Big Bore Kit

[dragxs11]

Well I'd call it food for thought. But I don't think I'd go so far as to say this guy is the messiah for all our engines. I see the arguments, and they are valid ones. Just a little cautious to go hopping on the band wagon just yet. The port & polish thing would be a calculation that I don't think any of us could figure out. If it needs more restriction or less, or larger vs. smaller... Dunno.....I think I'll have to start asking around.
Matt

[strom]

The first time I read this stuff a few years ago, I was amased. Now... dunno.
The two pistons pic, his and conventional method.... well, one hasn't seen an engine.

Smaller ports, more velocity, same amount of gas/air mixture commin in. Oh, and it's harder to suck it in. Hmmm...

LP

[dragxs11]

Yeah, I thought about this a little. The breakin I can understand, but the port & polish is proven to increase top end HP. Smaller ports would increase pressure and give a little more low end. It's rob peter to pay paul either way. When you drag race, the engine never sees less than 4500 rpm anyway, so why would you care about the lower. Maybe I'm having trouble following, but what good does velocity do when the valve still shuts it off when the chambers full?
Respectfully submitted
Matt

[Pat Kelly]

Originally posted by ae7f


JB weld on the intake ports? Amazing stuff if it holds up and doesn't rattle loose with disastrous damage. That article and his performance results seem to back up his claims.

When my CB400TII (Hawk) snapped a connecting rod at 8,000 RPM it punched 2 holes in the cases. The oil pump, main bearing caps, and 'windage shield' (keeps crankshaft from dipping into the oil as it spins) were all cast as one piece. This assembly was shattered by the broken rod flinging around. I peiced it all back together and glued it with JB Weld. Worked for one season of racing and commuting. The hole by the primary drive gear did weep oil but that fell on the exhaust and burned off before ithad a chance to drip on the ground (also a sly way to keep the chain oiled). The JB help up admirably.

[Shuriken]

I've used JB to glue the end of a broken camshaft to the remaining peice that spins an ignition advancer. It worked for a ride or two. On the same thumper motor, someone had used it to repair a cracked crankcase. I later had it welded.

I'd like to see some scientific research on port size and characteristics in relation to performance. For example, take 4 stock heads from the same bike. Keep one head completely stock. Reduce port size on the other. Do 10k miles of tests, dynos, etc. Do the same with the next two heads only roughing up the port surfaces in one and keeping the other smoothe.

What does a turbocharger do? Doesn't it forcefeed extra air into an engine by increasing pressure by 5-10 psi? If it still goes through the carb it will still end up with the same mixture ratio, it just goes into the chamber faster, or more efficiently? Perhaps this guy is trying to do similar things with port size. If velocity increases with smaller openings shouldn't the mixture be just entering the chamber faster, or more efficiently?

He makes wild claims and seems to back it up with race results and dynos.... I would love to see more tests just out of curiosity. He has a dyno chart showing a head after being ported and polished as giving less horsepower, yet I've always heard the opposite as well.

Interesting stuff, but why doesn't every engine manufacturer follow the principle?

Ben

[Pat Kelly]

I seems that the net effect on power from increasing or decreasing the diameter of the ports would be related to the original ratio of runner size (diameter x length) to cylinder size (bore x stroke). Different configuration would react differently to any particular modification. As stated in an earlier reply, there are trade offs of power on top or bottom end of the RPM range. OEM designers have to please everyone, especially so back in the late 70 (before bikes became so specialized). That's why a V Max isn't a good touring bike, Goldwings aren't in motocross, and a CR125 isn't used in pro stock drag races

Most of my personal performace experience is in cars where you factor in where you want the power (top end or lower), transmission (manual or automatic and if automatic, what stall speed) and final drive ratio.

XS1100 is a darn good all-around bike, doing nothing exceptionally well (compared to todays bikes) but does everything very well. This leaves room to taylor the bike to your specific wants or needs. When touring you want a wide powerband to handle cruising speeds efficiently and elevation changes. If you're a city warrior you would benefit from low end power, all those red lights. If drag racing's your thing the top end power is what you are looking for.

One set of rules for engine modifications just isn't possible.

All that was too much thinking, I need to go for a ride

[Shuriken]

....but well said and right on the money.

