Bore & Stroke Kit

[cryin'wolf]

I've finally had some time to work on my bike, now that the hurricane season that left me near roofless is over and home repairs are mostly done. I tore the motor down and found 1 connecting rod journal .012" under spec. and both main journals at the .003" limit, which according to Honda requires one to replace the cases. Since I am not going to do that, and have found every imaginable bearing at Florida Bearing, I am going to replace them. I'm cocidering offset grinding the crank or modifing one from a VT1100. Would anyone be interested in a bore/stroke kit or parts list if I can come up with one reasonably priced at $600 or less.:happy:

[Mr.Sinister]

Yes! Long time no hear .

[Wild Coyote]

Huh? That was all in Spanish. What you talkin' about? More power? I'm up for that!

[cryin'wolf]

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1327Status as of 1/1/06:
So far just planning. I purchased a VT1100 crank, single throw type like the 750 's to illiminate the need to revamp cam timing and ignition timming for each cylinder. Most VT1100 cranks are 2 throw style which seem to be at 270 degrees from pictures, but I haven't actually seen one, surely it produces less vibration but definately more work to set up. The single throw will definately be an easier set up, as all the 750's periphral settings would remain the same degree wise.

Once the crank arrives I'll be able to measure it and see if it will work with the 750 case's bore spacing, width, and if the main journals will have to be turned down or the main bearings replaced with larger ones. I hope it will fit without much modifcation.

As with any stoke modifation the deck height of the motor is one of the biggest factors to over come. FYI Deck Height = Distance between Center of Crank and Top of Cylinder. This can be increased on most motorcycle engines by putting a spacer block between the case and cylinders.

I don't want to get into modifying my frame so I want to keep the stock deck height, though I have thought about raking the neck out some. However, the goal for the stroke mod is to come up with a combination that would be durable, easy to install for most wrenchers and require the least amount of machine work to keep the over all cost down.

With the 1100 crank's 15.4mm longer stroke the piston connecting rod combo has to lose 7.7mm of height inorder to fit. If the connecting rod jounals on the 1100 crank are the same as the 750's a pair of rods from a Toyota 4AGE will work with very little machining and a thrust type bearings (flanged).

I've pulled the sleeves out of the cylinders and think I can put up to 94mm pistons with sleeves in the holes, I'm shooting for 92mm's which would give me an overall package of just over 1200cc.

For mine, I want a 2 stage nitrous kit also, so I'll go with good after market rods. I've been designing a case girdle to help hold the case and cyliders and heads together. More than likely this will be the first thing actually completed on the project. I don't intend on using the bolt-on fins and will cut off the cylinder fins, but I have thought to make a finned version of the girdle if this kit idea actually works and someone wanted to keep a stock appearence.

The heads will get brought up to about 1100 spec through opening up the combustion chamers and larger valves. I want to keep the compression ratio at 9:1 - 10:1. I'm going to make a sheetmetal intake manifold a run a single carb similiar to DP's.

Camming I hope won't become to much of an issue. I think that with some messing around with the timming and rockers on the exhaust side, I could get this combo to run well. It has been my experience that mild cams take large amounts of air well if the engine can get rid of it fast.

Status 1/3/06:

I just un-wrapped the 1100 crank. This thing is huge and the connecting rods could probably replace those in my Ford 351W with no problem. As for the crank, boy did I make a mistake; this thing has no cam chain gear on the right side. Does the 1100 use 1 chain on the left side to turn both cams? I think I can get this thing to work, but by no means will this mod ever get to a cheap kit status with what I see as having to be my next course of action.

After measuring this thing out, it is feasable that it will work dimensionally with some machine work. The cheeks or couner balance weights are a monsterous 7.7" dia. and the outboard cheeks are about 1.2" wider comared to the 750's 5.880" dia. cheeks and will have to be cut down as expected and with the exception of not having a cam chain gear on the right side is marginally close to the 750 crank. The 1100 is longer, but with relatively the same main journal diameter which can be corrected by turning them down a few thousandths when the cheeks are done. The 1100 also has a slightly wider bore spacing, but this could be over come by bushing the connecting rods inboard by using flanged bearings. The outboard cheeks on the 1100 are The ends are where the difficulty lies. The tapered end for the flywheel is grossly different, larger in dia. though the the thread pitch is the same, also the as mentioned before the right side has no cam chain gear, and much longer.

The easiest thing to correct the end differences is to destroy the 750 crank by cutting the counter weights at the main journals turning the cheek and main portions down, indexing them, then cutting the 1100 crank ends at the main journals boring hole and index them, then pressing the 750 ends in, then welding them both on the inboard side of the cheeks for added security.

I've put pictures up so you can see the difference in size and a photoshop illustration of the proposed mod.

[RustyJake]

Looks like a job for the not to faint of heart. I know I wouldn't attempt it, I'm used to rough carpentry and some finishing, sounds like the tolerances are a little out of my league.
Hope it works out for you, keep us updated.

[ickmak]

I guess I'm dum :freak:





:eek2:

[Wild Coyote]

That is way out of my league!

[pegscraper]

Sounds like tons of work. What kind of HP gains you shooting for?

[Mr.Sinister]

If you get this figured out I may have to ride to Florida! Beer and wrenchin. So far I am still interested! I would like to keep my stock look without nitrous. This sounds like onsite parts canibalization/trade out. With the mods what kind of gain are we looking at ? 70-80 hp? This is very cool keep us posted!

[cryin'wolf]

Seat of the pants guestimation, figuring a marginally low for a motorcycle engine volumetric efficiency of 80% because of the stock cams, and no real numbers to base a calculation on other than bore and stroke and approximate air/fuel ratios, combined with a parasitic loss of 20%, 75 to 85 horsepower, assuming this thing will actually have a 92mm bore and 91.4mm stroke for a total of 1215cc. Real life naturally aspirated numbers can be much higher in the 90 – 150+ with professional head work e.g. flow bench, specific designed roller cam and rocker ratios, exhaust etc.

With the mind set that there’s no replacement for displacement, bigger is always better and even more is godly; I will fill the stock engine case with as much bore and stroke as she will take, adding structural support externally with girdles to tie the heads cylinders and case together, because the more fuel and air that goes into it, is potentially more power to come out. No ands, ifs, or buts about it.

Regardless of actual HP, I want to do this because I need an engine for my bike, I love tearing down and building up engines, and who else will have a 1200 - 1300cc 750 spirit???????? and Sinister you are welcome to come down whenever you want I always have beer and something to work on.

[cryin'wolf]

1/8 update:

About done with the templates. I made up a sheet metal axial profile template and radial axis templates of the of the 750 crank, and am in the process of making wood templates of the 1100 counter weights.

I've also been working on a grinding wheel add on to my lathe to use to cut down the 1100 counter weights, but it's not moving along as fast as I'd like.
I'm setting up to offset grind the 750 crank just to see how far I can stretch it and still have it work, also cut down the counter weights of the 1100 crank, and also make an entire crankshaft. This could possibly allow me to put together a kit that would only require one to have balanced before installation, though this is still far off in the future.

[Mr.Sinister]

Closer is better. I am picking up my old 600vlx next week. I might part it out for mod money. I have not seen it in 10 years since my brother laid it down. I am hoping it is in good shape and get me some money.

[Shadowflame]

I'd like to know how's this project coming along? I'm always interested in the quest for the Holy Grail of More Power. I think this mod is definitely the most extreme I've ever seen. Also, when do you hope to be complete with this work?:freak: