GC9911 Posted 9March, 2018 Report Share Posted 9March, 2018 4 hours ago, Buchanan Automotive said: Porsche originally ( back in the mid 1980's ) list two oversize piston sizes for the 4.7L 928S , first over size & 2nd oversize Standard bore size = 97.00mm for the 4.7L 1st oversize = 97.50mm ( .25mm per material machined off the inside of cylinder in any one spot measured in relation to wall thickness ) 2nd oversize = 98.00 mm ( .50mm per material machined off inside of cylinder in any one spot measured in relation to wall thickness ) However the Porsche PET ( parts ) only lists the 1st oversize because almost no one ever purchased that size , 2nd oversize was the one that was needed for most bore wear over the decades & they are long been sold out So officially the answer to you're question = you're Cylinder Wall thickness ,then subtract .5mm = 1mm increase in the total bore size if bored to the 2nd oversize Bruce B Thank you Bruce, on behalf of all PFA peeps we are grateful for your contribution & consider ourselves lucky to have you on board. Troubleshooter 1 Quote Link to comment Share on other sites More sharing options...
Buchanan Automotive Posted 10March, 2018 Report Share Posted 10March, 2018 Hi Adam , to get to a 100mm bore size ( 5.0L 928S4 etc ) from the standard 97mm 4.7L bore size , here is a breakdown of what that means in bore/piston sizes } Standard = 97mm 1st oversize = 97.50mm 2nd oversize = 98.00 mm 3rd oversize =98.50mm ( first non Porsche not recommended custom size ) 4th oversize =99.00mm ( 2nd non Porsche not recommended custom size ) 5th oversize = 99.50mm ( 3rd non Porsche not recommended custom size ) 6th oversize = 100.00mm ( 4th non Porsche not recommended custom size ) I would be a bit concerned that the 97mm 4.7L alloy cylinder/s being bored out this much ( 6th theoretical oversize ) the thinner than recommended alloy cylinders would & could crack / fail later , if it was my own engine I still wouldn't do it & if it was a customers engine ( no way in the world ) Note } the 5.0L quad-cam engines , be it the 1986 M28 45/46 or the 928S4 engines & the 5.4L GTS engines had new / different ( to the 4.7L ) crankcases so the bores could be bigger with the correct thickness cylinders Regards Bruce Buchanan Quote Link to comment Share on other sites More sharing options...
ANF Posted 10March, 2018 Author Report Share Posted 10March, 2018 thanks Bruce, so looks like 98 is the max recomended Cheers Quote Link to comment Share on other sites More sharing options...
TINGY Posted 10March, 2018 Report Share Posted 10March, 2018 @ANF i found this on the bench at work for you Quote Link to comment Share on other sites More sharing options...
ANF Posted 10March, 2018 Author Report Share Posted 10March, 2018 5 minutes ago, TINGY944 said: @ANF i found this on the bench at work for you What would I want with a can of Pepsi I'm sure I could cram 2 of them in there, lumpy comes to mind.... Quote Link to comment Share on other sites More sharing options...
ANF Posted 4April, 2018 Author Report Share Posted 4April, 2018 I have been busily (well not really.... family life gets in the way, plus being without a car was a massive hassle!) pulling the engine apart and still hunting down info and parts..... I have now found some 98mm pistons and will pull the trigger on them once my machinist has confirmed bore size and that all is good on Friday (hopefully!!) I have also discovered that one car has slightly different heads.... one original and ope from an 85 model, subtle differences, I will Cc the heads and see where to go from there.... Engine looks much smaller now..... Corresponding piston to broken valve (no. 7) slight damage below top ring but not much else.... Quote Link to comment Share on other sites More sharing options...
ANF Posted 6April, 2018 Author Report Share Posted 6April, 2018 Well, I have more apart now, all pistons/ rods out, oh boy!! I think it may have been @Peter M who mentioned that no. 6 big end can have issues, well my no.6 and no. 2 are well and truly rooted!! Amazingly there was no bearing noise to be heard, I reckon both were close to failing! I am not sure but I would imagine that poor maintenance has contributed significantly to most of my current engine woes! A fair bit of sludge and even foreign materials in the sump!! The valve breaking most likely did a favour otherwise this engine may well have been toast! Thankfully crank bearings are not overly expensive! No. 6 rod, unfortunately no. 2 is worse!! Peter M 1 Quote Link to comment Share on other sites More sharing options...
