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| Rebuilding Engine, Pocketing Block https://ausmini.com/forums/viewtopic.php?f=5&t=9605 |
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| Author: | Anto [ Fri Jul 29, 2005 6:26 pm ] |
| Post subject: | Rebuilding Engine, Pocketing Block |
Hi Guys, Just want to throw round some ideas and get some input. My car currently needs a new motor as I melted a hole in the last one. I have a 1275 sitting round here waiting to be rebuilt, but I want to do it properly - starting with a rebuilt gearbox. So in the interim I thought I might throw something else together. I have access to a stripped 998 motor, 20 thou over flat top pistons. From memory in quite good condition I believe you could still see honing marks. I was thinking about reassembling it with new rings and bearings, but without machining the crank (it is in quite reasonable condition). Alternatively my old engine needs the block replaced but otherwise it has 20 thou over dished Hepolites, and I was thinking I could bore out my spare 998 block to take these pistons and the 1098 crank, and replace the bearings (assuming the crank is still good, I haven't pulled it apart yet). The main problem is the cylinder head - I melted a big hole in my 12G202, and my spare 998 heads are all pretty bad. I do however have a good 12G940, rebuild, ported, double valve springs. How hard/expensive is it to pocket the block for this head? And, will it work with the flat top pistons, or will I have problems with the compression ratio? Any thoughts? Remember the idea was to make this motor relatively cheap, and not have it in the car for that long. It will have a slightly uprated cam and duplex chain, fresh Cooper S clutch etc, but otherwise be a pretty tame motor. Cheers, Anto. |
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| Author: | fuzzy-hair-man [ Fri Jul 29, 2005 6:30 pm ] |
| Post subject: | |
This might help http://www.ausmini.com/forums/viewtopic.php?t=9141 |
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| Author: | Zizzle [ Fri Jul 29, 2005 8:12 pm ] |
| Post subject: | |
So how did you melt the thing? |
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| Author: | drmini in aust [ Fri Jul 29, 2005 11:19 pm ] |
| Post subject: | |
Anto it's not hard to pocket the block. Details are in Hammill's book `How to Power Tune the BMC/BL/Rover 998 engine'. $39.95 at www.pitstop.net.au Or send me an email and I'll give you some hi-res pics of the relevant pages... 
You will need to increase chamber volume, as stock 1275 head is only 21.4cc. A 202 is 26.1 and a 295 is 28.3. When you want to reduce it again for the 1275 motor, just deck the head. 
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| Author: | 9YaTaH [ Fri Jul 29, 2005 11:32 pm ] |
| Post subject: | Easy.... |
Zizzle wrote: So how did you melt the thing?
Easy....coming along the highway with me saying just a little further, just stroke it along, stop and check the plugs, clean the plugs, see how far you get now, watch the temp guage, keep the revs up, don't let it lug....on and on I went....and on and on went Anto 
Anto made some good progress in between the stops waiting for the thing to cool down.... the thing had blown a head gasket...but it was still chaff cutting along on three... then finally it went phutt..like an air compressor relief valve and took a chunk out of the combustion chamber.... |
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| Author: | Lillee [ Sat Jul 30, 2005 12:13 am ] |
| Post subject: | |
Ouch! Sounds nasty! Can I ask why you didn't call for a tow? or is that adding salt to the wound? 
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| Author: | Christoph [ Sat Jul 30, 2005 11:10 pm ] |
| Post subject: | |
Dont ask me... it got towed in the end anyway... oh well. The head has a nice channel melted out of it along with the block between 3rd and 4th cylinders. I thought it only happened on alloy heads! |
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| Author: | drmini in aust [ Sun Jul 31, 2005 8:17 am ] |
| Post subject: | |
I've seen that happen on Mini 1275 race heads between cyls 2-3. And welding it (even TIG) doesn't often work as it's between 2 exhausts. On a smallbore head you might get away with welding it- between 3-4 it's next to the inlet valves. But unless it's a 295 or a highly modified 202 head, I'd just bin it and find another. Plenty of 12G202 or 12A1456 heads about.
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| Author: | 9YaTaH [ Sun Jul 31, 2005 11:27 am ] |
| Post subject: | Ummmm Deeerrrrrr |
68Delux wrote: Ouch! Sounds nasty! Can I ask why you didn't call for a tow? or is that adding salt to the wound?
A very good point you make there..... but with Canberra/Murrambateman and a friendly house to leave the thing at to whip the head off and fit a new gasket only about 30 clicks away and it getting late in the arvo and Anto not with a roadside service plan.....weeeeeelll... well....it seemed like a good idea to me at the time 
I thought as long as we switch it off as soon as the temp begins to rise then wait for it to cool....we might get away with it.....dumb really when you don't know how bad the head gasket has failed....if only Anto had had that spare gasket he usually carries...might have been a different outcome (I have got away with doing something similar in a 6 cylinder holden in the past...no excuse though  )
I have already publicly apologised to Anto....hey, but a little salt may prevent it ever happening again... 
I was trying to help till the end....Antos mobile battery was flat so we used mine to call his brother about 4pm or so....by the time we arranged a trailer it was dark...and the turnoff was unlit...so I went say ten clicks towards Canberra to wait on the side of the road for the rescue vehicle. I stayed with the Ant man in the dark until his friends turned up with the trailer...helped load then got away about 7pm. Just another day on the side of the highway of life.... 
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| Author: | Anto [ Mon Aug 01, 2005 10:49 am ] |
| Post subject: | |
Yes well its no big deal the engine needed rebuilding anyway, it consumed a couple of litres of oil on the trip to Albury and back
Kev are you sure I'll need to enlarge the chambers for compression? The flat top 998 had a slight score on one of the bores so I'm not going to use that. Instead I'm going to take my 1098 internals (20 thou dished Hepolites) and put them in a 998 block I have that hasn't been bored yet. My 1098, when disassembled, was in pretty good condition, makes me wonder why it burnt so much oil. Maybe it was just the head. When I was looking up CRs I found various reports from 9.5:1 upwards, for a stock 12G940 on a standard dished 1098. However, my head may have been decked in the past! |
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| Author: | drmini in aust [ Mon Aug 01, 2005 7:16 pm ] |
| Post subject: | |
Anto, is it a 998 or 1098? You need to do the sums.. read your Vizard book.
A 1220 motor (bored 1098) I built a while back using 68mm flat top Imp pistons, and a 29cc 12G295 head, was 9.57:1. To check if head has been decked measure the thickness. They were usually 2.750" thick when new. |
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