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The crank has a longer than standard throw, i.e. it moves the piston in and out more, and so the engine has more capacity.
 

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Discussion Starter · #3 ·
thanks
so the case as to be machined for it to fit?
it can be used with standard pistons,barrels and heads?
 

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hermione_beetle said:
thanks
so the case as to be machined for it to fit?

Depends on length of stroke, but yes, they usually need some clearancing, to stop bits hitting each other. ;)

it can be used with standard pistons,barrels and heads?

Again, depends on the length of stroke, but since the aim of a stroker crank is to increase the capacity beyond what can be achieved by changing barrels & pistons alone, sticking with stock B&P's would be a bit pointless :D
Cheers
 

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I'm currently looking into the possiblilities of building an engine with a stroker crank for my Bay. I'm more concerned with low-down torque, reliability and economy rather than maximum speed and RPM.

So the current plan is as follows (subject to change at any point!):

78mm stroker crank
Uni-tech rods (they're clearanced around the big end for the larger crank)
40mm inlet valves
35mm exhaust valves
85.5mm barrels and pistons (i.e. stock 1600cc)

With the extra stroke on the crank this will actually put the displacement up to 1791cc. As I'm using the uni-tech con rods with the 78mm crank and also retaining 85.5mm barrels and pistons the case requires zero clearancing. Not that I was bothered about having to have the case machined (it is getting full flowed anyway) but it also keeps the engine budget a bit lower and I could always upgrade to 90.5mm barrels and pistons at a later date if needs be.

I'm also using stock heads but machined to take the bigger valves.
 

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it's a shame they don't do stroker height pin (B) pistons in 85.5mm, as that'd make life a whole lot easier. I built a very similar engine for a friend a few years back, but it wasn't as simple as we'd hoped (working on past experience with 'B' pistons and low CR). We neded up with thick spacers each side, which meant the tinware didn't fit properly and needed loads of fettling to sort, and there was a lot of clearancing to do on the piston skirts etc, as they weren't designed to move so far down the bore. In hindsight, we'd have saved a whole lot of time and effort by stepping up to 90.5s. Not only will the 2165cc motor offer more power, the CR on a normal case will usually work out somewhere around ideal for your needs (assuming the case hasn't been milled on the faces), and the pistons will most likely bolt right on.
Like I say, it's not impossible to do, but I'd rather step up the power, reduce the labour and have a stock-width motor with tight fitting tin every time!
 

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Discussion Starter · #8 ·
i"t's a shame they don't do stroker height pin (B) pistons in 85.5mm"

can you explain a bit more please
 

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Paul Knight said:
it's a shame they don't do stroker height pin (B) pistons in 85.5mm, as that'd make life a whole lot easier. I built a very similar engine for a friend a few years back, but it wasn't as simple as we'd hoped (working on past experience with 'B' pistons and low CR). We neded up with thick spacers each side, which meant the tinware didn't fit properly and needed loads of fettling to sort, and there was a lot of clearancing to do on the piston skirts etc, as they weren't designed to move so far down the bore. In hindsight, we'd have saved a whole lot of time and effort by stepping up to 90.5s. Not only will the 2165cc motor offer more power, the CR on a normal case will usually work out somewhere around ideal for your needs (assuming the case hasn't been milled on the faces), and the pistons will most likely bolt right on.
Like I say, it's not impossible to do, but I'd rather step up the power, reduce the labour and have a stock-width motor with tight fitting tin every time!
AHA!
So, 90.5mm with stroker clearancing it is then (I did say plans subject to change at any point!)
Correct me if I'm wrong here but 90.5mm barrels have the same cylinder wall thickness as stock 85.5mm (1600cc) cylinders so I see that as being reliable for a Bay.

If I'm going for the clearanced 90.5mm barrels and pistons I may as well go for a bigger stroke crank as there's no price difference. 2165cc displacement sounds good! :)

I've been working/planning a fuel injection system incorperating programmable ignition advance curve for a few years now so it looks like it's gonna be needed!
 

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hermione_beetle said:
i"t's a shame they don't do stroker height pin (B) pistons in 85.5mm"

can you explain a bit more please
Have a look here:
http://www.johnmaherracing.co.uk/jmrshop/pistons.htm

You'll notice there's two types of 90.5mm piston and barrel sets. One has the pin moved closer to the bottom of the piston to allow more clearance (in this case it's for strokes of 82mm and above).
 

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I ran a 2165cc motor in my van for years and it never let me down or over-heated. Pulled like a train, too. That had big valve heads and an fk8 cam (with 1.4 rockers) but if I drove sensibly it would still give good economy and pulled from low rpm like a stocker
 

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Paul Knight said:
I ran a 2165cc motor in my van for years and it never let me down or over-heated. Pulled like a train, too. That had big valve heads and an fk8 cam (with 1.4 rockers) but if I drove sensibly it would still give good economy and pulled from low rpm like a stocker
Sounds cool! :)

I had been considering something like an Engle 100 cam for my engine although I'm still in two minds whether or not to retain the stock cam.
 

