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680cc big bore kit for M600, is it worth it?

11K views 29 replies 12 participants last post by  SCDuc 
#1 ·
A motor swap is what I really want but it seems almost impossible since there are no 900 motors for sale in where I live. Is a big bore kit going to give significant improvement or is it just gonna be a waste of funds? I'm talking about the DP kit by the way..
 
G
#2 ·
Sell the bike, and go buy what you want. It will be cheaper, easer, better resale, and just a whole lot less hassle - Unless, your looking for a project, of which case - have fun.

A while back, a freind and I did a small block Chevy conversion on a pristine 1940 Chevy coupe. By the time we got through cutting the coupes frame, welding in a new subframe, replacing the rearend, wiring, exhaust, and making it all work, he had much more in it than if he had just gone out and bought what he wanted. However, him and I liked these types of projects, so it was a good weekend project.

Having pulled I don't know how many bike engines out and put them back in again after rebuilding; Unless you love projects, have a donnor bike to get the engine out of cheap, or love to wrench, my suggestion is sell what you have, and go buy what you want.

Brian F.
 
#3 ·
Selling the bike and buying a bigger one was an option but not anymore, I have decided to keep it and swapped the forks etc. Put relatively lots of time and effort on it, it gives me what I need which is a lightweight compact machine. It lacks the power on the highway when we return home after a day in the twisties. The power is more than enough for me at the twists anyway, I am not capable of turning them with more than 100 mph :p What I am looking for is a bit of improvement in the max speed with maybe a marginal touch of low and mid speed acceleration development. I will not be doing the job myself but labor is pretty cheap here. What I need to know is... is it gonna be a totally worthless mod or is it gonna be beneficial for the money spent, which I will spend if the kit does not get bid above $1000. After that figure I am off the auction no matter what.
 
#4 ·
It is not always the end goal that is what people want. I like the idea of the big bore kit. I know you could go out and buy an rs4r, but I am kinda like you I have lots of things done to my bike, I like it and I am proud of it. If you can get the kit for a fair price, I say go for it!!
 
#5 ·
if you are gonna swap motor, why not a 4v?

big bore kits give you marginal power increases and may or may not kill the reliability of your machine.

for the $$$, I believe that a stock motor out of a bigger salvage bike is cheaper than a smaller motor that's being pushed to failure.


Q
 
#6 ·
if you are gonna swap motor, why not a 4v?
I am not able to swap the motor cause M900 sales have been very limited here (so have been the bigger engined bikes for that matter) and it is almost impossible to find a motor off a salvage bike. Also, importing an engine is not a reasonable thing so swapping the motor is not an option.

big bore kits give you marginal power increases and may or may not kill the reliability of your machine.

for the $$$, I believe that a stock motor out of a bigger salvage bike is cheaper than a smaller motor that's being pushed to failure.
That's an interesting point and the kind of information that I am looking for. Thge kit is OEM, but it still is risky and may cause engine damage you reckon? If so I will not be doing it for an additional 12 hp (which the seller claims)
 
#7 ·
Having done some search I guess the big bore piston kit will not deliver any significant performance without high compression pistons. The kit in question here is a catalog item, 96401898C. Comes with
big bore 680cc cylinders and pistons, variable-advanced control unit, set of carbon fiber lowered silencers, Dynojet carburation kit + DP filter and claims to increase hp by 12 figures. I am not sure where the HCR gets in the equation here, or what ratio these cylinders/pistons have. Any comments?
 
#9 ·
Do you mean this kit
Yes. I asked the compression ratio and the answer is 12:1
 
#10 ·
qfactor said:
...big bore kits give you marginal power increases and may or may not kill the reliability of your machine...
I'm not sure on the marginal part. I had a Hawk GT racebike, 647cc stock had 48hp. Wiseco 700cc pistons upped to 65hp, thats nearly a 40% increase which is pretty dramatic.

I did also add Carillo cromo rods, pod filters, and jetted the carbs, and premium fuel was a must. I do agree about reliability, mine would require new rings every year but that might not be the case on a streetbike.

A big plus is that you will learn a lot about engines in the process.
 
#12 ·
#13 ·
Speeddog thanks for the link. Apparently it'll be worth it.
One thing though, are the certain specs mentioned in that article, such as:

"Cam Timing: Inlet Opens 31&Mac176;BTDC, Closes 88&Mac176;ABDC.
Exhaust Opens 72&Mac176;BBDC, Closes 46&Mac176; ATDC (CAM advanced an additional 3&Mac176;).
With Valve Clearance = 1mm"

results of the mod or necessary adjustments to be done with the mod? If this kit is not "plug and play" type and will need adjustments, I don't think I will be able to get those done...
 
