Performace engine rebuild - Sportbike Forum: Sportbike Motorcycle Forums
 
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post #1 of 8 (permalink) Old 01-01-2003, 11:25 PM Thread Starter
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Performance engine rebuild

Hello, I have a cb750 that runs pretty well. I want to get the engine and trans rebuilt. I will need to depend on this bike so Im going to get the engine rebuilt so it cant die on me. Now since the engine is going to be worked on what are some sugestions for improving performace? valve job? whats this piston coating I hear about. Reliablity is #1 concern. Any sugestions or reading material would be nice.

EDIT Its a 1980 bike so its DOHC, if that makes a diff.

If it aint broke, fix it so it is.

Last edited by pagefault; 01-01-2003 at 11:51 PM.
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post #2 of 8 (permalink) Old 12-25-2006, 10:19 AM
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You don't have an especially large selection with a Honda. Building a Kawasaki or Suzuki, on the other hand presents a far larger selection. They're a lot like souping up a Chevy small block. The problem in trying to decide what to use. The subject is too large to cover here, but give me a call at the shop at (770) 761-9800 and I can give you some recommendation or ideas. Here's photo of my shop so you don't think we're some back alley garage somewhere.
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post #3 of 8 (permalink) Old 12-25-2006, 03:07 PM
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Higher compression pistons, port and polish heads, cams, and exhaust, low weight fly wheel. balance and sharpen crank.

A few ccs short of a full litre.
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post #4 of 8 (permalink) Old 12-25-2006, 03:55 PM
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That's rather meaningless advice there Mac020.

Port & polish: Porting is a good way to kill performance. Most builders on today's sportbikes value port velocity over volume. We also learned about 20 years ago that polishing your ports is a really bad idea.

Cams: This depends on how the bike is used. More aggressive cams will help at the top end but will kill the first half of the RPM range.

Lightened flywheel: What in the heck is a flywheel on a sportbike? You might consider balancing the clutch basket.

Lightened & sharpened crank: I'll give 50% on this one. Falicon calls it a supercrank. They lighten the crank, polish it, and precision balance it. It certainly isn't 'sharpened' however. (This probably comes from a misunderstanding of the term 'knife edge' crank. The end result is about as sharp as a bowling ball. (Poor terminology).

This is why I chose not to just toss in a few flash cards. It really requires far more room than is afforded here to give a meaningful response to Pagefault's question, which is why I gave him my phone number instead. This reminds me of taking Brain Surgery in three easy lessons. You might want to give it a little more thought. This is why the typical website is a terrible source of information on such an involved subject. Responses are usually well intended but false, mis-leading, mis-guided, over-simplified, or just plain irrelevant.
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post #5 of 8 (permalink) Old 12-25-2006, 04:48 PM
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Guess it's what you are looking for as far as performance and I'll admit I don't know much about most Japanese bikes.

I looks like you defiantly know a lot more about bikes than I do but I have done most of the above to my bikes and personally liked the results.

I really don't understand your flywheel comment as my Ducati has one.???? I know using a lighter flywheel doesn't increase horsepower but it does decrease the rotating mass allowing for quicker acceleration.

I also don't understand your velocity over volume comment as I thought a good polishing would allow for better (laminar) flow. (More velocity)

The "sharpened crank" is done on some Ducati race bikes. The knife edge cuts down on the drag that is created as the counter weight goes through the oil.

I thought I throw out a few Ideas so the gentleman could decide for himself and he asked for some ideas.

If you want to drum up some business here that's fine. But personally from the tone of your post I don't think I'll be visiting your shop anytime soon.

A few ccs short of a full litre.

Last edited by mac020; 12-25-2006 at 04:52 PM.
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post #6 of 8 (permalink) Old 12-26-2006, 01:30 AM
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now now children play nice hehehe.
my recomendations are before you go tearing into your bike look at the compleat bike and its overall condition, see everything it needs tires, suspension and look at the condition of the engine like the clutch (check condition of the clutch see if parts are worn out ) do a compression check see if you have good compression. you said you want reliabilty just freshening up what is worn will help with performance and reliabilty.

scott
2002 CBR 954 RR
when you are on a honda you are on the best
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post #7 of 8 (permalink) Old 12-26-2006, 05:09 AM
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Aw screw it! This post is almost 3 years old anyway!

A few ccs short of a full litre.
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post #8 of 8 (permalink) Old 12-26-2006, 05:25 AM
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Sorry Mac020 if you thought I was attacking you, I wasn’t. I get a little frustrated when someone responds to a question without really doing his or her homework. If you know the answer, that's great, but to just toss in a few ill-advised 'tips' is really a dis-service. The party asking the question often jumps right on the his new found knowledge and things go down hill from there. I once read where a guy asked how tight to adjust his chain and the first response was to tighten the chain as tight as possible. He replied "Thanks Bob, I'll tighten it really hard tonight when I get home from work. Boy I sure love this website, who need a service manual". Well here again the response was probably well intentioned and most likely came from overhearing a drag racer discussing the subject. Sometimes a little knowledge is a dangerous thing. The big problem with any Website is the inability to really get into any complex topic. Few people want to read a long drawn-out dissertation on anything. I usually find that responding to this sort of question does nothing to help the person in any meaningful way. I've written several magazine articles on this subject and the biggest problem is trying to condense the material to just a few pages with support photos and charts.
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