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| Re: e16 crank |
Subject: Re: e16 crank
by jmac on 2011/11/25 12:55:17
I was a little bored, so I ended up typing a bigger reply than I originally planned. Here it is. As usual, I'm not perfect, and the stuff below is based on thoughts/opinions/ and experience, but it doesn't mean it's all 'the best' info or whatever. Read it on those terms please.
There's some good info on the darton sleeves page, but I'd 'maybe' add a couple of things. I haven't tried this specifically on a datto engine, but there are some issues that might crop up in general.
First - the sleeves are strong - I'm definitely not questioning that. BUT the more you take out of the block, the less there is remaining to help the threads where the head bolts attach - and any flexing there and the sleeve might be 'great' but the head gasket sealing might not be any more. And yes, you could run various types of o-rings and or custom gaskets, which will (generally) seal in the compression/combustion pressures in the cylinder - VERY VERY well, but often tend to seep coolant everywhere else (albeit usually fairly minor.
Even if the sleeve itself is very rigid, you can get side thrust to the point it tries to push the entire sleeve. Now I have to aay that they way they've designed them they sort of 'slot' together and would be pretty good, but you might find that it is necessary to also 'post' the block. what that involves is drilling and tapping the block outer walls, in the midde of each cylinder, on the major thrust face, then with specially machined bits of 'thread' (and opinions vary on what to make them out of) you then screw them in (with a flat/slightly radiusd tip) till they only _just_ barely touch the outer wall of the sleeve.Any further and they can crack, or distort the bore etc. This sort of thing has been done on honda b series engines when they go for larger bores (and occasionally longer strokes -which end up with considerable rod angularity and more side thrust.) It's also been done on older 'dinosaur' v8s (I've heard it was done on factory cleveland v8 blocks used in the early days of pro-stock. They had arguably borderline bore wall thickness - fine for 99.9% of uses, but when they started spinning them well in excess of 8000rpm, even in excess of 9, some people resorted to this extra step. I believe they also bored them out, then pressed in sleeves ('so called dry type') so that the bore wall thickness was the thickness of the sleeve, not that of however the block was cast.
I've never actually seen one done like that (this was US pro-stock stuff, and happened when I was an infant, so understandably it's not likely I'll ever see it in real life here in Aus!)
Although having the sleeve walls touching between each other does lead to more strength (if the block is cast like that it is called siamesed bores) some people argue it also means less consistent cooling around the entire cylinder. This would also tend to mean that as it heats up the expansion won't be 'round' it'll be more oval shaped. There are ways around that (including heating it all up to approximate engine running temps, and then doing the final hone). And there's more than a few race engines out there (chevy bow-tie blocks were siamese bore, also massively thick bore walls - could be bored over 0.125" oversize to a 400sb bore size, and I think some ford motorport blocks were too, but don't quote me on that). In contrast people seemed to have more issues with older chevy factory 400 blocks, with their siamese bores, but I think it might have been down to the fact they were a mass produced low-performance setup (the 400s as they left the factory, not a 400ci combo built from the bow-tie block or whatever) and so the 'production values' and controls were tailored to meet that much more modest set of criteria.
On the darton sleeves page, they mention a 'protective coating' on the outside of the sleeves, so the coolant/water doesn't corrode them too quickly. Based on what they discuss, it's probably just an application of phosphoric acide to the outside of the sleeves. This still is also marketed as 'de-oxidene' and a number of 'rust beater' or 'rust convertor' names. The stuff works. It isn't magical, but it does work. I'm not a chemistry guru, but I believe that what it does is effectively convert the surface layer of the metal into iron phosphate (or something along those lines). This is a (relatively) hard material, and is resistant to corrosion. If prepped and done right, it will end up forming a surface layer or barrier and help prevent oxidation of the metal underneath that surface. It's certainly better than nothing. I am curious as to where and how close to the top of the sleeves they apply it. In theory, this surface layer might end up changing the outide diameter of the sleeve (even if only microscopically). I'm sure they will have worked that one out, so I'm mainly saying it incase anyone else tried to diy their own sleeving. It probably wouldn't be enough to affect sealing/fitment, but I don't know for sure. This is a hobby where (in some situations, esp ultra high performance) less than half of one thousandth of an inch ( 0.0005") difference in size can be the difference between
success and failure.
