Does machining ~1mm off the B230 head result in poor idle quality (due to late camshaft events)?

[DET17]

That's my question of the day.

Been detailing my saga over in MAINT, as my 94 RB tractor engine is pretty much stock. However, I did machine .030" / 0.75mm off the head, and am running a COMETIC 036, which I understand is at least .010" thinner than the stock HG.

SO, my 4 banger is idling poorly.... I've gone thru all the usual suspects (detailed in MAINT). Using vacuum gauge analysis, about the only consistent cause which fits my symptoms is that of late camshaft events.

My 94 RB engine is using the stock round tooth belt sheaves. I understand that bringing the camshaft closer to the deck height, absolutely retards the camshaft events. What I do NOT know is if these changes (along with the A camshaft) are the cause of my poor idle vacuum levels.

Hoping to hear from those who have done the 1mm cut on their 530 heads, and learn if they had to advance their camshaft to regain quality idle. Mine is not horrific, not great..... 4 cylinders are still expected to idle at 17-21 inch HG.... EDIT - mine is steady at idle with 14 inches HG (retested with my new LISLE 20300 gauge).

What say ye, head shavers?

 

[shoestring]

I'm going to assume this is on LH2.4.

When I had this same combination years ago (disclaimer: stock head gasket and 1.0mm off head), I'll agree that you knew it was cammed, particularly in the first 60 seconds or so. I never took a vacuum reading on it, so I can't say how that compares.

To answer your question, I wouldn't think that the 3-4 degrees you've retarded this will make as much of an impact as the relatively long overlap the A cam offers, particularly at very low lift. It's a sportier choice than the M for sure, but it has its trade-offs.

You could try opening up valve lash to 0.020" and see how it responds: referencing my spreadsheet, that would cut 14 degrees out of your overlap if you're currently at 0.015"...OR, more scientifically, you could open it up to 0.020" on just the exhaust side, thereby leaving the intake closing the same, but reducing the overlap by 7 and seeing what the results of that test might be.

 

[DET17]

I'm going to assume this is on LH2.4.

Nope, Regina/REX. Thanks for the scientific recommendation ... if I find nothing else, I will open up that exhaust side (which I seem to recall ended up around .015 or .016").

 

[OttoB]

No. It will be fine

 

[Led]

I ran an A for years in a B230FT. I don’t recall it idling poorly. Mine was stock other than a 15g. I don’t remember what idle vacuum was other than it was in spec.

For reference my current B230FT with an exhaust and tune pulls 20 in HG at idle in park A/C off.

 

[DET17]

Bumping this situation:

My engine is running OK but vacuum is fair still (around 14-15 inches HG) at idle and it has some twitch. Engine compression is spot on at 175-175-172-175, so no mechanical deficiencies exist (pistons/rings/valve sealing).

With my stock head milled .030" and a Cometic 036 HG, I am a solid 4* retarded of the A cam..... everything I read in generic engine vacuum analysis states the simplest cause for what I'm measuring is "late camshaft timing". I attempted to use StealthFTi cam clearances and might have screwed the pooch with my results. With my personal collection of shims, I attempted to optimize the clearances but ended up with a range of .012 to almost .020 due to lack of shim thickness on hand. In my old Engineer brain (and the reply from Shoestring above)..... I'm thinking the tight valve clearances are causing the high pressure exhaust pulse(s) to reverse into the intake runner(s), causing my crappy idle vacuum.

SO, now it's time to fix it. I've spoken with STS about making me a custom Dale's type cam gear with 4* and 6* advance pin hole. What I need is a final simple solution, so I can put my 745 into reliable service and stop farting around with this tractor engine! All the chat in "camshaft measurement results" thread makes me wonder, do I need to degree this old A cam to get it right? Or just buy the 6* advance, single pin it, and be done? Finally, since the shaved head has me at net -4*, do I really want a +10* advance pin so that when the dust settles my A cam is at a real 6* advance in my REX/Regina engine? STS will make the single piece camshaft sheave/pulley to my requested advance value.

It seems the vacuum issue root cause might turn out to be camshaft timing events, with nothing at all to do with the 4* retarding of my setup.

 

[culberro]

Bumping this situation:

My engine is running OK but vacuum is fair still (around 14-15 inches HG) at idle and it has some twitch. Engine compression is spot on at 175-175-172-175, so no mechanical deficiencies exist (pistons/rings/valve sealing).

With my stock head milled .030" and a Cometic 036 HG, I am a solid 4* retarded of the A cam..... everything I read in generic engine vacuum analysis states the simplest cause for what I'm measuring is "late camshaft timing". I attempted to use StealthFTi cam clearances and might have screwed the pooch with my results. With my personal collection of shims, I attempted to optimize the clearances but ended up with a range of .012 to almost .020 due to lack of shim thickness on hand. In my old Engineer brain (and the reply from Shoestring above)..... I'm thinking the tight valve clearances are causing the high pressure exhaust pulse(s) to reverse into the intake runner(s), causing my crappy idle vacuum.

SO, now it's time to fix it. I've spoken with STS about making me a custom Dale's type cam gear with 4* and 6* advance pin hole. What I need is a final simple solution, so I can put my 745 into reliable service and stop farting around with this tractor engine! All the chat in "camshaft measurement results" thread makes me wonder, do I need to degree this old A cam to get it right? Or just buy the 6* advance, single pin it, and be done? Finally, since the shaved head has me at net -4*, do I really want a +10* advance pin so that when the dust settles my A cam is at a real 6* advance in my REX/Regina engine? STS will make the single piece camshaft sheave/pulley to my requested advance value.

It seems the vacuum issue root cause might turn out to be camshaft timing events, with nothing at all to do with the 4* retarding of my setup.

