Topic: ENGINE HOSED(???)

[longshanks]

The worst has happened!     The mechanic working on my bike after starting it up heard a clacking noise coming from the case. After dropping the oil pan he found some metal shavings, some steel, some aluminum. I'll go and listen to it tomorrow and if it sounds the same then all along I was thinking it was a noisy cam chain when in fact it could have been a worn rod bearing.

I'm so bummed I can't even express it. I just put hundreds of dollars into it. New steering head bearings, new tires, new fork seals, clutches and clutch cable, carb rebuild, carb boots, starter motor, spark plugs and caps, etc. All of it was gearing up to go on a long cruise with my brother and now I'll have an expensive brick sitting in my garage

I'll try and take some video of it running tomorrow and perhaps you guys can help me diagnose it. If it's truly a goner engine should I look for a used one or get ambitious and open up the whole engine and rebuild? I always planned on going to 836 and getting some head work done on it. I'm pretty broke now so it all seems so far off.

[OneWheelDrive]

Oh no!  Typically the least expensive option is to find a motor from a parts bike and just swap.  That's what I had to do with my first 550 project.  When you look at what it takes to rebuild a motor, especially one with significant damage, it could be way less than half to find a donor.  Then again, you take a risk buying a motor at the promise that, "it ran when I pulled it out of the bike..."  Good luck!

[dave500]

the money youve spent on it so far isnt gone or wasted,those parts are still good,bummer though,maybe a used going engine and shelve the old one for its 836 re birth when your more financial?

[longshanks]

So the mechanic offered to swap a K1 engine he has that is fully built with carbs ready to go for $650 after the core charge for my old K6 motor. Or, he has a stock K5 that is in pretty good shape (I've checked it out in person) for $2500 or $1500 if I swap my bike for a $1000. However, the K5 has about 56,000 miles on it. The stock K5 would have a better resale value than my chopped cafe'd bike but it has so many miles and the K5 engines were not as powerful as the K1's. I'm torn...

Suggestions?

[754]

 Can you pull the motor/ stock motor used parts are cheap, as are used motors. is the k1, by saying built..a rebuild or hopped up ?

[longshanks]

Can you pull the motor/ stock motor used parts are cheap, as are used motors. is the k1, by saying built..a rebuild or hopped up ?

K1 is rebuilt. But doesn't the K1 have at least 10hp on the K6 motor?

[Duke McDukiedook]

That K1 might be not be a bad way to go if you don't have the time and resources to buy a motor used and put it in yourself.

[Tim2005]

Maybe I'm being a tad cynical, but it's an odd coincidence that the mechanic who chanced upon a major engine problem just happens to have a rebuilt motor available to fit...

[Terry in Australia]

Who told you that the K1 engine has an extra 10 BHP over a K6? Seriously, while the story goes that as Honda evolved the mighty CB750 it was slowly "detuned", a difference of 10 BHP is a load of crap.

You probably won't notice the difference unless your engine was in a pretty poor state of tune mate, but then again, if your engine was slowly destroying itself, you'll probably think the new one is fantastic.

If money is tight, 650 bucks fitted sounds like a good deal to me, but like you say, an unmolested K5 will be worth way more than a butchered K6, as much as the cafe guys think that taking a hacksaw to a classic CB750 is uber cool, in years to come the stockers will be a lot more valuable. Cheers, Terry.  

[754]

 I cant remember any quick k5 or k6 stockers, but I would   rather have a 71 motor than the late ones..

[longshanks]

Maybe I'm being a tad cynical, but it's an odd coincidence that the mechanic who chanced upon a major engine problem just happens to have a rebuilt motor available to fit...

Thought someone would say that. He's actually a really honest guy and doesn't really want to let go of the K1. He'd rather I exhaust other options before I would consider buying it off him.

[longshanks]

Who told you that the K1 engine has an extra 10 BHP over a K6? Seriously, while the story goes that as Honda evolved the mighty CB750 it was slowly "detuned", a difference of 10 BHP is a load of crap.

