Mike H Posted July 21, 2006 Posted July 21, 2006 My engine is a 42D from 1992. The tip about the pistons was from my machine shop. He's a guy that builds vintage racing Aston Martin engines and Formula Ford Zetecs so I guess he knew what he was on about. One time when I went in he was resleeving a V12 Ferrari engine. As he put it replacement pistons are mass produced and there could be a thou' or so difference between each one. When the piston clearance in the bore is only 2 thou' it makes a big difference. Good luck on the rebuild. Mine turned into a bit of a 'mare because you can't get +020 pistons for a 4.2!! I used +020 low comp pistons from a 3.9 and had the top and skirt machined. In the end I now have a high comp (9.95:1) 4.3ltr rather than a low comp (8.95:1) 4.2ltr. Get your deck heights checked too, mine were different side to side by about 15 thou' !!! Oh and you probably know this - get it pressure tested for water leaks while you're at it. All the best, time to go home. Mike Quote
adamnreeves Posted July 21, 2006 Author Posted July 21, 2006 My engine is a 42D from 1992. The tip about the pistons was from my machine shop. He's a guy that builds vintage racing Aston Martin engines and Formula Ford Zetecs so I guess he knew what he was on about. One time when I went in he was resleeving a V12 Ferrari engine. As he put it replacement pistons are mass produced and there could be a thou' or so difference between each one. When the piston clearance in the bore is only 2 thou' it makes a big difference. Good luck on the rebuild. Mine turned into a bit of a 'mare because you can't get +020 pistons for a 4.2!! I used +020 low comp pistons from a 3.9 and had the top and skirt machined. In the end I now have a high comp (9.95:1) 4.3ltr rather than a low comp (8.95:1) 4.2ltr. Get your deck heights checked too, mine were different side to side by about 15 thou' !!! Oh and you probably know this - get it pressure tested for water leaks while you're at it. All the best, time to go home. Mike 42D from 1992, that a good find. Is that an interim block or is it X-bolted. 15thou deck to deck, christ! I was intending on sending the block and heads somewhere (do not know where yet) to clean, pressure check, rebore, hone, check tolerances and now check the decks! Quote
adamnreeves Posted July 23, 2006 Author Posted July 23, 2006 I thought honing was done to aid oil retention in the bores, not *just* to run in the rings. According to this on the Mahle web site honing is for making sure oil hangs around to do it's job. With that vital function in mind, are you sure Rover V8's weren't honed in the 80's? I find that statement staggering if it's true, and shows just how outdated the engineering practices were at Rover in the 80's. Yep, I was aware that the honing marks would mean that oil adheres to the bore more readily, and I have read this cited elsewhere also but I thought this was an advantageous side effect of honing but the main reason for honing was to bed the rings in more efficiently resulting in a better seal between the rings and the bore. BTW, now that I have my pistons removed from their bores I can see a honing pattern in the bores so I guess rover did hone the pistons at this time. Yes, yes, when this posting is done, I shall post topics like this in the tecbie section. Quote
Mike H Posted July 24, 2006 Posted July 24, 2006 42D from 1992, that a good find. Is that an interim block or is it X-bolted. 15thou deck to deck, christ! I was intending on sending the block and heads somewhere (do not know where yet) to clean, pressure check, rebore, hone, check tolerances and now check the decks! Neither, it's just the same as the old 3.9 block I'm afraid but with the longer stroke crank. I think the difference was about 15 thou. I asked the machine shop guy to cc the bores after trial fitting one of my modified pistons so I could work out the compression. He cc'd a couple from each bank which is how he spotted the difference in deck height. Mike Quote
Martin Keene Posted July 24, 2006 Posted July 24, 2006 With that vital function in mind, are you sure Rover V8's weren't honed in the 80's? I find that statement staggering if it's true, and shows just how outdated the engineering practices were at Rover in the 80's. Having seen the V8 line before it was removed, I'd be surprised if they weren't honing. The machine looked more like something from the 1880's rather than the 1980's... Shagged was not the word. Quote
adamnreeves Posted July 24, 2006 Author Posted July 24, 2006 42D from 1992, that a good find. Is that an interim block or is it X-bolted. 15thou deck to deck, christ! I was intending on sending the block and heads somewhere (do not know where yet) to clean, pressure check, rebore, hone, check tolerances and now check the decks! Neither, it's just the same as the old 3.9 block I'm afraid but with the longer stroke crank. I think the difference was about 15 thou. I asked the machine shop guy to cc the bores after trial fitting one of my modified pistons so I could work out the compression. He cc'd a couple from each bank which is how he spotted the difference in deck height. Mike When checking the deck heights did they check that they were a true 90degrees to the crank? Quote
Mike H Posted July 24, 2006 Posted July 24, 2006 Yes I believe so. I think it's best you find somewhere that is familiar with V engines as they should have some kind of jig for mounting the block that enables it to be rotated correctly when machining. Mike Quote
adamnreeves Posted July 24, 2006 Author Posted July 24, 2006 Yes I believe so. I think it's best you find somewhere that is familiar with V engines as they should have some kind of jig for mounting the block that enables it to be rotated correctly when machining. Mike Oh, I tell you what I am confused where I should get my work done. Reading all about JE, DJE, RPI on their respective websites, they make statements that you should send stuff to them as they know what they are doing, the subliminal message being that engine builders that do not specialise in Rover V8 are not to be trusted! well that is how I read it anyway. I do not have enough experience to know if this is just marketing hype or they make a valid point. I was wondering if these V8 specialists are a lot more expensive than say the general engine builders/engineers. Quote
Thrustyjust Posted July 24, 2006 Posted July 24, 2006 Anybody can build a V8,but a lot don't make as much horsepower as they claim.The specialists know how to do it.It may be false economy and a bit of a bummer,if you put a load of money in and don't reap the rewards,as you seem to think you'll get in terms of horsepower. Quote
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