Why not use a standard adjustable timing gear, like what STS already sells?

 

[DET17]

Why not use a standard adjustable timing gear, like what STS already sells?

I certainly can. I asked Scott at STS to describe if the 2 pieces are "toothed" so they stay indexed together and don't rely on smooth faces and bolt clamping force. I recall some IPD gears from yesteryear that were made with the toothed style so you had mechanical engagement.

 

[culberro]

I certainly can. I asked Scott at STS to describe if the 2 pieces are "toothed" so they stay indexed together and don't rely on smooth faces and bolt clamping force. I recall some IPD gears from yesteryear that were made with the toothed style so you had mechanical engagement.

They are not splined/keyed together. The parts do have a very tight fit and have ample clamping force. I’ve never had one come loose with large cams and dual springs, and more revs than most. While I do understand your concern for the “what if” scenario, I don’t think it’s statistically likely to happen.

 

[dl242gt]

I certainly can. I asked Scott at STS to describe if the 2 pieces are "toothed" so they stay indexed together and don't rely on smooth faces and bolt clamping force. I recall some IPD gears from yesteryear that were made with the toothed style so you had mechanical engagement.

My original IPD adjustable gear is a stock gear cut around the inside with a slider piece added to make it adjustable. It's flat surfaces against each other. Never an issue. It's probably 20 years old now.

 

[sbabbs]

I got two cars with 30 thou taken off both LH 2.4 with turbo one with A cam and one with T cam both idle fine no problems. I'd look for vacuum leak. 95 turbo with T cam 30 thou off head with aftermarket boost gauge idles at 20 on the gauge. My 90 with factory boost gauge with barton sticker can't read it went full retard after a few years...

If I could only go back to stock... ha

 

[hessam69]

Can you show a video of the idle problem?

 

[DET17]

Can you show a video of the idle problem?

If I were smart enough! Video's I've recorded on PhotoBucket don't seem to play once placed there. Perhaps I need to find another suitable location for them rather than PB.

Basically the idle just dances between 14-15 inches HG.... normal 4 cylinders should be around 18-21 from what I read. I may have an intake gasket leak which I'm going to attack here in the next couple of days (new Penta gasket unhand) so that is the last stone unturned regarding vacuum. The only snake left in the woodpile is then late camshaft events, and likely "too tight" clearances when I shimmed the A cam.

 

[hessam69]

That does seem like a vacuum leak.

I’d love to see a video of the vacuum and also the tachometer at idle.

 

[OVERDRIVE]

It just sounds like Regina (map based) with a cam that has a generous amount of overlap for what it is. The A is still small, an intake valve closing event that's around where a V is won't make it idle bad.

 

[OttoB]

I had a idle issues with my B230FK and 1,2 mm shaved cylinder head. A vacuum leak was find. Idle got better, but not 100% smooth. Guilty #2 was a grounding issue, especially between alternator and intake manifold. Bad grounding makes alternator crazy. Voltage jumps up and down and LH tries to compensate that.

 

[DET17]

Yesterday I replaced the twice used intake gasket with an NOS Penta one; same time I changed my injectors for a pro rebuilt & flowed set of 960/850 injectors...Bosch yellow "746". Same exact result.... vacuum at idle sitting at ~ 14 inches HG. Photobucket movies are not approved here, so a pic:



Now with every stone overturned, I'm convinced the root cause of my vacuum condition is the A cam, and cam timing retarded the 4*. Since I have to go into the cam to remedy this issue, I might as will fix it properly and replace with a T cam with 6* of advance for my NA application.

REX/Regina has nothing to do with my low vacuum issue.... car starts instantly and idle timing sits solid at 12* BTDC.

Thanks folks for the feedback.....

 

[DET17]

Well, the answer is now clear: NO, machining the head does not cause lower than expected vacuum readings measured at idle speed.

And YES, installing the A cam (with its large overlap) and approx. 4* retarded timing relative to the crank & pistons, does cause lower vacuum.

Confirmed this today.... installed a T cam (thanks to Overdrive), advanced the timing net 6* at the cam... and now the same engine reads 17.5 - 18.0 inches HG at idle.

While the "late camshaft timing" certainly contributed to reduced vacuum, the balance of the increase came by virtue of the T cam and it's much reduced overlap (in comparison to the A).

 

[DET17]

One more thing..... a correction.

Thanks to @shoestring, who informed me I had mistakenly over advanced my T cam rather significantly.

My target was 4* of advance for the head machining (and Cometic 036 gasket thickness reduction from stock gasket).... plus I thought I'd throw in another 2* advance to hopefully give the T more torque down low (not detected on the wet test drive).

Mr. Shoestring noticed in the above pics, that I had actually advanced the camshaft 6*.... which translates to 12* advance from the crank. All of us gear heads know that the crank rotates twice for every single camshaft rotation.

While I knew the oft repeated TB advice that claims "1* of timing retarding for each .010" of distance removed between the camshaft and the crankshaft..... but didn't know that the 1* was CRANKSHAFT degrees per each .010" removed! Somewhere in the urban TB legend quoting and re-quoting, the CRANK reference vanished and it simply was repeated as 1* lost per .010" reduction.

Having now been properly educated to this fact, I have revised my STS adjustable timing pulley and have properly advanced my T cam 2*, which nets 4* at the crank. Please share this information with folks in pertinent camshaft threads. Here we go, now +2* and perhaps a smidge more.......

Hope this helps another red block camshaft find the proper timing.

 

[OVERDRIVE]

Yep, each hash mark on an STS gear is 2° as measured at the crank. A while ago I did the math and it comes out to 1° crank for every .020" removed. That's not what other people quote from real world experience, but it's generally what I followed at first until I just ended up checking everything by intake lift at TDC.