Short Stroke 750 Build

RennieK said:

What kind of lifters do you use in those cylinders?

I'm curious if anyone has experimented with coated aluminum alloy liners and pistons for the alloy barrels.

It just seems the steel liners in spite of their durability seem to be problematic and I would guess due to the differences in expansion and contraction rates of the different materials. Further more the temperature differences at the top of the cylinder compared to the bottom must compound these expansion/contraction rate differences and could explain the types of breakage's experienced with the Dunstall cylinders and liners.

I'm wondering if alloy barrels, liners and pistons with nikasil, ceramic or nitrated surfaces would work although I have no idea of the cost of putting it together. I know it wouldn't be cheap until someone starts putting a kit out (if it indeed could handle it)

How bullet proof are the Maney kits?

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The cylinders use stock Commando lifters.

Kenny Dreer used Nicasil (or a similar surface treatment) on some of his 880 cylinder kits. He's the only one I know of who's done so. I now Steve Maney looked into it, but decided to stick with high quality iron sleeves. I discussed it with him at the time, but I don't recall his reasons.

I think the problems with the Dunstall kits was that the liners were really thin on the 810 kits, and the alloy used for the cylinders was fairly soft. You can get away with using liners as thin as 1/16" in the iron cylinders, but not in the alloy cylinders.

The Maney stuff is as good as it gets. He's really committed to making very high quality parts.

Ken

Latest update. After removing the main bearings I discovered that the drive side fell out with no heat applied (after removing the anti-rotation pin). The bearing bore in the case is now .001" larger than the bearing, where it should be .0025" or so smaller. Although it ran fine that way (127 mhp at Bonneville), I'm not willing to run it again without repair. I will eventually fit a bronze sleeve to recover the right fit, but I think to save time I will use another set of cases. Because these are MK3 cases, I only have one other set that is suitable. Back when Steve Maney was only casting the drive side halves, I had him fit one to my MK3 timing side. I was intending to use that with a Nourish 91 mm stroke MK3 style crankshaft to bring back a big bore engine I'd raced with years ago, but haven't managed to get to that project. Now, I think I'll use it for this engine, and later repair the other cases for the big bore. The pics below show the "half Maney" cases.





Ken

That's very nice looking back up. These cases look considerably thicker.

Thanks also for the replies above.

I always thought the Nourish gear was all about the head. Was the stroker crank "normal" or is that your own doing?

lcrken said:

Latest update. After removing the main bearings I discovered that the drive side fell out with no heat applied (after removing the anti-rotation pin). The bearing bore in the case is now .001" larger than the bearing, where it should be .0025" or so smaller. Although it ran fine that way (127 mhp at Bonneville), I'm not willing to run it again without repair. I will eventually fit a bronze sleeve to recover the right fit, but I think to save time I will use another set of cases. Because these are MK3 cases, I only have one other set that is suitable. Back when Steve Maney was only casting the drive side halves, I had him fit one to my MK3 timing side. I was intending to use that with a Nourish 91 mm stroke MK3 style crankshaft to bring back a big bore engine I'd raced with years ago, but haven't managed to get to that project. Now, I think I'll use it for this engine, and later repair the other cases for the big bore. The pics below show the "half Maney" cases.

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What is the advantage of the Maney case? Better material and/or reinforced design?

hi swoosh,answer to your question,both

The Steve Maney crankcases are extremely strong and pretty much bulletproof- vastly stronger than a stock Norton crankcase: I twice cracked drive side bottom ends when I first started racing before finding the Maney stuff. That being said, I am one of the very elite few who managed to blow one up catastrophically when I had a rod bolt shear when I happened to be doing close to 130mph on the banking at Daytona last year- I put a rod through the front of the case and blew it to pieces. Didn't do me any good either, breaking pieces off my T3 to T6 vertebrae and knocking me out for a while. But I recovered enough to go to on crash two more times last season! Don't ask....
The short stroke that Herb built was actually a centre main bearing crank design of his own creation- very fast but needed lots of maintenance and suffered from some oiling issues with the centre bearing oil feed pressure.
I have used the throughbolt 850 style 750cc barrels which Walridge Motors used to sell (maybe still do? ...not sure) to good effect- much cheaper but of course much heavier than the Maney alloy ones which I have on there now.

Not sure if I want to cry over the cases or the BARREL. :cry:

Not a racer but very similar to my failure, 3000 mile bolt at 4000rpm. Something in Paul Dunstall's book about cleaning up this part of the bolt for racing. I did notice the bolts on my new rods (early new forgings from end 2002) have polished waisted section, no spiral tool marks as on the failed part.
Didn't bend the other bolt but look at the cap. Saved the crank but lost cam, piston and nice Maney barrels and the cases! Rebuilt with 850 look-alike 750 barrels you mentioned.

