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Yet Another 2.5L rebuild thread - engine in work

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  • Yet Another 2.5L rebuild thread - engine in work

    I've mentioned this rebuild a couple times on this forum, but I thought I'd start a official rebuild thread for documentation. Full disclosure - I am not an engine build specialist. I am a E30 M3 enthusiast. I've picked most of the parts and mods, but a local machine shop is doing the engine assembly (and a lot more) for me. This is going to be more of "here are the parts and mods" thread and not a "engine rebuild guide" thread. Check out a Jake or Xworks thread for how to. They are much more knowledgeable than I am. Hopefully this will be a decent "what are the end results of these particular mods" thread. This engine won't be unique, but I still hope that documenting it (adding one more data point to our rebuild database) will be helpful to the community.

    Let's start with what I started with. I got my M3 in March of 1999. I went through rebuild number one during the end of 2006/start of 2007. The upper oil pan was leaking badly which I used as an excuse to do some performance upgrades. Last engine build was:

    2.5L Evo Crank
    Stock Rods
    95mm CP pistons 11:1 CR
    292/284 Schrick Cams
    VAC "race" valve springs
    Stock rebuilt head by VAC, kept stock size valves and port.

    There were other small upgrades here and there but I don't want to bog down this thread even more. A couple years later I switched to Megasquirt engine management and ditched the AFM. I did the MS build, install, and tune myself.

    I started the current rebuild spring of 2011. The engine was running fine. It had a bit less than 20,000 miles on it since the last rebuild. This rebuild started because I wanted to have the head ported. Because of an oil pump failure about 1500 miles after the first rebuild http://www.s14.net/forums/showthread...light=oil+pump, I decided to have the bottom end disassembled and inspected.

    The local shop didn't find any indications of wear due to oil starvation. They did find that my pistons and cylinders were galled up. The previous engine builder undersized the cylinder bore. The current shop recommended new pistons. We might have been able to hone the cylinder, gotten bigger rings, and reused the pistons, but I decided to follow the shops advice and get new pistons. Here's a pic of the piston wear:

    old 2-5 piston wear

    So the new spec is:

    CP pistons 95.25 bore, 11:1 CR
    Hot street port by Mario at E-Ticket Motorsports, 30mm port 2mm oversized intake valve, and 1 mm oversized exhaust, supertech valves
    Carrillo Rods - I probably don't need them. I just was bitten by the "while I'm in there" bug
    292/284 Schrick cams from the previous rebuild
    2 piece Rally header
    48mm throttle bodies
    48mm evo venturi (I'll likely go with 18cm runner CF airbox eventually)
    Alpha-N via Megasquirt (same system as what I was running before)
    Add a knock sensors to work with the Megasquirt
    All of this is going into my old 2.3L block, unless someone has a source for an affordable sport evo block

    I highly recommend Mario at E-Ticket Motorsports. I'm happy with the head and he was very helpful.

    I just received the pistons today. Hopefully this rebuild will get back on schedule.

    Oh, I'll likely change to these one of these Hi-Z injectors http://www.diyautotune.com/catalog/f...s-c-52_58.html sometime after I get the engine running moderately well. I don't want to add an more headaches to my retune efforts, so I'll get the car up an running on my old injectors and a revision of my current tune.

    Now for some pics:

    head chamber

    Port2

    port3

    port4

    CP pistons

    Pistons bottom

  • #2
    Sexy pistons look sexy.

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    • #3
      Yea. Damn
      "Straights are for fast cars,turns are for fast drivers"

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      • #4
        Curious as to why the piston coat is only on the top of the piston. My mate runs a performance coating business and he always coats to the top of the first ring groove.....interesting.

        "But most of all...
        ... I like the way you move......"

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        • #5
          Looks like a nice setup... Gonna have to be moving a lot of air through those valves, head and exhaust
          Rich!

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          • #6
            I miss my pile of parts before my re-build. Keep us updated!

            elefantsupply.com

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            • #7
              Updates?

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              • #8
                Originally posted by Az in Oz View Post
                Curious as to why the piston coat is only on the top of the piston. My mate runs a performance coating business and he always coats to the top of the first ring groove.....interesting.
                Kind of an old comment but I wanted to mention something. AFAIK, the piston crown is not meant to touch the cylinder wall. It has a smaller diameter than the rest of the piston. I imagine not coating it all the way to the top helps to avoid uneven application in the ring grooves. I noticed this on some of my pistons. If the coating is not needed higher than the rings, then it may be a good idea to leave it alone.

                By the way, nice engine build Indie!

