Topic: Thinking I am going to do a complete engine build 78 cb750k

[Dime]

I am waiting for HondaMan's book to show up then I am thinking I am going to tear the engine down completely and rebuild the bottom end as well.

The reason being is that I trust nothing with this bike. Everything I am finding so far has been a result of neglect and poor maintenance.

This is already a long term project. When it is done I don't want to have to worry about it for awhile. I know if I leave the bottom end I will always be worried about it.

Again waiting for the book for some guidance but I plan on riding this bike hard. Not racing necessarily but definitely putting it though it's paces.

I want to use every trick in the book, so to speak, without getting into racing parts like lightened crank and aftermarket rods.

I plan on running either dohc pistons or the cruzinimage 836cc kit. HD cylinder studs and most likely a cx-1 cam. Head will be rebuilt with some porting as well.

I want to build an old hot rodders engine. Relatively low buck but spending it in the right places. Not looking for max performance, just dependable fun factor.

Let me know your thoughts. I have no experience with the cb750 sohc engine. This is all a learning experience for me. Just want to do it right once and be good for the foreseeable future.

Best regards,

Dime

[M 750K6]

This might be controversial.

In my humble view, a healthy stock 750 motor is matched fairly well with the rest of the bike. If you significantly up-rate the motor, I can't see how you'll enjoy it without addressing the chassis design, weight, suspension and brakes. At which point you will probably have a better performing bike, but you'll no longer have a Honda CB750.

I'll get my coat...

[Dime]

This might be controversial.

In my humble view, a healthy stock 750 motor is matched fairly well with the rest of the bike. If you significantly up-rate the motor, I can't see how you'll enjoy it without addressing the chassis design, weight, suspension and brakes. At which point you will probably have a better performing bike, but you'll no longer have a Honda CB750.

I'll get my coat...

I can appreciate your point but like anything a platform can take on many different characteristics. A well designed cb750 chopper would still benefit from a modified engine.

I already have in the works changes to the suspension including new front end as well as progressive suspension out back. The brakes will be upgraded as well. I see no reason to modify the frame however. I still consider the meat and potatoes of the cb750 sohc to be intact.

[Stev-o]

What is the history of the bike, have you ridden it? Mileage??

The bottom end of the SOHC bike is nearly bulletproof, I've never considered having to rebuild one, even on one that had 60K miles.  It will be very pricey.

The top end is where you want to spend your money. It had been my experience that a good valve job is worth it's weight in gold.  Cruzen image pistons get good reviews but I used Wiseco's in my K4 836.

[Dime]

What is the history of the bike, have you ridden it? Mileage??

The bottom end of the SOHC bike is nearly bulletproof, I've never considered having to rebuild one, even on one that had 60K miles.  It will be very pricey.

The top end is where you want to spend your money. It had been my experience that a good valve job is worth it's weight in gold.  Cruzen image pistons get good reviews but I used Wiseco's in my K4 836.

No I never even got to ride it. The compression was low, turns out scuffed pistons on all four. From the state of the work done on the bike in general I would say it was fairly neglected. It did run but very poorly, last going off cylinder 1 would not run even with spark and fuel. At that point I decided to tear it down.

The cost of doing the bottom end is definitely daunting, especially if I go with the cycle x tensioners for primary and cam. Plus all new HD chains. It would be a solid unit after that though.

The whole point of this build is to not have any compromises. Every bike I have ever built I compromised due to finances. This time around I would rather take 5 years to build it than have one area that I am not sure about. That being said the cycle x tensioners are probably overkill. So can most likely save some there.

Hope that makes sense.

[Dime]

What is the history of the bike, have you ridden it? Mileage??

The bottom end of the SOHC bike is nearly bulletproof, I've never considered having to rebuild one, even on one that had 60K miles.  It will be very pricey.

The top end is where you want to spend your money. It had been my experience that a good valve job is worth it's weight in gold.  Cruzen image pistons get good reviews but I used Wiseco's in my K4 836.

No I never even got to ride it. The compression was low, turns out scuffed pistons on all four. From the state of the work done on the bike in general I would say it was fairly neglected. It did run but very poorly, last going off cylinder 1 would not run even with spark and fuel. At that point I decided to tear it down.

The cost of doing the bottom end is definitely daunting, especially if I go with the cycle x tensioners for primary and cam. Plus all new HD chains. It would be a solid unit after that though.

The whole point of this build is to not have any compromises. Every bike I have ever built I compromised due to finances. This time around I would rather take 5 years to build it than have one area that I am not sure about. That being said the cycle x tensioners are probably overkill. So can most likely save some there.

Hope that makes sense.

Sorry 23,000 kms

[andy750]

What is the history of the bike, have you ridden it? Mileage??

The bottom end of the SOHC bike is nearly bulletproof, I've never considered having to rebuild one, even on one that had 60K miles.  It will be very pricey.

The top end is where you want to spend your money. It had been my experience that a good valve job is worth it's weight in gold.  Cruzen image pistons get good reviews but I used Wiseco's in my K4 836.

Stev-o unfortunately thats not been my experience re: bottom end. Had my K2 bottom end done in 2004 due to bearing failure (50,000 miles) and the K4 had a complete bottom rebuild at 90,000 miles or so.

CB750K2 with wiseco 810cc pistons
Bottom end rebuild
Dynoman 295 cam
New valves/honda valve guides
New rocker arms
Jetting - 40/120
Exhaust - HM300s
Air filter  - stock airbox with K&N filter
Tires - Avon Roadriders
Chain -RK O-ring 102 links
Sprockets - 17/48 (Z1 enterprises)
Ignition - Dyna S
Coils - stock
Plugs - Denso Iridiums
Suspension (rear) - Hyperpro
Suspension front: Sonic straight springs
Dynoed at 74hp
recorded by GPS - 104 mph at indicated 6800 rpm (was pretty stable) in top gear (done on a closed course since I dont condone speeding on public roads as that would be irresponsible  ).

[Dime]

What is the history of the bike, have you ridden it? Mileage??

The bottom end of the SOHC bike is nearly bulletproof, I've never considered having to rebuild one, even on one that had 60K miles.  It will be very pricey.

The top end is where you want to spend your money. It had been my experience that a good valve job is worth it's weight in gold.  Cruzen image pistons get good reviews but I used Wiseco's in my K4 836.

Stev-o unfortunately thats not been my experience re: bottom end. Had my K2 bottom end done in 2004 due to bearing failure (50,000 miles) and the K4 had a complete bottom rebuild at 90,000 miles or so.

CB750K2 with wiseco 810cc pistons
Bottom end rebuild
Dynoman 295 cam
New valves/honda valve guides
New rocker arms
Jetting - 40/120
Exhaust - HM300s
Air filter  - stock airbox with K&N filter
Tires - Avon Roadriders
Chain -RK O-ring 102 links
Sprockets - 17/48 (Z1 enterprises)
Ignition - Dyna S
Coils - stock
Plugs - Denso Iridiums
Suspension (rear) - Hyperpro
Suspension front: Sonic straight springs
Dynoed at 74hp
recorded by GPS - 104 mph at indicated 6800 rpm (was pretty stable) in top gear (done on a closed course since I dont condone speeding on public roads as that would be irresponsible  ).

When you did the bottom end did you use Honda style tensioners? I am assuming you used HD chains for the primary and cam? Thank you

[MauiK3]

Check Yamiya for parts like cam chains and tensioner parts. The stock stuff is very good.
I'd suggest inspecting and measuring the bottom end before assuming you need new bearings etc.

[Dime]

Check Yamiya for parts like cam chains and tensioner parts. The stock stuff is very good.
I'd suggest inspecting and measuring the bottom end before assuming you need new bearings etc.

I sold my mics years ago when I gave up building engines full time. So I will be buying a couple mics or having my old boss mic it for me. Either way everything will definitely be measured before I go buying new bearings shells. I am just hoping that the apparent lack of oil changes and maintenance isn't going to bite me.

[Dime]

Check Yamiya for parts like cam chains and tensioner parts. The stock stuff is very good.
I'd suggest inspecting and measuring the bottom end before assuming you need new bearings etc.

I haven't seen the condition of the primary tensioner but the cam tensioner and wheels are in good shape just hard.

I have no issue using stock parts if it will hold up to aggressive riding. Again not racing but definitely putting through paces.

[andy750]

What is the history of the bike, have you ridden it? Mileage??

The bottom end of the SOHC bike is nearly bulletproof, I've never considered having to rebuild one, even on one that had 60K miles.  It will be very pricey.

The top end is where you want to spend your money. It had been my experience that a good valve job is worth it's weight in gold.  Cruzen image pistons get good reviews but I used Wiseco's in my K4 836.

Stev-o unfortunately thats not been my experience re: bottom end. Had my K2 bottom end done in 2004 due to bearing failure (50,000 miles) and the K4 had a complete bottom rebuild at 90,000 miles or so.

CB750K2 with wiseco 810cc pistons
Bottom end rebuild
Dynoman 295 cam
New valves/honda valve guides
New rocker arms
Jetting - 40/120
Exhaust - HM300s
Air filter  - stock airbox with K&N filter
Tires - Avon Roadriders
Chain -RK O-ring 102 links
Sprockets - 17/48 (Z1 enterprises)
Ignition - Dyna S
Coils - stock
Plugs - Denso Iridiums
Suspension (rear) - Hyperpro
Suspension front: Sonic straight springs
Dynoed at 74hp
recorded by GPS - 104 mph at indicated 6800 rpm (was pretty stable) in top gear (done on a closed course since I dont condone speeding on public roads as that would be irresponsible  ).