Doug MacRae said:

The short stroke that Herb built was actually a centre main bearing crank design of his own creation- very fast but needed lots of maintenance and suffered from some oiling issues with the centre bearing oil feed pressure.

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Can you elaborate a bit more on this? Was that a bespoke crankcase or modifed Norton parts with an extra middle section? I kinda like the idea of a third bearing and am toying around with the maths how to do it...


Tim

RennieK said:

That's very nice looking back up. These cases look considerably thicker.

Thanks also for the replies above.

I always thought the Nourish gear was all about the head. Was the stroker crank "normal" or is that your own doing?

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Rennie, if you'll look back at my earlier post on this thread with the picture of the crank and a discussion of it, I think that will answer your question about whether it was "normal". If I've misunderstood your question, please post the it again, and I'll answer it.

Dave Nourish has made his one-piece crankshafts for both Nortons and Triumphs for several decades now, even though he is better known for the 4-valve heads and engines. I've used several of them, and the only problem with them is that they are generally heavier than most Norton builders like. This particular one is lighter because of the large holes Dave drilled in the flywheel, but last time I talked to him, he wasn't offering that as an option any more. On the new engines I'm building, I"m now using Maney cranks. They are very high quality, and the three piece design allows you to make them as light (or as heavy) as you wish.

Ken, I get it now. I'm in a 750 mind set and was thinking 73x91=stroker even though I just checked my manual to see the 750 stroke is 89 stock. I'd been thinking the bores and strokes were closer together numerally. I guess the bore of the 920 is more like 83. I have to go do my homework now.

Doug MacRae said:

The Steve Maney crankcases are extremely strong and pretty much bulletproof- vastly stronger than a stock Norton crankcase: I twice cracked drive side bottom ends when I first started racing before finding the Maney stuff. That being said, I am one of the very elite few who managed to blow one up catastrophically when I had a rod bolt shear when I happened to be doing close to 130mph on the banking at Daytona last year- I put a rod through the front of the case and blew it to pieces. Didn't do me any good either, breaking pieces off my T3 to T6 vertebrae and knocking me out for a while. But I recovered enough to go to on crash two more times last season! Don't ask....
The short stroke that Herb built was actually a centre main bearing crank design of his own creation- very fast but needed lots of maintenance and suffered from some oiling issues with the centre bearing oil feed pressure.
I have used the throughbolt 850 style 750cc barrels which Walridge Motors used to sell (maybe still do? ...not sure) to good effect- much cheaper but of course much heavier than the Maney alloy ones which I have on there now.

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Dave,

thanks for posting the pictures and info. I talked to Herb a while back about the engine, but the pictures are much more vivid.

I'm using Maney cases now, as well as the one remaining stock case with welded reinforcements, because I broke several stock cases back when I was racing Nortons. Back then, it was common for the stock case to crack on the drive side after enough flogging on the track. The crack would typically start at the back of the drive side case where it is thin, and progress around to the output shaft bearing bore. It looked like the top end was trying to pull the top of the case off. I had that happen on at least four cases (maybe more, my memory is not what it once was). I only had one case where the timing side developed a crack in the same area, and that was one where the crack on the drive side had gone all the way to the output shaft, and you could see a gap in the case. None of these engines broke from problems with the crank or rods, just from fatigue and lots of racing miles. The Maney cases are so sturdy, that I can't picture breaking one unless something gives out internally, like your rod incident.

I have only had one engine actually grenade. That was an original factory short stroke 750. They came with steel rods instead of the usual aluminum/steel design. If I still have one around, I'll take a picture and post it. Unfortunately, the factory decided they were too heavy, and lightened them (acid dip, I think). One of them broke at a race at Steamboat Srings, and sawed the cases to pieces. I found afterwards that the factory steel rods had a reputation for doing that. I quit using them, and switched to Carrillo rods. I've used the stock aluminum/steel rods in a lot of race engines, and never had one break. I have replace them when I found cracks around the pin end, and I've seen enough break in other engines, so I now only use the Carrillo rods. I still think the stock rods are pretty good, as long as you inspect them for cracks, and replace them every full season or so, but I'm not willing to take the risk myself. I used to have them shot peened, and had the rod Zyglo inspected, with the cap and bolts Magnafluxed every time an engine was apart. I think that helped a lot with the reliability.

