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Thread: Why does an 8psi turbo on stock motor blow a new headgasket, twice?

  1. #26
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    Quote Originally Posted by Vermont320i View Post
    Attachment 680237 It looks like there are some small stamped numbers on the head- would that mean it hasn’t been cut before?
    That head appears to have a crack between the water jacket and exhaust valve on #3. Possibly even another crack, top left'ish on the picture.
    Last edited by epmedia; 10-29-2020 at 05:46 AM.
    Tbd

  2. #27
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    Great catch, thank you. Yes, I just went out to the garage and checked it—-definitely a crack there.

    More info for the discussion with CHI today.

  3. #28
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    gotta be getting cold in that garage these days. good luck with the upgrades.

  4. #29
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    Quote Originally Posted by Vermont320i View Post
    Great catch, thank you. Yes, I just went out to the garage and checked it—-definitely a crack there.

    More info for the discussion with CHI today.
    I have cracked three heads now in the #2 and or #3 exhaust ports, heads get hot there. Mine where all stock N/A engine revving to 6,800 to 7,200 rpm.

    Auto-xing.

    Always FUN TO DRIVE - Build Thread & Tech info - 79 320/6 track car build thread -- Videos of track car -Adam in car Auto-x video - Start-up video - 4/2011 Adam's TOP BMW time San Diego BMWCCA - 4-5-15 Dyno break-in run new M20B25 - Exhaust Thread - Link

  5. #30
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    Good news, CHI is covering the repairs and making sure the surface isn’t warped on the head. I pay return shipping.

  6. #31
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    CHI is a good company...

    Randy

  7. #32
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    Agreed, and it’s already on its way back to me. All I am paying is return shipping.

  8. #33
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    Slight correction: CHI is a GREAT company. Head back from CHI, they could not weld up the other one so they resurfaced and rebuilt my old core they still had, for cost of shipping. Great to deal with quality people!

    After resurfacing, height of head is near minimum—-5.065”. I’ll Have to remember to check it with the top timing chain cover, too. I decided to use the ARP head bolts instead of standard, so those are going back to Pelican Parts.

    Questions: Given the minimum head height, should I go with a thicker than normal MLS headgasket instead of the standard Elring cutting ring gasket I bought (that can also go back to Pelican)? A special order MLS can be obtained from Ireland Engineering, there may be other sources, too.
    Should I use a standard type gasket but thicker—-VR makes a 1.8mm gasket? others?
    If a standard gasket compresses to 1.3mm/0.051”, what thickness would work for an MLS or other replacement?

    Factors: potential compression increase due to minimum thickness of head; head now near minimum, so cutting ring gasket would mean the head is junk (maybe, not sure) if I ever have to remove it again (hopefully not, but you never know).

    I’m trying to read up on the effect on the effect of all this on compression ratios, but it is making my head spin!

    Thanks,
    Bill
    Last edited by Vermont320i; 11-14-2020 at 07:26 AM.

  9. #34
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    Quote Originally Posted by Vermont320i View Post
    Slight correction: CHI is a GREAT company. Head back from CHI, they could not weld up the other one so they resurfaced and rebuilt my old core they still had, for cost of shipping. Great to deal with quality people!

    After resurfacing, height of head is near minimum—-5.065”. I’ll Have to remember to check it with the top timing chain cover, too. I decided to use the ARP head bolts instead of standard, so those are going back to Pelican Parts.

    Questions: Given the minimum head height, should I go with a thicker than normal MLS headgasket instead of the standard Elring cutting ring gasket I bought (that can also go back to Pelican)? A special order MLS can be obtained from Ireland Engineering, there may be other sources, too.
    Should I use a standard type gasket but thicker—-VR makes a 1.8mm gasket? others?
    If a standard gasket compresses to 1.3mm/0.051”, what thickness would work for an MLS or other replacement?

    Factors: potential compression increase due to minimum thickness of head; head now near minimum, so cutting ring gasket would mean the head is junk if I ever have to remove it again (hopefully not, but you never know).

    I’m trying to read up on the effect on the effect of all this on compression ratios, but it is making my head spin!

