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Discussion Starter #1
Greetings all,

I've lurked for quite a while on this forum while never seeing a need to dive in a do much other than check out all the great information available here. Well, I'm in deep with my ride and have been for some time. June of 2012 I was headed home on the freeway and dropped from 5th to 4th for some spirited driving. It never redlined and when I upshifted at about 6600 RPM, the engine suddenly lugged and a bunch of black smoke started spewing from the exhaust (as was visible in my rearview).

After a day of non invasive diagnostics I came to the conclusion that the #3 cylinder had lost all compression and that I would need to tear into it in order to fully assess the damage. Now, I work for the railroad and don't have a lot of free time to take something like this on, hence the year plus this has been sitting. Lately, I have had the spare hours to spend and have gotten back into sorting this problem out. Here's what I found:


Number 3 Cylinder


Number 2 Cylinder

Here's the vehicle backstory that I find a little informative. I'm the third owner of this car that originally was purchased new in Palm Springs, CA. I don't think that owner took great care of the car as there was a lot of heat damage to the interior (warped plastics, dash in poor shape, etc). The second owner was a dealership near Glendale that did a "refresh" under the hood that included rebuilding the fuel injectors. I've found a bunch of things that just don't look right (hose, wire routing, oil/coolant leaks, etc) that just point to the car being poorly taken care of.

I intend to do a full rebuild (meaning complete disassembly followed by new pistons and rings, bearings, a few tweaks for reliability) and was wondering who do you recommend for pistons? I've looked at Wiseco and VAC and it seems they are the only shows in town. If anyone has experience with them, or others, as well as anything I should be watching out for I'm all ears.

Thanks in advance!
 

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Wow, I don't think I can contribute much except to wish you luck with the project. I saw more of the this view of my own engine than I wanted recently, with head gasket/valve replacement/timing components done (not by me).

Forgive the ignorance, but how does that happen to a piston? It seems strange for the damage to be in several spots on the edge. Is the top of the bore damaged also? It seems so in the pics, but hard to tell. Can that be repaired, if so?

It will be interesting to see what the others look like, eh? Hope to see more pics.
 

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Discussion Starter #3
Well, most damage like this is usually due to fuel mixture. Too lean (that's why I think the rebuilt fuel injectors are suspect) results in higher temperatures in the combustion chamber. The part that's burnt, on both pistons, is on the exhaust side. Burnt pistons, sadly, cannot be repaired. You toss them and start over. There is scoring towards the top of the cylinder, which has me concerned about whether or not just honing the bore will suffice as a repair or will I need to go for an overbore. Either way I'm replacing all the pistons but I'd prefer not to punch it out and keep the stock displacement.

I'm planning on documenting the rebuild and sharing with any that get stuck in a similar situation. I've worked on more than a few small block Chevys and so far this hasn't been too different (other than a lot more wiring). Thanks for taking a look and offering what you could.
 

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Hi, if you want to keep the stock size pistons you could have the faulty cylinders sleeved. I had this done on one cylinder on my B10 engine and it worked a treat.
 

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Are those custom? Do you mind disclosing how much you paid? I visited the website but they look like a domestic focused manufacturer, but I take it they'll make whatever you want. How many miles have you put on your M5 since the rebuild and did you stick with the stock CR, or did you bump it up?

My apologies for the slew of questions but I'm looking at all my options. Thanks for the information either way!
 

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We carried out a full rebuild based on our requirements .

I'd suggest that you call the company and discuss the possibilities with them .

Best wishes ,
D
 

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Discussion Starter #8
Update for any that are interested. I'm getting the machine work done through the machinist that works with Avus Motorsports in Glendale, CA. Mark Degraff, the owner, was extremely helpful over the phone and the pricing was very in line with what I expected for the procedures I need. I will be punching it out, probably to a full 1mm over and getting the cylinder head reconditioned through their services as well. VAC motorsports is the top candidate for supplying the pistons/rings as it is an off the shelf item at there end and not a special order product (with the associated return issues if there's a problem).

A question to any out there in the know (because I'm not); do you have a formula for HP calculation based on CR? I'm looking at the stock 10.5:1 vs 11:1 and wondered what gains I would see and if any other components would need to get upgraded to accommodate the increase.
 

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Might be a bit risky pushing the CR, especially given the issue you've had. There's no knock sensor, and if you get anything but high grade fuel you could risk detonation.
 