Ben

[Sherry Shook]

big bore kits

To all big bore kit users... remember this is an engine it needs feul air and ignition... When you install the kits you have to feed the new cc's. If I were to install a big bore kit I first need to know how many cc's and the compression ratio. If you just install the big bore kit and do nothing else its going to run crappy. You need to do head work to make it breathe and do away with the original air box or at least modify. Next you need to dial up the mikuni carbs for more feul making jet changes. I also recommend changing the cams and get the lift and duration right for what you are building. last is the exhaust, I recomend headers so that the exhaust is tuned and can dump the increased exhaust. Some minor changes in the timing may also help. Then its nice to make changes and check power on the ol dyno till it maxes out. Another thing to play with is spark plugs you may need reduced lenght tips or differant heat ranges for the differant compression ratios. You have to experiment. Just a note from sherry's motorhead (and she is a dumb blonde) but raised around motorheads all her life!!!! LOL

[dragxs11]

I think we're getting off the subject a tad. I would still like to know more from those that have bored out.
Matt

[Snow]

...I just figured out that my problem is not my carbs... b/c my bike does seem to be consuming oil and I was pullin my hair out, I decided to replace my broken compression tester and make sure I didn't botch my big bore upgrade and here are the results:

Cyl 1: 65
Cyl 2: 135
Cyl 3: 75
Cyl 4: 155

Word of advice, use high quality ring compressors and not aircraft clamps! Well, I am going to at least measure my valve lash today to make sure when the shop put my head back together, they didn't switch my valve shims around on me.

[Sherry Shook]

big bore kits

Yo Snow I think a tear down is in your future either you lined up the ring gaps or have broken the rings upon installation. If it were valves it wouldnt consume oil unless the valve guides are very loose. To check take a compression reading dry and then add a teaspoon of oil into the cylinder, If the compression goes up considerably the rings are trashed. the oil seals the rings for the test. If the compression doesnt go up then the head gasket is blown or the valves are way out of specifacation
Sherry's motorhead

[Snow]

Yeah, I tried the teaspoon of oil and sure enough, compression went up about 30-40 psi per cylinder :/ I am checking on prices for new pieces now - looks like the ring compressor I'll need is around $40 or $50?

[TopCatGr58]

Botched Big Bore!?

Hey Snow,

I'm so sorry to see/hear about your extreme compression values with a new big bore kit! You mentioned a fancy professional ring compressor.....I just used my hands/fingers and nails, cause the cylinders were tapered at the bottom, was able to slide them down gently over the pistons and rings just fine! But getting some compression is better than none, which could indicate bent valves(BTDT). Checking your valve clearances is a good start, however if they were too tight, then you could already have burned or built up some crud/carbon inbetween the valves and seats, and that could also prevent a good seal and low comp's, but the burning oil problem is still nagging. How did you break in the new engine? Did you use a single weight oil for the first 500 miles?

If you do have to do a tear down, you may be able to save it with a simple honing and second attempt with a breakin!? If you find your valve clearances within spec, try the teaspoon of oil like Sherry said. If it does improve, then it's the rings, if is doesn't then it's the valves, might just need to relap them!? Also, are you positive of your valve timing, and chain slack adjustment? Just some words of encouragement, after my breakin, I got 180psi on my comp checks at sea level!! Good Luck.

[Snow]

I put 10w40 dino juice in for the first 500 miles, ran under 50 until 50 miles than under 55 for the rest of the 500 miles, tried to ride her gentle, but close to normal.

I am hoping that a quick honing will cure the problem, but I'll try to measure out the bores with a micrometer or such. I am almost sure we must have screwed up the rings the way we ended up putting them in - tried to use fingers for about 30 minutes and no-go, so we then used the large hose clamps...im kicking myself for that one...

My #4 cylinder reads 155 psi dry and right at 180 with a teaspon of oil

I am sure the ring gaps were lined up correctly, I was very particular about that at least

[fusionking]

65?

I think I would have went for a much harder loading on those rings during the break-in prosess. Read some of the stuff posted on this subject on this thread! It sure goes along with my 20 plus years of auto machine shop experience. If you break-in to easy you can glaze over the cross-hatch and wear off the part of the rings intended for break-in. Cam timing etc. would make all cylinders low. You have a very small window of opportunity to get it right. Don't waste it. If you don't believe me start reading info put out by the ring companies themselves! No break-in will help bad machine work. Make sure at least .003 of material is left for honing after boring and I would follow ring manufacture's advice on grit. You might get new jugs and still use pistons if they are any good still. Busted rings can do a number on cylinder walls and pistons. T.C. I'd say you got a good machinist cause he tapered the bottoms for you.