kiwipetrolhead 1 Report post Posted October 12, 2006 Hi there, The Engine Builder is taking along time to finish my '83 E21 323 engine rebuild, but he's nearly there. However, this morning he phoned to tell me the pistons protrude above the top of the block by 20 thou. He re-surfaced the block but he says he only took 5 thou off, which means there must have been a 15 thou protrusion before. Does that sound right? I took the pistons out myself and don't recall any protrusion, not that I took any notice, but 20 thou seems like a lot to me - and he must be a bit concerned too given that he phoned me about it. He said the head gasket is really thick though and he thinks it will be OK, but that is just a guess on his part (his admission). But if that's how these engines are and he was to take 20 thou off the top of the pistons then the compression ratio is going to be low and the engine would be a slug then. Any ideas? Is this amount of protrusion normal or do I have a problem? Thanks Paul Quote Share this post Link to post Share on other sites
Gus 5 Report post Posted October 13, 2006 got any pics? Quote Share this post Link to post Share on other sites
kiwipetrolhead 1 Report post Posted October 13, 2006 got any pics? No, and I'm not driving all the way over to take some... too far to go just for that (P.Nth - Feilding). Once I pick the block up though I can take some pics, but that won't be until after it is too late, when it's all assembled. I'm hoping to pick it up in the morning. P Quote Share this post Link to post Share on other sites
kiwipetrolhead 1 Report post Posted October 17, 2006 Hi Gus, I finally got my engine back this afternoon. I'll try to get a photo done sometime this week. But the engine builder said he spoke to the BMW dealership and they said the top of the pistons should be flush with the block on TDC, so he is still a bit concerned. He has asked around a lot about this one and has got conflicting answers, so I don't know. Perhaps I should ditch this car a get something a bit newer - one where there is more knowledge floating around. But it is a nice car and in good nick. I am quite attached to it... after 7 years of ownership so far. Cheers Paul Quote Share this post Link to post Share on other sites
mops 4 Report post Posted October 17, 2006 what engine is it ? what does bentley manual says ? remember bmw uses different cylinders on same engines.. like m20b25 sported 2 different types of pistons m20b27 3 different types, and these are interchangable (even with m50 pistons...) if all else fails, 15 thou is bloody not much... worst thing is that you will have some exrea compression. just make sure (by turning engine over once head is on carefully with a hand) that pistons have *some clearance* with valves... remember rods streth at high rpm's up to 0.5mm (probably not that much in that engine), but as long as you got clearance, you will have no problems... Quote Share this post Link to post Share on other sites
kiwipetrolhead 1 Report post Posted November 7, 2006 what engine is it ? what does bentley manual says ? remember bmw uses different cylinders on same engines.. like m20b25 sported 2 different types of pistons m20b27 3 different types, and these are interchangable (even with m50 pistons...) if all else fails, 15 thou is bloody not much... worst thing is that you will have some exrea compression. just make sure (by turning engine over once head is on carefully with a hand) that pistons have *some clearance* with valves... remember rods streth at high rpm's up to 0.5mm (probably not that much in that engine), but as long as you got clearance, you will have no problems... It's 20-thou now (after the top of the block was skimmed), but yes, it should be OK - the head gasket is thick enough I think. I have the head back on now, but not yet timed it up and turned over. I can get a thicker head gasket for $100 if there is a problem. But it's not just valves that could hit, too much piston protrusion would mean the pistons would hit the head in the squish area, but the head gasket is thick enough that that shouldn't be a problem. BTW, it's an M20 engine and it's a re-ring job, so the original pistons are being used. Also, what's "bently manual"? Cheers Paul Quote Share this post Link to post Share on other sites
mops 4 Report post Posted November 13, 2006 It's 20-thou now (after the top of the block was skimmed), but yes, it should be OK - the head gasket is thick enough I think. I have the head back on now, but not yet timed it up and turned over. I can get a thicker head gasket for $100 if there is a problem. But it's not just valves that could hit, too much piston protrusion would mean the pistons would hit the head in the squish area, but the head gasket is thick enough that that shouldn't be a problem. BTW, it's an M20 engine and it's a re-ring job, so the original pistons are being used. Also, what's "bently manual"? Cheers Paul bentley e30 manual. it's like hayness (series) manual, but SO MUCH BETTER !!! it has very detailed procedures and pics and schematics and wiring diagrams. Just got my own recently... this thing has even gearbox rebuild guide with pics !!!! P.S. i'm trying to find out whether m21 diesel HG will go in instead of m20 petrol HG... surly diesel one must be higher rated... Quote Share this post Link to post Share on other sites