3legs Posted 6April, 2018 Report Share Posted 6April, 2018 You're not giving me much confidence in my newly purchased 928 Adam. If it goes bang I will blame you Quote Link to comment Share on other sites More sharing options...
ANF Posted 6April, 2018 Author Report Share Posted 6April, 2018 Oh, did you expect to drive it as well...... On a serious note, ensure your engine (and everything else!) is maintained properly. And somehow if you are not sure of the service history, drop the sump clean it thoroughly and have a good look at things...... tazzieman, 3legs and Peter M 3 Quote Link to comment Share on other sites More sharing options...
944s2cab Posted 27May, 2018 Report Share Posted 27May, 2018 Wow, What a roller coaster of 928 ownership, Hows the head hunting going? Have you had you block fixed yet, Should be getting mine back on Wednesday Quote Link to comment Share on other sites More sharing options...
ANF Posted 28May, 2018 Author Report Share Posted 28May, 2018 On 4/6/2018 at 10:24 AM, ANF said: Oh, did you expect to drive it as well...... On a serious note, ensure your engine (and everything else!) is maintained properly. And somehow if you are not sure of the service history, drop the sump clean it thoroughly and have a good look at things...... Some highs and lows along the way.... Just waiting for some parts/ prices/ on some people now...….. Quote Link to comment Share on other sites More sharing options...
Gavn Posted 28May, 2018 Report Share Posted 28May, 2018 Great pics Adam....interesting to see the no2 & 6. The po of my car took the 4.7 out to 5.0 before it went bang so that matches with Bruce's thoughts on it being a stretch too far for that block. ANF 1 Quote Link to comment Share on other sites More sharing options...
ANF Posted 29May, 2018 Author Report Share Posted 29May, 2018 16 hours ago, Gavin (CliffToCoast) said: Great pics Adam....interesting to see the no2 & 6. The po of my car took the 4.7 out to 5.0 before it went bang so that matches with Bruce's thoughts on it being a stretch too far for that block. I had some trying to convince me that was the way to go Gavin, boring it out to 5.0 litre.... sounds good in theory! Then again I was quite happy with my 300 horses and it is still capable of crazy speeds. Hopefully a real update to this thread will be warranted soon...... 3legs and Gavn 2 Quote Link to comment Share on other sites More sharing options...
Gavn Posted 29May, 2018 Report Share Posted 29May, 2018 I think it can be done but there are certain blocks that are thicker (Japan?). No doubt the factory ones taken to 5.0 l are thick enough. When the one that's in my car went bang it was replaced with a thicker M......(can't remember) block....reputed to be better....time shall tell! The clover leaf/baffled style sump was also a feature....only available in certain years & helpful with oil starvation/frothing issues. Can't say I've done any long high lateral corners for it to matter yet....one day Quote Link to comment Share on other sites More sharing options...
ANF Posted 29May, 2018 Author Report Share Posted 29May, 2018 11 hours ago, Gavin (CliffToCoast) said: I think it can be done but there are certain blocks that are thicker (Japan?). No doubt the factory ones taken to 5.0 l are thick enough. When the one that's in my car went bang it was replaced with a thicker M......(can't remember) block....reputed to be better....time shall tell! The clover leaf/baffled style sump was also a feature....only available in certain years & helpful with oil starvation/frothing issues. Can't say I've done any long high lateral corners for it to matter yet....one day Yes, I have been told the same, almost a block by block situation, depending on variances/ etc. I think the 5.0 litre factory ones have a larger outside diameter on the cylinder to keep the wall thickness the same. Haven't you pushed the limits yet Gavin I did retrieve my heads yesterday and will start some work on them..... Quote Link to comment Share on other sites More sharing options...
Gavn Posted 31May, 2018 Report Share Posted 31May, 2018 On 5/30/2018 at 8:04 AM, ANF said: Yes, I have been told the same, almost a block by block situation, depending on variances/ etc. I think the 5.0 litre factory ones have a larger outside diameter on the cylinder to keep the wall thickness the same. Haven't you pushed the limits yet Gavin I did retrieve my heads yesterday and will start some work on them..... Oh I've pushed my limits on track but I'm coming to the realisation that the cars limits are much higher than my capabilities. Had a chat with the po on the phone the other day & he said after hundreds of laps at bathurst over a 10 year period he never felt like he got everything out of the car that was on offer & that his track spec cayman (which is why the 928 was let go) is still 2 seconds a lap slower than the 928.....so it seems I've got a way to go....a nice project to work on, getting more seat time & instruction. I think any aspirations I had towards a gtanything are on ice for some time (never mind relative running costs). Plus I like the bloodymindedness of taking a gt car & turning it into a track steed (I don't think I'd bother spending the time or money to do so but happy to play with the finished product). Cheers, Gavin ANF 1 Quote Link to comment Share on other sites More sharing options...