    Thanks,
    Bill

    If really want to see you'd need exact numbers and input into a volume calculator. I've my own spreadsheet for this but here is a basic online one to use that many have used in the past.
    http://www.csgnetwork.com/compcalc.html

    Basically you need to measure piston above or below deck height to really skew compression numbers. Example if piston is below deck which most stock M10's are, then the thickness of gasket compression doesn't have as drastic effect (just example +0.2 compression per .010"). Once reach piston above deck however the numbers skew fast and can add 1 full point of compression in some cases with -.040" gasket compressed difference.
    It's best to actually measure, then can plug numbers back and forth with the calculator to see what I mean.
    Same for shaving the head decreasing the chambers. Taking off .040" for example is almost good for +1 point.

    Another factor is head torque method used. I feel the newer angle method is higher clamping load meaning slightly a few thousandths more compressed gasket. Best way to really know compressed gasket thickness is a actual mock up torqueing of a head and using a feeler gauge between the head and block. There is a pad area between head and block to shove feelers into and measure exactly.
    Last edited by autox320; 11-14-2020 at 07:39 AM.
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  10. #35
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    A Couple of items,, use modeling clay to measure your clearances- valves to piston, since your deck height has come down use the lower end of the torque when tightening the timing chain tensioner, as too the upper timing chain cover if it was not ground down you'll need to sand down the top so that it matches the cylinder head so that valve cover will seal both on top--I have done this before..


    Randy

  11. #36
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    Quote Originally Posted by 320iAman View Post
    A Couple of items,, use modeling clay to measure your clearances- valves to piston, since your deck height has come down use the lower end of the torque when tightening the timing chain tensioner, as too the upper timing chain cover if it was not ground down you'll need to sand down the top so that it matches the cylinder head so that valve cover will seal both on top--I have done this before..


    Randy

    No offense but nah wouldn't use clay for PV clearance measuring. It's messy and not accurate. Clay is more for interference fit issues. PV is best checked with some cheap test springs installed on cyl1 valves, set lash of valve adjustment to zero, then dial gauge on valve spring hat. Roll to TDC mainly, then +/- 5, 10,15 deg and push by finger to see what ya got. Stock piston, stock motor with stock/mild cam will be "miles away" with PV clearance ie +.140" range.
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  12. #37
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    Pistons are not above deck height on block. Feels like a very slight amount below.

    Do you think I should use the Elring cutting ring gasket or use a thicker than stock MLS in this situation, given that I will be using the ARP head studs. I already have the cutting ring gasket and ARP studs kit.

    - - - Updated - - -

    Pistons are not above deck height on block. Feels like a very slight amount below.

    Do you think I should use the Elring cutting ring gasket or use a thicker than stock MLS in this situation, given that I will be using the ARP head studs. I already have the cutting ring gasket and ARP studs kit.

  13. #38
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    Quote Originally Posted by Vermont320i View Post
    Pistons are not above deck height on block. Feels like a very slight amount below.

    Do you think I should use the Elring cutting ring gasket or use a thicker than stock MLS in this situation, given that I will be using the ARP head studs. I already have the cutting ring gasket and ARP studs kit.

    - - - Updated - - -

    Pistons are not above deck height on block. Feels like a very slight amount below.

    Do you think I should use the Elring cutting ring gasket or use a thicker than stock MLS in this situation, given that I will be using the ARP head studs. I already have the cutting ring gasket and ARP studs kit.

    Yup if near stock pistons will be below deck. I think last measured a stock 1.8 Block here pistons installed in the shop it was .005" below deck.

    Whats the gasket difference compressed? Can simulate with a spreadsheet here just for a guesstimate. Assuming 10cc domed 1.8 pistons and .051 compressed stock gasket. Can compare with ballparking real close.

    Here's a guestimate stock M10B18 with .051 compressed stock gasket and assuming 10cc dome stock pistons.

    88 M3
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  14. #39
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    Assuming that less head depth equates to less gasket thickness (which may not be correct), using that calculator, 0.025” loss from head = 0.635mm off the deck = 0.665mm effective gasket thickness. (1.3mm-.635= .665). This raises CR to 9.49. I think... but acceptable limit for the head depth can be as little as 5.063”, which yields a 9.59 CR—-so does it matter enough to cause a future failure?