Another thing I'd raise - if you go to a stroker crank, and one that you intend to rev high. The full counterweighted crank of this donor engine's crank is definitely a good thing.Yes, technically it is a little bit more mass, so it would have slightly less throttle response than if it only had counterweights like the a15 crank. BUT those extra counterweights smooth it out and should help keep the crank together at high rpm. If it was all out drag racing, where the motor didn't have to last more than maybe 10-12 minutes of full rpm full htrottle stuff between rebuilds then sure, go with the lighter option (even consider machining down the counterweights a little bit).
But for any engine where maximum engine life is a big deal - go the counterweights. Which leads to the next related thing - the front pulley. Most 4 cyl engines out there usually (or at least they used to) have just a 'pulley. No harmonic balancer (no crank dampener). It's not such a big issue on regular sized 4cyl engines, esp if the stroke isn't too long, and the revs aren't too high. But in a case like this - the longer the stroke, the more the crank can 'twist' end to end. It's not a huge twist, but it happens, on whatever level. SO again - whilst a smaller pulley will have less intertia, and have better throttle response, for longer crank life, what you really need is a proper dampener.
On the mini a-series engine, the 998s and 1275s have just a 'solid' pulley. On hte 1098, which actually has the longest stroke of all mini a-series engines (and smaller main bearing diameter, so more chance for crank flex) they had a 'proper' damper - a solid outer hub and solid inner one, and some sort of rubber inbetween the two. Much like the std balancers on holden 6s (the old red and blue 6s - which were basically a smaller engine, very similar in design, but no parts are actually interchangeable (afaik) as the chevy inline 6s (the ones with siamese intake ports and a head bolt running through the centre of the intake ports) and a bunch of other engines. I used to run the 1098 dampers on the 1275 engines I ran.
I don't know if there's anything off the shelf to suit it, but if there is, I'd definitely run one. If not, I'd look into finding one that fits some other engine (be it inline 6 or another 4, or whatever) and machining/adapting it to a 'big bore big stroke' custom crank engine. On Aus made hemi 6 engines (which have crank issues around 6100rpm - they are fine if you keep them above or below it, but sticking around that rpm point for extended period isn't a good option) there's a couple of aftermarket 'steel hub/rubber ' type balancers out there. But one guy went to the trouble of doing a production run of a custom hub/pulley - that would allow the fluidamper ( a fluid filled variant of the basic design) from a perkins diesel motor to be attached. Most of the 'traditional' 2 piece / rubber insert balancers work good, and tend to work best at one particular rpm range, and still pretty good elsewhere, but the fluid-filled style, they work very very well, and at practically any and all rpm ranges..
If I was trying to do a high revving hybrid crank a series engine - I'd definitely consider trying to adapt a fluid-damper style front pulley. But if that was too hard to achieve, at least I'd try for adapting a solid inner/outer hub with rubber insert type. When you start to add up the costs to do a stroker motor with this crank, well the $$s are considerable, so the extra cost of a good damper on the front is not really that much more expensive.
One of the signs of needing a better balancer at the front (though there can be other causes of this) is if you constantly find flywheel bolts coming loose, or worse still breaking/or the back of the crank snapping. It sounds 'crazy' that the 'damage' at the rear of the crank is caused by what is at the front of the crank (or what is 'not' at the front of the crank and needs to be put there!) but that's the way it goes.
I make no secret of the fact that I like boost - either turbo or supercharging - for the best value for money hp increase (and done right it can be achieved while still getting stock engine lifespan). That's all nice, but I have to say, I really admire the guys who push the limits of engines/development, but naturally aspirated (i.e. no turbo no blower, no nitrous etc). It takes time, money, massive effort, dedication, and behind the scenes, non stop testing and development - for example they might go through a bunch of engines, just finding the limits, and getting the most out of it.
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