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As advised above I'd stick to stock compression, 10.5 is upped compression aswell, stock is 10.0 as far as I'm aware.

I'm rebuilding a S38B36 as well, bought it as a parts lot which has bees disassembled for 7 years. Looks like I need new pistons as they're on the upper limit.

So I would like to ask some questions as I'm having trouble completing the order form, I can't determine the compressed headgasket thickness, gasket bore diameter (I suspect this is in installed position?). Valve angle seems difficult to determine and is it wise to go with offset pins?

Thanks,
Angelo
 

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Discussion Starter #12
@DevilTJE, I couldn't find the head gasket specs you're looking for, I assume you're going beyond stock but do have access to the valve train spec sheet:

<a href="http://s1271.photobucket.com/user/Gumwars/media/S38B36/ValveSpecs_zpsc868c976.png.html" target="_blank"><img src="http://i1271.photobucket.com/albums/jj635/Gumwars/S38B36/ValveSpecs_zpsc868c976.png" border="0" alt=" photo ValveSpecs_zpsc868c976.png"/></a>

Hope that helps.
 

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Yep already got that info, but thanks none the less.
I'll be picking up a new head gasket today so I'll be able to measure if 1,74 mm that's mentioned via various sources is in installed or uninstalled condition. Still have to do some more searching on my other questions.
 

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Discussion Starter #14
VAC is going to be my supplier for pistons, rings, and bearings. I'll post a price/parts list when I get more time for anyone looking to do the same. The cost, shipped, is going to be around $1600, if anyone is interested. My only concern is sorting out the CR, as I'm not interested in blowing up my motor for marginal performance gains. Looks like stock is going to be a custom job!
 

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Have you asked VAC what they advice for a stock build regarding the CR? Good luck with your build .

For future reference I just measured the new gasket thickness it's just over 2mm, so my guess is that E 1,74 mm is in compressed condition.
 

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Discussion Starter #16
Thanks for the head gasket measurement. I spoke with Steve at VAC and the stock CR will be a custom job. The cost is minimal ($49 more, not per piston thankfully) but does put it into the realm of being hard to return. For all the higher CRs, they recommend camshafts, cam gears, and chips to compliment them. I'll stick with stock.
 

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To those concerned:::::

As i can speak of own experience,, but B38 rebuild

I would stick with oem cr,,, its enough and more compression would need remap etc etc,,

there a bunch of producers that can supply ,,what ever you want.......... CP WISECO JE DIAMONDS bla bla ....... the cost is more than 50% less vs oem pistons,, and i thin i can speak generally for all of us that have ordered this stuff,,,,,, the quality is outstanding,, and forged

if you havent opened your engine ,, you can have a look of mine,, if you want,, most parts are similair,, heads,, camshaft,, chain,, sump, airbox,, headers etc etc

alpina.123.is : S38B38 Engine rebuild | 31.08.2013

but the B36 do NOT have oilcooled pistons,,,,,, why not.. is an extremly strange decision that the engineers at BMW made back in the days
 

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Thanks for the head gasket measurement. I spoke with Steve at VAC and the stock CR will be a custom job. The cost is minimal ($49 more, not per piston thankfully) but does put it into the realm of being hard to return. For all the higher CRs, they recommend camshafts, cam gears, and chips to compliment them. I'll stick with stock.
So I am currently mid-rebuild, and also purchased CP pistons from VAC. However, when I spoke with Brian from VAC, he assured me the 10.5:1 compression would not require any tuning/cams/etc. Can anyone verify one way or another? Over here in NC+VA, premium is widely available as 93 octane...

I think my car is currently running a chip, but previous owner didn't know which one. If it isn't safe to run the 10.5 vs the 10:1, is there something I can do besides cams to make up for it?
 

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So I am currently mid-rebuild, and also purchased CP pistons from VAC. However, when I spoke with Brian from VAC, he assured me the 10.5:1 compression would not require any tuning/cams/etc. Can anyone verify one way or another? Over here in NC+VA, premium is widely available as 93 octane...

I think my car is currently running a chip, but previous owner didn't know which one. If it isn't safe to run the 10.5 vs the 10:1, is there something I can do besides cams to make up for it?
You'll be fine at 10.5:1 with that fuel
 
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