    If my assumption is correct about the correlation between head depth and gasket thickness, is it ignificant enough to need a thicker than standard gasket and/or MLS gasket?

    Looking at it a different way, what I have lost by having the head decked, .635mm off stock, actually is a decrease in the volume of the combustion chamber, which yields a decrease of 4 cc in that volume. This shows an increase in the calculated CR to 9.48..... way over thinking this, probably.
    Last edited by Vermont320i; 11-14-2020 at 06:20 PM.

  15. #40
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    Quote Originally Posted by Vermont320i View Post
    Assuming that less head depth equates to less gasket thickness (which may not be correct), using that calculator, 0.025” loss from head = 0.635mm off the deck = 0.665mm effective gasket thickness. (1.3mm-.635= .665). This raises CR to 9.49. I think... but acceptable limit for the head depth can be as little as 5.063”, which yields a 9.59 CR—-so does it matter enough to cause a future failure?

    If my assumption is correct about the correlation between head depth and gasket thickness, is it ignificant enough to need a thicker than standard gasket and/or MLS gasket?

    Looking at it a different way, what I have lost by having the head decked, .635mm off stock, actually is a decrease in the volume of the combustion chamber, which yields a decrease of 4 cc in that volume. This shows an increase in the calculated CR to 9.48..... way over thinking this, probably.
    Your not over thinking its correct about decreasing head chamber. My number on head cc's is just leftover from previous inputs. My head was measured in at 57cc chambers. Stock is suppose to be 63cc.

    Like I say looking at gasket thickness (actual feeler gauge torqued measured thickness) with calculator to see the actual figures and what happens; not significant enough change IMO, but i'm not a turbo guy and not sure what perceivable limit of 8psi is supposed to run on. Also what it's based on. There's lots of ways to reach the same compression ratio. Many probably ballpark of what others have done in the past. An engine that pays attention to "quench" IMO can make more with less. Meaning less detonation, less timing, more boost. It's probably the most overlooked detail that separates a good running engine from a great one. But dealing with factory parts and just machining surfaces to close up the quench gap increases compression to a high enough number detrimental to cross with a boosted setup using kjet etc.

    Quench is gasket thickness + piston deck clearance (adding to sheet to see on the fly)

    A build that gets the range into .030-.045" will have better results. But as I say can see how it can raise compression too high unless machine piston tops etc to compensate. Probably why a lot of guys go for flat tops in boost builds.
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  16. #41
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    No offense taken, I prefer claying so I can see the clearance and then measure it and then take into account the rest of factors, this runs parallel to additional methods.

    Randy
    Last edited by 320iAman; 11-15-2020 at 11:45 PM.

  17. #42
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    You fellas have way more experience than me, and really appreciate the technical information which is given and available here. I think I am going to put the Elring cutting ring gasket on with the Loc-title red gasket sealant and the ARP head studs, put it back together, and try it.

    I am also installing a wideband afm, boost gauge, blow off valve, and am looking for a correct warm up regulator, either a Volvo 240 turbo or similar.

  18. #43
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    Sounds good, break it in slowly-stay at 55 mph or so on highway and vary the speed for the first 500 miles and then change oil and filter.

    Randy

  19. #44
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    Got it. Thanks.

  20. #45
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    Update: got it back together with ARP head studs, Elring cutting ring head gasket, valves adjusted, distributor set, and timed with timing light (fancy one with the advance degrees—-pretty cool).

    Thanks for the advice, and also for the tips in the FAQ about setting the distributor. That had me scratching my head for a day or so. It all kind of clicked when I was double checking the valve clearances. I set them to .008 thinking they will tighten up a bit, but I will check that at 500 miles when I do oil, filter, and probably re-torque the head studs.

    Ran it about 10 miles easy, not going over 3500rpm or 50mph. Seems to run pretty well. Smoking a bit under throttle, could be burning off residual fluids in exhaust.

    Not declaring victory yet, but for tonight I feel pretty good. Malt power drink opened!

    Bill

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    fingers crossed!! keep up the good work!