                Jake

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                • #9
                  No, unfortunately no real updates. A local machine/engine building shop is doing the build for me. They've been dragging their feet about getting the engine assembly going. Still, the rotating assembly came back from the balance shop before Thanksgiving. Hopefully the get going on it soon. My guess is that I'll have the car back in January or February.

                  Thanks for the encouragement Jake!

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                  • #10
                    Originally posted by indie_wannabe View Post
                    No, unfortunately no real updates. A local machine/engine building shop is doing the build for me. They've been dragging their feet about getting the engine assembly going. Still, the rotating assembly came back from the balance shop before Thanksgiving. Hopefully the get going on it soon. My guess is that I'll have the car back in January or February.

                    Thanks for the encouragement Jake!
                    That kind of stuff drives me crazy. So many projects take a completely f***ing ridiculous amount of time because we are dependent on people to do certain jobs for us, and they dick around, drag their feet, and do it when they feel like it. I am not the most patient person in the world, and being dependent on some slug's schedule drives me up the wall.

                    Fantastic looking build by the way....

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                    • #11
                      Well, I do finally have an update. Unfortunately it's not good. The machine shop just called and told me that the distance between the top of the block and the top of the piston is .073" (1.85 mm). I believe some call this distance pop-up. Isn't this about three times what it should be? Wouldn't I need a head gasket to be about .106" (2.7 mm) thick? Is this head gasket thickness acceptable?

                      I ordered CP pistons from VAC. Compression ratio target was 11.0. VAC speced the pistons based on block and head dimensions supplied by the machine shop. I've called VAC. After they review the piston spec, they are supposed to advise me on how to proceed.

                      I don't want to order new pistons, but I will if that's what it takes to make this build right. Unfortunately, I don't know enough to make a decision on my own. Advice is appreciated. I don't mind if the compression ration goes up some. I do have full control over fuel and spark, and I'm running 292/284 cams. Actually, I'd like compression to be higher, but I will be running pump gas. That's why I went with the 11.0 target. We won't know what the piston to valve clearances are until we have a head gasket. We won't have a head gasket until we figure out what to do about this higher than expected pop-up dimension......

                      Thanks,

                      Brad

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                      • #12
                        Brad, I'm intrigued with your build... Could you take a lateral view pic of the "pop up" I had a couple sets of JE pistons when I was building my current motor, faced with a similar dilemma, I had my machinist sonic test a piston, then cut the crowns flat to the ridge of the valve pocket (decreasing the CR) I hard anodized and ceramic coated the pistons as insurance.



                        I used a MLS gasket for my application it brought my compression where I needed it. Perhaps this can work for you, it took a fair amount of calculating and recalculating but it was a little cheaper than buying a new set of pistons and worked well for two years while I did my break-in.



                        Hopefully VAC can help resolve it though.

                        With 91 octane you really want to err on the safe side with a slightly lower compression than higher. I know you're aiming for 11+ but 10.5-11 with race gas works just as well, when you need it. But if you must run up near 12:1 CR, H2O/ Methanol injection is a perfect partner with a knock controller (knock controller, knock sense for MS).

                        I like CP, but I entrusted Steve at Top End Performance since he had a hand in the design of JE's S14 "deep valve pocket" pistons so I used TEP to bore the block to the pistons. Now JE has the job order on every piston so if you need to replace one or reference for future oversizing it's easy.

                        HTH
                        Last edited by ///schwartzman; 12-27-2011, 03:32 PM.
                        Rich!

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                        • #13
                          Schwartzman,

                          Thanks for the suggestions. VAC is working with me to resolve this issue. I don't want to go into details yet. Once everything is in working order, I'll update this thread. For now, I can say that VAC is being helpful and that I am satisfied with how things are progressing.

                          Would you still like pictures of the piston pop-up? I will try to take some next time I'm at the machine shop if I can get there before they disassemble the bottom end.

                          I was tempted to shoot for a little higher than 11 on my CR, but after some advice from other members, I'm sticking with 11:1. I will be running knock sense with my MS. I had been running 11:1 CR before this latest rebuild without any problems. I did have to retard timing a little in the midrange at part throttle, but that was it.

                          Brad

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                          • #14
                            No need if you've settled on a plan, unless you want to just keep it for reference. Good to hear VAC is helping you, sounds like the hard part is done. GL!
                            Rich!

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                            • #15
                              I finally have an update. The engine (with new and properly sized pistons) is mostly assembled. It shouldn't have taken this long, but at least it's almost done. Still need to put the oil pump an oil pans on. The oil pump shims arrived yesterday. After the bottom end is sealed up, it's time to put on the accessories. I think the engine will be going back into the car in about three weeks. Here's a pic of the progress so far:

                              Click image for larger version

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