Ken

RennieK said:

Ken, I get it now. I'm in a 750 mind set and was thinking 73x91=stroker even though I just checked my manual to see the 750 stroke is 89 stock. I'd been thinking the bores and strokes were closer together numerally. I guess the bore of the 920 is more like 83. I have to go do my homework now.

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My mistake, Rennie. I forgot I'd mentioned the 91 mm stroker crank, and thought you were referring to the short stroke 750. Sorry about that.

For reference, the short stroke 750 is 77 mm bore and 80.4 mm stroke. The usual 920 is 81mm bore and 89 mm stroke. HPI used to sell a 940 kit with 82 mm bore, but the sleeves were just too thin, and they didn't work well. When I was racing the engine with the 91 mm crank, I was only using an 80.5 mm bore, which gave me just a little over 920 cc. With the usual 81 mm bore, it would have been 938 cc. Another good combination is what Steve calls the ultra short stroke 750. That's his 75 mm stroke crank with a bigger bore, 79.5 mm for 745 cc, or 81 mm for 773 cc, the maximum legal for AHRMA 750 classes.

To get the 83 mm bore, you have to use the special cases and cylinders from Steve, which move mounting bolts further apart to allow a wider bore spacing. That also requires moving the head bolt locations, and opening up the counterbores in the head for the new larger, more separated, bores. You can still use a standard crank, but it needs a wider flywheel. That combo would give you 963 cc. If you add Steve's 93 mm stroke crank, you get the 1007 engine. If more is better, too much is just right!

Ken

Can you elaborate a bit more on this? Was that a bespoke crankcase or modifed Norton parts with an extra middle section? I kinda like the idea of a third bearing and am toying around with the maths how to do it...

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Herb's first short stroke centre main bearing motor was in a machined from billet drive side case- this progressed to a Maney case with a centre main bearing support that bolted into the case. Crank had two skinny flywheels on each side of the centre bearing which has it's own oil feed. Access holes in the bottom of the crankcase allowed for different 'heavy metal' slugs to be screwed into the crank to alter the weight of the crank. He also built a Seeley framed 500 Dominator based short stroke to compete in 500 GP. They both work well but require a lot of maintenance.

Great information Ken. There's a lot that goes into achieving a 1007!
I'm wondering how the first Norton 750 production short stroke race machines were configured. Was it longer rods or did they have special barrels or was it a combination of things?

RennieK said:

Great information Ken. There's a lot that goes into achieving a 1007!
I'm wondering how the first Norton 750 production short stroke race machines were configured. Was it longer rods or did they have special barrels or was it a combination of things?

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Rennie,

the factory short stroke 750s used standard crankshaft forgings, but machined for 80.4 mm stroke. They had longer steel rods, 6.200" center-to-center, compared to the stock 5.875". They used 850 cylinders, with the standard 77 mm bore. Some of the race engines had tuftrided bores, but I don't know if the customer engines also had them. The pistons were made by Omega and had a domed top. They used a slightly larger pin, .750" instead of the stock .6868". The heads were made from standard castings, but had the intake valves re-angled from the normal 28 degrees to 26.5 degrees, to allow a larger inlet valve. They also were machined with a full hemi shape, with no squish area. The engines came standard with the 4S cam. I thought I had an old rod I could photo and post, but it looks like I didn't save it. I do have a couple of the original pistons, and I've posted the picture below. In my earlier post I showed the same pistons with the domes and valve reliefs modified for my engine.



Ken

lcrken said:

I thought I had an old rod I could photo and post, but it looks like I didn't save it.

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Ken,

Do these look like the 750 short stroke steel rods?

hi lab,yes they are the ones ,identical to the pair i have,allen headed bolts instead of the normal conrod bolt and nut,also to add to the post by ken the short stroke pistons had a different deck height [pin to crown] than std pistons

A little more progress. I'm back to using the welded cases I started with. These pictures show some of the steps in fitting a bronze sleeve to restore the main bearing bore fit.

First is boring the case to a larger diameter.



Then turning the OD of the sleeve from a cored bar of CDA 954 aluminum bronze.



After parting off the part, it is bored to a rough undersize, to be finished after it is installed.



A shot of the case with the sleeve before installation.



And finally, the sleeve installed in the case. Next step will be to bore it to size, machine for the retaining washer, and shrink the bearing in.



Ken

Thanks for the intresting thread, I'm curious as to what you actually are using as a set up register, as you appear to have turned and bored the sleeve in two steps, and you have removed the case from it's original set up, I suppose my question really is how are you keeping the tunnels in line, :?: