Topic: Edit: Decided to Rebuild The Top End of other K4 (instead of repair trans)

[Drew75]

Seemed fine on the center stand... under load it pops out of second. Grindy too.

Any ideas?

[ekpent]

Is it a 750?If it is probably a bent or broke shift fork or broken-bad dog on the gear.I have a spare motor to fix with the same problem-you will need to split the case

[Drew75]

That's what my mechanic said - he's going to do it for $500 including parts and have it to me in one week.

What do y'all think?

Took her for her first ride today, sans not having second gear she sounded and handled great - stupid second gear...

[1timduke]

Make sure you do a compression check on the bike before he breaks it down, also ride a little and check for oil leaks.   Be a shame to get it back together and realize you got poor compression and need top end work as well.

I'm not really sure about the labor/parts cost, is he getting 'new' parts?

-Tim

[grumpy]

I feel your pain.
Mine pops out of fourth. I'm short shifting 3rd until rebuild season.
I have a spare tranny ready & waiting for winter.

[B.O.X.N.I.F.E.]

Read this:

http://forums.sohc4.net/index.php?topic=44816.0

Claims you can do this without fully splitting the cases. I'm tempted. Opinions?

[bryanj]

Depends on year and model and bike but selector drums wear as well

[Drew75]

Depends on year and model and bike but selector drums wear as well

1974 CB 750 23K

I'm not really sure about the labor/parts cost, is he getting 'new' parts?

From what I understand we are going with used parts - he has several donor engines to pick and pull from - and a one week turn-around to boot.

Be a shame to get it back together and realize you got poor compression and need top end work as well.

Regarding compression this is where we were prior to the carb rebuild:

# 1 115 psi
# 2 140 psi
# 3 160 psi
# 4 140 psi

How does that strike you gentlemen?

Very little white smoke after sitting for two years - stops once the bike is warm, very little on acceleration. Engine sounds smooth and an occasional blub or quiet pop from the exhaust.

The only leak is from the oil pressure gauge - just needs to be tightened.

[MCRider]

Depends on year and model and bike but selector drums wear as well

1974 CB 750 23K

I'm not really sure about the labor/parts cost, is he getting 'new' parts?

From what I understand we are going with used parts - he has several donor engines to pick and pull from - and a one week turn-around to boot.

Be a shame to get it back together and realize you got poor compression and need top end work as well.

Regarding compression this is where we were prior to the carb rebuild:

# 1 115 psi
# 2 140 psi
# 3 160 psi
# 4 140 psi

How does that strike you gentlemen?

Very little white smoke after sitting for two years - stops once the bike is warm, very little on acceleration. Engine sounds smooth and an occasional blub or quiet pop from the exhaust.

The only leak is from the oil pressure gauge - just needs to be tightened.

A shift drum is a possibility, but 99% of the time its a bent shift fork. Used is OK if it's not bent. You can tell visually as a bent one will have a circular wear mark on it where the gear has worn a groove as it spins against the shift fork blades. If there is no wear mark, 99% of the time its not bent, or not bent enough to matter.

Bending a shift fork comes from abuse 99% of the time, powershifting into 2nd and not completing the shift, usually resulting in over-reving, which usually won't damage anything on a stock motor as the valves just float. On a built motor, one could bend a valve.

(I classify "abuse" 2 ways, benign and malicious. Benign is when someone is just trying to go fast and made a mistake. Malicious is when someone is just a jerk, not paying attention, doesn't know what they are trying to do and generally beating the bike up. Based on the condition of the bike in your picture, its probably benign, hoping there isn't a lot of ancillary damage.)

Compression in #1 is too low, but rideable. Could possibly be a very slightly bent valve. 140 to 160 is at the low end to middle of normal. Makes #1 suspicious as its the odd man out.

If it were rings, they usually wear more evenly, so all 4 would be between 140-160. A bent or leaking valve could be one cylinder only.

[Drew75]

Thank you MC, so should we go ahead and have a look at cylinder #1?

I'm already spending $500 for the transmission work - should I just pony up to handle the compression issue?

 ...and what do you think a fair price to fix would be?

thanks again!

[MCRider]

Thank you MC, so should we go ahead and have a look at cylinder #1?

I'm already spending $500 for the transmission work - should I just pony up to handle the compression issue?

 ...and what do you think a fair price to fix would be?

thanks again!

Terry from Aust has a good protocol for testing valve leak vs ring leak, I'll copy you on it as soon as I'm done here. A big part of the $500 is pulling the engine. So likely now is the time to address it all.

With the head off, assuming its a valve, easy to replace one valve, lap them all in, and screw it back together. Don't get carried away with an all out valve job unles you just have $$ burning a hole...

A couple of extra steps if you need to pull the cylinders and re-ring it. de-carb the pistons, hone the cylinders, etc. Don't get carried away with boring, new pistons, etc, unless...

The easy path shouldn't be more than $125 for head only, $250 for head and re-ring. Plus or minus...

It'd be sweet after all that (the easy path). The extra $$ path is sweeter, but unnecessary.

[Drew75]

Thank you so much man - I love my stupid bike and now I'm addicted to getting her right.

So $500 to fix the trans and another $125 + $250 for the engine work - not bad. I'm doing it.

 

[MCRider]

Thank you so much man - I love my stupid bike and now I'm addicted to getting her right.

So $500 to fix the trans and another $125 + $250 for the engine work - not bad. I'm doing it.

 

What Terry has said is essentially: (paraphrase) "do your compression test as you have. Now put a little oil in each cylinder (or the offending cylinder), do the test again. If the offending cylinder improves its likely the rings. If it doesn't improve, its likely a valve. Either a simple leak, or its bent (which would cause it to leak). If it is bent that seat may need to be cut to freshen it up, while the others will respond to a simple "lapping in".

The bent valve would have come from its kissing the piston when the PO missed the shift that bent the fork, and the engine over revved. The engine would still run, but might pop and/or gurgle. It could just be that the valves in #1 got burned from being too tight, a sloppy tune up,  and are leaking. An aggressive lapping will often fix that.

Good luck!

[B.O.X.N.I.F.E.]

Depends on year and model and bike but selector drums wear as well

Once you get the clips out of the forks shouldn't the drum slide out? The way I read the article is sounded like the entire trans assembly would come out, is that not right?

[Drew75]

Fellas -

I'm now being told if we are going to pull the top end it's just makes sense to go up to an 836 cc engine - can I just buy one out of the crate?

Also what would be standard charge to do this?

[MCRider]

Fellas -

I'm now being told if we are going to pull the top end it's just makes sense to go up to an 836 cc engine - can I just buy one out of the crate?

Also what would be standard charge to do this?

Re-read my post and think about keeping it simple. If it wasn't your idea in the first place to go to an 836cc, maybe shouldn't do it. You'll be opening a can of worms (and your checkbook) to a tune you weren't ready to play, a project that just never ends, and more complications. Its tempting for sure. Resisting temptation is sometimes the way to go.

A simple finely done lap job and re ring job will give you a sweetheart engine and no pain. Spend any extra money on brakes, suspension, riding gear, tires, and training. You'll be way better off.

PS: I'm saying this assuming you are relatively new to the sport, and to mechanical improvements and modifications? keep that in mind.  But there have been many times in the past I wished I'd heeded this advice and others on the forum have told me the same.

[Patrick]

It may make sense to go 836 if you are the guy charging, not paying. Add at least $250 for the big bore kit, another $60 per hole for the bore job and the labor and you've easily added some serious change to your rebuild.

It's really a question of how much you want to spend for the $500 transmission.

[Drew75]

Sorry, to clarify this is what he said:

Step one he cracks the case and has a look - for $500 he fixes the 2nd gear shift problem - the bike is ridable.

While I'm riding the bike albeit not at full compression I still have a bike and he begins work on a 836 engine he already has in his shop.

I pay half up front and half upon completion. Question is what is a fair price for an 836 rebuild and if I go with a simple lap job and re ring job how much should I be charged?

Thanks again everyone - and yes, sans my 07' Bonnie I have little experience with bikes mechanical or otherwise.

(keep in mind this guy has been working on these bikes since '75, ran the Honda Service Dept here locally and raced them)

[MCRider]

Sorry, to clarify this is what he said:

Step one he cracks the case and has a look - for $500 he fixes the 2nd gear shift problem - the bike is ridable.