ANF Posted 31May, 2018 Author Report Share Posted 31May, 2018 2 hours ago, Gavin (CliffToCoast) said: Oh I've pushed my limits on track but I'm coming to the realisation that the cars limits are much higher than my capabilities. Had a chat with the po on the phone the other day & he said after hundreds of laps at bathurst over a 10 year period he never felt like he got everything out of the car that was on offer & that his track spec cayman (which is why the 928 was let go) is still 2 seconds a lap slower than the 928.....so it seems I've got a way to go....a nice project to work on, getting more seat time & instruction. I think any aspirations I had towards a gtanything are on ice for some time (never mind relative running costs). Plus I like the bloodymindedness of taking a gt car & turning it into a track steed (I don't think I'd bother spending the time or money to do so but happy to play with the finished product). Cheers, Gavin Good to hear Gavin. They do handle extremely well! Interesting about the Cayman, most would never have believed such a thing could happen! You may have already told me, but do you know how much your 928 weighs? All they really need to do is lose about 100 kg...… I like the "taking something not perceived as being quick" approach, although the 928 is plenty quick to start with All this 928 talk is wanting me to get mine fixed quickly... must track down all those pesky parts! Troubleshooter 1 Quote Link to comment Share on other sites More sharing options...
Gavn Posted 2June, 2018 Report Share Posted 2June, 2018 On 5/31/2018 at 10:15 PM, ANF said: Good to hear Gavin. They do handle extremely well! Interesting about the Cayman, most would never have believed such a thing could happen! You may have already told me, but do you know how much your 928 weighs? All they really need to do is lose about 100 kg...… I like the "taking something not perceived as being quick" approach, although the 928 is plenty quick to start with All this 928 talk is wanting me to get mine fixed quickly... must track down all those pesky parts! I think the time difference is down to the torque of the 5l compared with the cayman engine. Will look up the weight - it's a tin can so there's nothing in it...but the cage adds weight. ANF 1 Quote Link to comment Share on other sites More sharing options...
ANF Posted 16June, 2018 Author Report Share Posted 16June, 2018 First batch of parts have arrived Should be more next week and then more again after that..... Peter M, P-Kay, LeeM and 2 others 5 Quote Link to comment Share on other sites More sharing options...
ANF Posted 20June, 2018 Author Report Share Posted 20June, 2018 Second parts delivery!N.O.S. pistons, I only need one but these 4 were half the price of a one new one elsewhere.... 4 of my best existing ones will be used in conjunction with these Not sure if these are the right ones, to replace my "cooked" ones..... Peter M 1 Quote Link to comment Share on other sites More sharing options...
P-Kay Posted 20June, 2018 Report Share Posted 20June, 2018 liking that! Road to recovery....here we come ANF 1 Quote Link to comment Share on other sites More sharing options...
ANF Posted 20June, 2018 Author Report Share Posted 20June, 2018 8 minutes ago, P-Kay said: liking that! Road to recovery....here we come Thanks Peter! Hopefully be back out there tearing it up soon. A trip to machine shop to kick him into gear.... P-Kay 1 Quote Link to comment Share on other sites More sharing options...
944s2cab Posted 20June, 2018 Report Share Posted 20June, 2018 Looking good Adam, let the build begin ANF 1 Quote Link to comment Share on other sites More sharing options...
ANF Posted 20June, 2018 Author Report Share Posted 20June, 2018 6 minutes ago, 944s2cab said: Looking good Adam, let the build begin Thanks, you are doing a great job too! Quote Link to comment Share on other sites More sharing options...
ANF Posted 20June, 2018 Author Report Share Posted 20June, 2018 I also have a new timing belt and some good used hydraulic lifters for $20 each, these simple little lifters are about $500 each new!! Quote Link to comment Share on other sites More sharing options...
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