for trueness, 3) valve and seat refinishing, 4) proper clearance gap setting. Preferably a combination of thin lash caps and stock range shims (as stated above) could be used to achieve this net thickness; ideally this combination would utilize lash caps that allow the resulting shim sizes to fall toward the lower to middle range of thicknesses (say around 3.30 to 4.00 for example). However if lash caps are not available in a correct thicknesses to allow this, then thicker than stock shims (4.80 to 5.20) would be the next best answer in my opinion.

In regard to any advantages of using thinner shims. For a non-racing engine I view this as a trade-off. On one hand you are removing a minute amount of valve train weight with the thinner shims, on an engine that really won't benefit significantly from it in normal street driving. On the other hand you are either modifying standard components by grinding off critical contact surfaces, and/or you are creating a non-proper contact between the cam and shim/bucket (as described by Dan). To me this trade-off is not worth it. It might be different if we were building a full "performance/race" engine to be run at red-line all the time and real world longevity/reliability was not a concern; e.g. a very radical cam, fully ported big valve head, lightened rotating components, aftermarket pistons and rods, very high compression, etc., etc..

 

[kmead]

Agreed. This suggestion was about a having reduced diameter cam (reground) which necessitated either a milled cam carrier to bring the cam down to close enough to the bucket for shims into the standard shim range or adding lash caps to bring the bucket back up into standard shim range, in preferably the lower part of the range. Either way, lash caps are another part that might be used to solve a problem, just not all problems.