You probably won't notice the difference unless your engine was in a pretty poor state of tune mate, but then again, if your engine was slowly destroying itself, you'll probably think the new one is fantastic.

If money is tight, 650 bucks fitted sounds like a good deal to me, but like you say, an unmolested K5 will be worth way more than a butchered K6, as much as the cafe guys think that taking a hacksaw to a classic CB750 is uber cool, in years to come the stockers will be a lot more valuable. Cheers, Terry.

I'm going off the Thoughts of Hondaman. He said the K1's early/late models made 61/58hp to the ground. While the horsepower isn't stated for anything after K5 he mentions K5's made noticeably less hp than his K2 which puts about 45hp to the ground. It's a good bet a average stock K6 puts 40-50hp to the ground, no?

And yes, my old engine was a little tired. About 120psi in all cylinders.

I agree with you about cafe's. There're already on their way out and it's only a matter of time before stock CB's are the thing to have for the majority of people out there. 50k on the clock is a lot though...decisions :/

[crackerbat]

Who told you that the K1 engine has an extra 10 BHP over a K6? Seriously, while the story goes that as Honda evolved the mighty CB750 it was slowly "detuned", a difference of 10 BHP is a load of crap.

You probably won't notice the difference unless your engine was in a pretty poor state of tune mate, but then again, if your engine was slowly destroying itself, you'll probably think the new one is fantastic.

If money is tight, 650 bucks fitted sounds like a good deal to me, but like you say, an unmolested K5 will be worth way more than a butchered K6, as much as the cafe guys think that taking a hacksaw to a classic CB750 is uber cool, in years to come the stockers will be a lot more valuable. Cheers, Terry.

I agree with you about cafe's. There're already on their way out and it's only a matter of time before stock CB's are the thing to have for the majority of people out there. 50k on the clock is a lot though...decisions :/

Replace the speedo if the mileage bothers you ... i got 67k showing on my f1, and only a top end rebuild has been needed.

[Terry in Australia]

Who told you that the K1 engine has an extra 10 BHP over a K6? Seriously, while the story goes that as Honda evolved the mighty CB750 it was slowly "detuned", a difference of 10 BHP is a load of crap.

You probably won't notice the difference unless your engine was in a pretty poor state of tune mate, but then again, if your engine was slowly destroying itself, you'll probably think the new one is fantastic.

If money is tight, 650 bucks fitted sounds like a good deal to me, but like you say, an unmolested K5 will be worth way more than a butchered K6, as much as the cafe guys think that taking a hacksaw to a classic CB750 is uber cool, in years to come the stockers will be a lot more valuable. Cheers, Terry.

I'm going off the Thoughts of Hondaman. He said the K1's early/late models made 61/58hp to the ground. While the horsepower isn't stated for anything after K5 he mentions K5's made noticeably less hp than his K2 which puts about 45hp to the ground. It's a good bet a average stock K6 puts 40-50hp to the ground, no?

And yes, my old engine was a little tired. About 120psi in all cylinders.

I agree with you about cafe's. There're already on their way out and it's only a matter of time before stock CB's are the thing to have for the majority of people out there. 50k on the clock is a lot though...decisions :/

No mate, with all due respect to Mark (Hondaman) the only difference of note between the K1 and K6 is the HM300 pipes on the K1, the HM341's on the later models were a little more restrictive. More than likely you're not running either pipe on your bike, so like I said, you won't notice the difference. ALL CB750's are quoted as producing 67 BHP except the F2/3 which produced 71, so unless someone can show you a dyno card, it's just an opinion. Cheers, Terry.

[Stev-o]

If I was in your situation, I would probably go with the K1 motor and get it back on the road.  650 does not sound like a bad deal.