#15 ·
Be careful with the DP kits like this though. If something breaks it wil be expensive and a PITA to replace.
Can you elaborate please? Someone else said ealier that engine failure risk is involved with this mod.
 
#16 ·
Well, the DP stuff is very expensive if purchased new. Lets say for instance that you break a ring and need to replace it you have to buy the full set of rings for both pistons and they are expensive.
If you can even get ahold of them where you are.

I am not saying the kits are unreliable as I have no first hand experience with them. The kit may last forever I don't know. I just know that locating replacement parts can be difficult and expensive.
 
#17 ·
Hey there, I'm gonna say that if you want the extra power the engine swap is most definitely the way to go... If you want the power of a 900 engine then this 680 kit is not comparable. My friend bought and installed this kit on his 2000 m600 and it was nothing but trouble... His engine is "overstressed" as he likes to call it, and is breaking down all of the time... You also need to consider an oil cooler which can be big bucks to install but necessary to keep temperatures down with the added combustion.
 
#19 ·
This started to sound a bit risky to me... I seriously wanted to do this mod but I don't want to risk the engine nor do I want to get an oil cooler. mywoody, what was the trouble your friend had because of this kit? "overstressed" as in "overheat" ?
 
#20 ·
They mean that the engine's reliability to reproduce the same level of power isn't consistent due to the extra "stresses" applied on all components.

A better way to get to where you want to be is to sit down and make a "Design" plan.

1) how much power do you want? (60, 65, 80, 100 hp?)

2) how reliable do you want the bike to be? ( 200 mi/day, 200mi/week, 200 mi/month ?)

3) how hard is it to find replacement parts? no matter what it is, new or not, it will need to be replaced one day or another, for various reasons, it be human error (not obvisouly yours tho) or mechanical failure.


now research the cost of all the parts (including regular maintenace items for a year or so) for each options, figure out what you can and can't afford.

enjoy.

Q
 
#22 ·
12:1 is way too high for a road bike ime. 10.5 is good, altho the smaller bore can get away with more.

the biggest issue with the 600 power wise is valve size - they have the 400 heads. the 620 has 35cc more and 750 valves and makes lots more power comparitavely. but you can't fit bigger valves to a 600 head easily. you could get some 750 heads and fit them, but then the chambers are quite a lot bigger, so you'd need some high comp pistons to suit. or get a 750 crank from a same year/alternator style bike and some 620 pistons and make it a 620.

what year 600 is it? up to '97 the cases are different to 750 - smaller cylinder spigot, but '98 on you should be able to fit 750 cylinders as well as a 750 crank and heads. even fit an 800 crank and big bore kit for 850 or whateve you can get. 750 stuff is pretty cheap on ebay.

and you'd need an oil cooler too, altho everything else in a 600 is pretty much the same as a 750. shouldn't be any reliability issues of the comp isn't too high.

all this is why no one modifies 600 engines pretty much.
 
#23 ·
I am not sure if that 12:1 is a correct ratio, it is a DP catalog item and at the link that Speeddog provided the bike uses same kit with a comp. ratio of 10.3:1 and I think this is the true ratio. Anyway, from what I heard from you guys I decided this is a risky mod and haven't bid for the item.

brad, are you saying that I can improve the engine not by an outright engine swap but by swapping some components of the engine? If so, that may be possible for me since I may buy parts off ebay, that way I will not be importing a whole engine but "engine parts" which'll be lot easier. You have listed few parts (maybe all) but can you please tell me what I will need to convert a 600 enine to a 750 ? It is a 2000 M600 by the way.
 
#24 ·
apart from the crank, cylinders, pistons, heads, inlet manifolds and carb jets the 600 and 750 for comparitive years are pretty much the same. the crankcase part numbers for '98 on are the same for 600 and 750. the rods are the same, gearbox is the same. not sure if the clutch is different or not, but i don't think so.

so building it up into a 750 is pretty easy. or an 800, which is just a stroked 750. or use 800 big bore pistons and a 900 crank for even more cubes - you should be able to get it to 875 or something like that i think. will require an oil cooler. bruce meyers has lots of experience building little motors to last.
 
#25 ·
Thank you very much brad.
What is your opinion about this DP kit overstressing the engine? If the CR is 10.5:1 (not 12:1), do you think it is acceptable and safe?

edit: I haven't seen it, you've already said it was good. thanks.
 
#26 ·
the std 600 is specced at 11:1 or something like that. they have a lot of comp because they run 400 heads. the pistons have a bowl in them, whereas all the other 2v pistons have a dome of some sort.

plus it's only a 600. all the stuff in it is designed for a 750 anyway. the only issue with comp is detonation, etc, which can be nasty. you could machine the piston crowns or your chambers if you wanted to lower it anyway.
 
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