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Thread: 6G75 engine failures

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  1. #1

    6G75 engine failures

    Just an observation that most of the engine failures I have heard of or personally seen are due to main crankshaft bearing failures, NOT conrod bearings.

    We noticed that the main center bearing bolts stretch a full 15 thousandths of an inch over a 12 month/30 thousand mile period...way too much for the center main bearings.

    Then its engine failure.

    Solution is drop the sump and replace the bolts with heavier ARP bolts.

    Hope it help someone.

  2. #2
    Nice info man! I'm surprised I haven't heard of more 6g75 failure.


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  3. #3
    Red blower is correct on this it's the reason I had to have my 75 crank cut, only 77k on my motor..

  4. #4
    Senior TGC Member Isaurio's Avatar
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    ^^ yeah. For some reason the crank bearings where really scratch up. It was no reason for that since the DAM motor and head where MINT. I mean clean. Deez was already getting ARP for the RODS and Main bolts.

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  5. #5
    Even mitsubishi itself reported crank failures in their longevity testing. If you want to push that thing you need some good lower end work!

  6. #6
    So if I do this swap I need arp studs ect... ? Cuz I have been really planning to do this swap.also if one of u guys where going to do this swap what would u pick 74 or 75?and why?
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  7. #7
    TGC Regular foxbrand's Avatar
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    you can in fact just do the swap with either engine with no issues, redblower just noted this if you are planning running a supercharger with a none-MIVEC 6g75 swap, it is advisable to run ARP main bolts or studs at the very least in place of the factory hardware because the factory bolts stretch and cause a bearing failure, for peace of mind, replacing the main bolts with ARP main studs on the 6g74 (if you supercharge it), I would understand, but just due to the lower output of the 6g74, it isn't really needed as much

    as for engine swaps, both swapping in the 6g74 and 6g75 are both very advicable and completely fine, which you choose really comes down to how much more power and torque you want over the 6g72 (also using 6g72 cams in the 6g74 is also a very good upgrade in the swap) and how much your willing to spend

    a part list is detailed in the swap threads as while both engines can effectively be dropped in without modifications but you need additional parts to actually use either engine, in either engine swap, it is highly reccomended if not should be required to get your ECU reflashed after the swap is done

    which should you go with? Well, what size of a budget are you looking for? What are your power goals? How much down time can you afford with your car?

  8. #8
    The 75 stretches main bolts due to the long throw short rod nature of the rotating assembly. Piston switchback acceleration and peak piston velocities are significantly higher with the 75 that any other 6g7. This makes the crank want to twist and bend as well as increases the effects rotating harmonics have on it. Contrary to what people think part of what makes a forged crank strong is it's ability to deflect to a certain extent without breaking or losing certain geometry. While the 75 crank can take lots of pressure from the cylinders it is prone to flexing due to the outstanding geometry which puts excess stress on the main girdle and since Mitsubishi likes putting Chinese hardware in the 6g75 lower end the result is damaged components. Given fasteners that can handle the load and especially a good balance job the 75 takes abuse just fine. It is worth noting however that even those who push it's abilities aren't revving over 7500 even in mad built form without changing the geometry (basically unless Ray Pampina get's involved).

  9. #9
    thanks for the info and my power goal n/a wise is 250-275! i have been quoted 1300 for a 75 with 60k on it (a grade car-parts.com).also if i use my 72 cams do i need to send them out for refreashing or whatever?
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  10. #10
    TGC Regular foxbrand's Avatar
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    the stock 6g75 cams are much better than the stock 6g72 cams so you shouldn't be swapping them in

    however, if you send out the 6g75 cams out for anything, you could send them to Delta Cams to be hardwelded and reground with more agressive intake and exhaust profiles, if you replicated the MIVEC high speed profile on the intake and then replicate the exhaust profile, with an intake, exhaust, headers, a host of other bolt ons and tune, you should approach the 300 whp mark, likewise if you are planning a 6g74 swap, using the 6g72 cams is one option, however if you also get the cams reground, it is also highly benifitcial

    speaking of the 6g75 MIVEC cams, the duration for the intake high speed is 264 (opens 15 degrees before top dead center and 69 degrees after bottom dead center and the duration for the exhaust is 256 (57 degrees before bottom dead center and 19 degrees after top dead center), I'm not entirely sure on what the respective lift is, if anyone could post that, it would be save me some digging
    Last edited by foxbrand; 01-04-2013 at 11:56 AM

  11. #11
    So is it advisable that an I/H/E swapped 75 should have its crank and related hardware upgraded?
    Its Not How Fast You Go But How Well You Go Fast

  12. #12
    Advisable, yes. Necessary, probably not. I've had my 6G75 in my car for roughly 3 and a half years now with no issue. It's not lightly driven at all either. It has withstood constant abuse since the day it was swapped. Still running strong.
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  13. #13
    Quote Originally Posted by M-Rod View Post
    Advisable, yes. Necessary, probably not. I've had my 6G75 in my car for roughly 3 and a half years now with no issue. It's not lightly driven at all either. It has withstood constant abuse since the day it was swapped. Still running strong.
    I had intended to just ask you if you did yours? But I didnt want you to feel like I was hassling you with one question after the other lol.
    Its Not How Fast You Go But How Well You Go Fast

  14. #14
    Mine spun bearings in 250 miles post fresh rebuild with ARP and a balance job. It all depends, if I were to do it again I'd just get the lowest mileage engine I could and not worry about it.

  15. #15
    Thats what i'm going to aim around 30k miles or less, I havent seem anything with extremely low mileage
    Its Not How Fast You Go But How Well You Go Fast

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