[seanbarney41]

Somewhere on here Hondaman has a thread about changes made over the years that reduced power...the main two I remember are the more restrictive exhaust and less ignition advance built into the advancer...both pretty easy to change to '71 spec (or better!)...that being said, I recently pulled my K1 motor for a top end rebuild and am using a k7/8 temporarily in its place.  The  k7/8 motor really doesn't feel like it has the top end power of the k1.  The k1 felt like it made power up to and beyond redline.  The k7/8 seems to run out of breath before 9 grand.  I think I will try dropping in an early advancer and see how that does...

[mycb750k6]

Terry,
With all due respect to you, there's an extensive laundry list of things beyond pipes contributing to the de-tuning of the later Ks including cams, advancers, porting, ad nauseum, all well documented here, there and everywhere. 


Long live the mighty K1. [size=78%] [/size]

[DedHed]

If it were me (And I'm glad it's not!).... I would buy the running engine and shelve and rebuild the current engine.

I have a very decent stock engine on my 750, from what I can tell it has never been rebuilt and currently looking for a "Blown" or siezed engine now to 1) learn how to tear apart and 2) possibly have a spare for the worst case scenario with my running engine.

That is a drag losing the bike here at spring-time, but maybe it's an opportunity.....

Good luck with it!
Phil

[Rigid]

Maybe I'm being a tad cynical, but it's an odd coincidence that the mechanic who chanced upon a major engine problem just happens to have a rebuilt motor available to fit...

Maybe he is just involved in the maintenance of these old machines and picks up used motors when he can.  I have many spare engines for just such on occasion as the original poster described.  Never get caught short when it comes to a blown engine, they are too easy to swap and too cheap to pass up in project bikes.

[Ernest T]

Why was your bike in the shop in the first place?

[Terry in Australia]

Terry,
With all due respect to you, there's an extensive laundry list of things beyond pipes contributing to the de-tuning of the later Ks including cams, advancers, porting, ad nauseum, all well documented here, there and everywhere. 


Long live the mighty K1. [size=78%] [/size]

Yeah, I've seen the "laundry list" here mate, but funnily enough, I've never seen a dyno card to back it up? Where's this 10 BHP coming from? Let's face it, the go-fast boys are getting their engines bored out to 836cc, using 10.25:1 high compression pistons, ported and polished heads with bigger inlet and exhaust valves, high lift cams, 29mm or 31mm CR carbs, 4 into 1 race pipes, electronic ignitions etc, and they're getting an extra 20 - 30 BHP, but SOHC4 folklore states that a K1 engine with the same basic spec as a K6 engine somehow produces an additional 10 BHP? How can that be? Honda magic? More like "Tall tales and true, from our legendary past..............."      

[Don R]

Back in the day, as we old farts say, it was common knowlege Honda took a bit of power away from the 750's. Insurance companies and other authorities were alarmed by how many crashes there were and honda was pressured to back them down a little. These bikes were considered dang fast back then and a lot of new riders were getting right on them.

[Terry in Australia]

Yeah, I've heard those stories too Don, but considering that by 1972 Kawasaki was producing the legendary Z1 with way more horsepower and top end speed than the CB750, why would Honda want to detune their bikes if they were trying to compete for sales against Kawasaki's new rocket ship? And why would they suddenly change their minds in 1977 and up the BHP for the F2/3?

My stock K0 felt a lot "peppier" than my K1 or K2, but that was because the cable carbs on the K0 had lighter return springs on the carbs than on the later bikes. I think if installing K1 parts on a K6 would give you an extra 10 BHP, there'd be a lot of folks doing it, rather than spending big bucks on big bore kits, hot cams and headwork? Cheers, Terry.    

[seanbarney41]

Terry, 10hp is a lot when you are talking about maybe 60hp total...I would think that whole laundry list, real as it is, amounted to about 3 or 4 hp....but out of 60 that is noticeable...

[Terry in Australia]

Yeah mate, I could believe a figure of under 5 BHP for the "laundry list" of modifications during the CB750's lifetime, but when folks start talking 10, I get a tad skeptical. I've owned just about every model CB750 over the last 34 years, (and often several 750's at the same time) and apart from my K0 and F2, they all pretty much felt the same. Cheers, Terry.