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see if you can find other folk with stroker motors and small'ish cams and ask for a ride. i did a couple 78x94s with 110 cams (for buses with cheap cranks :eek:) and they were torque monsters. 1st gear was pointless, easier to just pull away in 2nd and a flat torque curve to 5kish. Felt like a stockish powerband just loads more powerful. I think you'd be wasting a lot of potential by using a stock cam, or even a 100. The first one had kadrons and the 2nd 34ict's. the icts may have been a bit too small (less rpm from that one and a bit 'flatter' feeling), but gave good economy and were really easy to tune.

edit:- just dug out the spec and the 2nd motor was 78x90.5 - not that it makes much difference, it could still have lived with more cam!
 

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back in the day, old skool and all that ...... I used to trim bits off the bottom of non-VW pistons because it was not possible to get pistons with different gudgeon pin positions. You Volkswagen people have it so easy - all these bits and pieces - but it does appear to stop you think outside the box (fit any analogy you deem necessary) .

I used to trim quite a lot and even went as far as re shaping the skirt so that the crank could clear the skirt yet the thrust faces were still reasonbly long.

Anybody done this in this flat-four world?

If possible - it would let AngelV build a stroker motor with standard pistons etc.
 

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Paul Knight said:
see if you can find other folk with stroker motors and small'ish cams and ask for a ride. i did a couple 78x94s with 110 cams (for buses with cheap cranks :eek:) and they were torque monsters. 1st gear was pointless, easier to just pull away in 2nd and a flat torque curve to 5kish. Felt like a stockish powerband just loads more powerful. I think you'd be wasting a lot of potential by using a stock cam, or even a 100. The first one had kadrons and the 2nd 34ict's. the icts may have been a bit too small (less rpm from that one and a bit 'flatter' feeling), but gave good economy and were really easy to tune.

edit:- just dug out the spec and the 2nd motor was 78x90.5 - not that it makes much difference, it could still have lived with more cam!
Trouble is I think there's only one Bus I know of up norf with a seriously modified motor.
Still, that's given me plenty to think about though, cheers!

I never thought I'd be in danger of having too much torque!
 

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metric_thumbs said:
back in the day, old skool and all that ...... I used to trim bits off the bottom of non-VW pistons because it was not possible to get pistons with different gudgeon pin positions. You Volkswagen people have it so easy - all these bits and pieces - but it does appear to stop you think outside the box (fit any analogy you deem necessary) .

I used to trim quite a lot and even went as far as re shaping the skirt so that the crank could clear the skirt yet the thrust faces were still reasonbly long.

Anybody done this in this flat-four world?

If possible - it would let AngelV build a stroker motor with standard pistons etc.
Well, the standard pistons would be ok but hell, this is giving me a perfect excuse to go for 90.5mm ;)

I'm gonna have to save up for all the bits anyway so why not?
 

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AngelVenomous said:
Well, the standard pistons would be ok but hell, this is giving me a perfect excuse to go for 90.5mm ;)

I'm gonna have to save up for all the bits anyway so why not?
Damn!!
I was so hoping you would build a long stroke with standard pistons

I was so looking forward to reading what you got bhp/torque and mpg etc

Yes - my life is so sad someone else's figures are to stay up for

:) :) :)
 

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metric_thumbs said:
Damn!!
I was so hoping you would build a long stroke with standard pistons

I was so looking forward to reading what you got bhp/torque and mpg etc

Yes - my life is so sad someone else's figures are to stay up for

:) :) :)
Aw bless!
:hug:
(hey, everyone uses that damn emoticon on the chat section!)

Whilst I'm fine machining crank cases, I'm not too confident about machining pistons. I'm just really worried in case I take too much off. That said, I have some old barrels and pistons from the "donor" engine (one piston exploded but the rest are fine) so I could maybe get the crank first and observe the clearances with them and practice machining them.

Hmm........

What sort of problems are you likely to face when machining the piston crowns?
 

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I did 78x85.5 with stock heads, i was just saying it wasn't as easy as the 90.5 route. [email protected] and with 36IDFs about 20-25mpg in the bus (but that wasn't driven particularly carefully). However, there was little fuel economy difference from the stock 1600 motor it replaced.

As for cutting piston crowns, make sure they're forged pistons first and go steady, even at low CR it's easy to build up a lot of heat and pressure. speak to jmr.
i just cut the skirts about then sent them off to be balanced, i didn't touch the crowns, just used spacers to correct cr.
 

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why not use a 76mm crank with the right rods case clearence issues are minimal.
or try for the old 1776 cc twin 40s and engle 110 route that gives 100bhp at the flywheel all day long and you can use a std crank that has been 8dowled.
my bus was great with this combo 30+mpg and 70 mph easy
 
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