While I'm riding the bike albeit not at full compression I still have a bike and he begins work on a 836 engine he already has in his shop.

I pay half up front and half upon completion. Question is what is a fair price for an 836 rebuild and if I go with a simple lap job and re ring job how much should I be charged?

Thanks again everyone - and yes, sans my 07' Bonnie I have little experience with bikes mechanical or otherwise.

(keep in mind this guy has been working on these bikes since '75, ran the Honda Service Dept here locally and raced them)

Really throwing some curve balls now.  

So, you'll swap engines at the end? Yours for the bench engine? So you don't need to do the top end job (valves and rings) on yours?

You've got quite a range on the price of the 836 cc piston kit, probably $250 to $500. Brand, forged (expensive, lighter, stronger) vs cast (standard technology, heavier, cheaper, still fine to use though). As mentioned, $60 +/- to bore each hole (x4). Most of the rest is the same as the simple valve lap and re-ring. Say $250 in labor. The 836 is now the ring job. The valve lapping is the same either way.

[Patrick]

I don't think anyone can tell you in advance what a fair price would be for an 836 engine without more information. What Is the mechanic going to do to take advantage of the additional displacement? Will he put in new rods? Port the head? Aftermarket valves? New cam chain? New cam chain tensioners? It's like asking what is a fair price for a car without telling us the year, make and model.

I think you would attract more estimates if you find out exactly what the mechanic is going to do to the engine and how much he wants to charge for it and then ask if it's a fair price.

Patrick

[Drew75]

heh... sorry guys now I'm confused.  

My mechanic has an 836 engine that was built by one of his tech years ago - he would need to "get into it" and have a look but it's a complete 836 no mods needed.

He would begin the clean up and setup of that engine for me while I ride my bike with the current engine that has the aforementioned minor compression issues. Still sounds good, little to zero white smoke, the occaisional blub and faint pop from the engine.

He does the trans for $500 we skip the simple valve lap and re-ring and apply that $250 towards the 836 engine.

So if you had a complete 836 sitting in your shop and it needed some minor labor hours to setup what would you charge a shlubo like me?  

[Patrick]

Why pay $500 for the tranny job if you are going to replace the engine with the 836 anyway?

[Drew75]

Why pay $500 for the tranny job if you are going to replace the engine with the 836 anyway?

Well this bike has been 6 months in the making and I don't want to rush the 836 - it could be a month + before he completes it, I just assumed I could get the $500 back out of the current 750 K4 Engine when I sell it.

Basically it comes down to I want something to ride - he can have the trans fixed in one week. Then I ride the bike and don't rush the 836.

[Bill/BentON Racing]

Drew,your questions brought up some good answers,Patrick hit the nail on the head,we have many avenues we could go down,but anyone who has ever built motors will know you will not really KNOW until you get inside and assess the damages.You could spend a ton to build a proper 836cc engine,the one we talked about is a 1974 RC or Yosh,RC was forged,Yosh are cast,same people who did Honda pistons ART,
it does have Yosh alum rods,light but durable? I rather use steel rods,cast pistons fine,forged stronger but usually heavier.It should have cam from that era,KH,Engle,Yosh etc.As discussed with Drew any used engine is a gamble.Also we could use 1974 engine that just needs a headgasket,might be a better solution? No easy answers on this one but Bill has work to do.Anyone who has ever felt the difference between a PROPERLY built 836cc High Performance motor and stock knows the answer to what to do.The real question is how fast you want to ride and how fa$t do you want to go?Loved reading the responses keep up the good work!Thanks,Bill Benton
P.S. He just needs to get on a Honda 750 and it will all be good!Also I will try and update my profile.I am fortunate to have stuff from 69 sandcast cases to Tracy body to Rickman CR.Honda 1,2,3,4,and 6 cylinders live around here and one 1974 4 speed.Maybe we put Yosh CR trans in,just kidding.

[Drew75]

Hey! Cool! Everybody the guy above is my builder, all the great pics you see credit goes to him!

Thanks for dropping in Bill - looking forward to talking options tomorrow at the shop.

found some tank trim options:

http://forums.sohc4.net/index.php?topic=54725.0