  22. #47
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    Good to hear its up and running, remember your car speaks German so English words are huh ...

    Randy

  23. #48
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    Quote Originally Posted by Vermont320i View Post
    Update: got it back together with ARP head studs, Elring cutting ring head gasket, valves adjusted, distributor set, and timed with timing light (fancy one with the advance degrees—-pretty cool).

    Thanks for the advice, and also for the tips in the FAQ about setting the distributor. That had me scratching my head for a day or so. It all kind of clicked when I was double checking the valve clearances. I set them to .008 thinking they will tighten up a bit, but I will check that at 500 miles when I do oil, filter, and probably re-torque the head studs.

    Ran it about 10 miles easy, not going over 3500rpm or 50mph. Seems to run pretty well. Smoking a bit under throttle, could be burning off residual fluids in exhaust.

    Not declaring victory yet, but for tonight I feel pretty good. Malt power drink opened!

    Bill

    Good deal. Use that AFR gauge if installed. Tricky doing rolling road on your own and verifying with a gauge, but it's been done plenty of times. You'll notice the more hill ie load the more fuel to reach target afr's. Still mid 13's for midrange rpm power, and 13-12.5 (4500-7000rpm)@ WOT is a good target. Driveability wise you'll see afr's all over the place due to load and throttle position. Steady rpm and steady load should hit a desired number.

    I personally set valves to .003" cold (more on the cam) but some try to give flack for it. Been running it that way since well forever. But if not comfortable then stick with the book .007"
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  24. #49
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    Yes, the .008” valves are a little noisy, but I thought better than too tight. I’ve driven it about 100 miles now, taking it easy. Though I heard Sammy Hagar in my head at 55, Randy!

    It certainly needs some tweaking and this weekend I’ll try to get the AFM up and running.

    A recurrent issue is up and down idle and stalling when warm. A definite liability at stop lights, good thing there aren’t many here in Vermont.... other than general “vacuum issues”, any ideas on the warm idle? Like which specific vacuum leak points? I’ve replace all, I thought. Probably missed something. Any ideas would be appreciated.

    I will say that the drive ability of even this mild turbo makes this car so much better.

  25. #50
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    Idle seeking is due to the O2 sensor and is normal within 100 rpms or so, 1st thing that comes to mind is air fuel mixture- leaning on the fuel side-with a narrow band O2 sensor- 1 wire-start the car get it warmed up- pull the wire to the O2 sensor, using a multimeter set to low voltage- connect the red wire to the O2 sensor spade terminal and the black wire to ground( good place is between hood latch the hood rollers roll on to close)-- now keep the car at idle-look at the voltage reading it will settle down with a quality multimeter if the reading is below .5 volts--like .129,.135,.179 ect the air fuel mixture is too lean,, if the volts are above .5 like .9V its too rich, to correct lean condition turn the 3mm allen wrench very slightly clockwise-the adjuster for A/F mixure- this will increase base line fuel and reading will go up,, keep looking and slight adjusting the Volts till your around .5V-.7V, if the reading is .9V this is too rich--turn the 3mm allen wrench counter clockwise this will lower the Ve . 5V-.7V is good,, If the reading on the multimeter is stuck anywhere-that is wont fluctuate- you have a bad O2 sensor--I have been adjusting this way for years and years and it works quite well... generally wide variations in idle is due to gas side of the A/F mixture--vacuum leaks cause the idle to raise up and go high and steady... I hear the Dave Clark 5-Catch US if you can- not really food for thought. What your doing with the 3mm wrench is moving the piston that allows fuel to the fuel injectors in the fuel distributor to move up and down to correct too rich or lean air/fuel mixture-the result of which is too move up and down the CO % going to the catalytic converter. There are a couple more helpers to adjust a/f mixture, the Warm up Regulator and adjusting the jets or valves in the fuel distributor itself, been there with a slammed air fuel mixture and done the adjustments to balance it .Since your ramming more air into the air fuel mixture than stock--odds are good you'll have a lean A/F mixture and with that I close this arm chair analysis.

    Randy
    Last edited by 320iAman; 11-20-2020 at 11:19 PM.

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