When you did the bottom end did you use Honda style tensioners? I am assuming you used HD chains for the primary and cam? Thank you

Yes OEM tensioners and HD chains for both primary and cam

[Dime]

What is the history of the bike, have you ridden it? Mileage??

The bottom end of the SOHC bike is nearly bulletproof, I've never considered having to rebuild one, even on one that had 60K miles.  It will be very pricey.

The top end is where you want to spend your money. It had been my experience that a good valve job is worth it's weight in gold.  Cruzen image pistons get good reviews but I used Wiseco's in my K4 836.

Stev-o unfortunately thats not been my experience re: bottom end. Had my K2 bottom end done in 2004 due to bearing failure (50,000 miles) and the K4 had a complete bottom rebuild at 90,000 miles or so.

CB750K2 with wiseco 810cc pistons
Bottom end rebuild
Dynoman 295 cam
New valves/honda valve guides
New rocker arms
Jetting - 40/120
Exhaust - HM300s
Air filter  - stock airbox with K&N filter
Tires - Avon Roadriders
Chain -RK O-ring 102 links
Sprockets - 17/48 (Z1 enterprises)
Ignition - Dyna S
Coils - stock
Plugs - Denso Iridiums
Suspension (rear) - Hyperpro
Suspension front: Sonic straight springs
Dynoed at 74hp
recorded by GPS - 104 mph at indicated 6800 rpm (was pretty stable) in top gear (done on a closed course since I dont condone speeding on public roads as that would be irresponsible  ).

When you did the bottom end did you use Honda style tensioners? I am assuming you used HD chains for the primary and cam? Thank you

Yes OEM tensioners and HD chains for both primary and cam

Right on thank you

[RAFster122s]

Kawasaki chains are cheaper and direct fit and meet or exceed original items.

[Dime]

Kawasaki chains are cheaper and direct fit and meet or exceed original items.

Interesting. Don't happen to have part numbers would you?

[bryanj]

The Kwak chain is the hyvo for the 500/550 that is less than half Honda price

[Dime]

The Kwak chain is the hyvo for the 500/550 that is less than half Honda price

That is awesome! Thank you

[RAFster122s]

Sorry didn't realize it was 550/500 fitment and not 750

[Dime]

No worries. I miss understood him.

Apparently the automatic cb750 use the hyvo chains but they are not any stronger than the HD chains you can get. The cost is definitely a factor but I plan on doing this once for the foreseeable future.

[PeWe]

CB750 chains.
I used timing chains for cars in my CB750 K2 build. 68 links, no need to cut and rivet.
Slack after ca 16500 km 65.45mm. I think it was closer to 65.0mm when installed.
That chain look like CycleX heavy duty chain. Links with holes...

BMW 530 d,  184 HP,  [E39],  Production: 1998/08 - 2000/09,  Engine code: M57 D30 (306D1)
Original partno: 11 31 2 248 729

You can find more about prim chains in this thread.
http://forums.sohc4.net/index.php/topic,154183.100.html

My blue K6 has the German eBay shop Classic Cycle City  Heavy Duty chains.
It has not stretched much  during 55.000 km. Recent check showed 65.5mm slack. It was just under 65.0mm when installed.

The first 6000km 836cc with 80whp DIN, followed by ca 20.000 km 1005cc  90whp-100whp. After that 105whp rest of the distance.
Last 25.000 km 970cc with thinner base and head gaskets that gave higher compression and a few hp more. Top power 107.5 whp.
Primary chains does not bother. Stock tensioners.
Street use but at least 10-12 torturing dyno visits with 3-4 full  runs each time.


Cam chains have recently been discussed  in another thread.

DID 219FTH a durable chain for not much money if finding the right seller.
I think I paid ca 30-40 Euro each a few years ago.

I think it is like the famous Tsubaki Camilla chain.
Here photo of both I have.
Tsubaki vs DID219FTH side by side

[Dime]

CB750 chains.
I used timing chains for cars in my CB750 K2 build. 68 links, no need to cut and rivet.
Slack after ca 16500 km 65.45mm. I think it was closer to 65.0mm when installed.
That chain look like CycleX heavy duty chain. Links with holes...

BMW 530 d,  184 HP,  [E39],  Production: 1998/08 - 2000/09,  Engine code: M57 D30 (306D1)
Original partno: 11 31 2 248 729

You can find more about prim chains in this thread.
http://forums.sohc4.net/index.php/topic,154183.100.html

My blue K6 has the German eBay shop Classic Cycle City  Heavy Duty chains.
It has not stretched much  during 55.000 km. Recent check showed 65.5mm slack. It was just under 65.0mm when installed.

The first 6000km 836cc with 80whp DIN, followed by ca 20.000 km 1005cc  90whp-100whp. After that 105whp rest of the distance.
Last 25.000 km 970cc with thinner base and head gaskets that gave higher compression and a few hp more. Top power 107.5 whp.
Primary chains does not bother. Stock tensioners.
Street use but at least 10-12 torturing dyno visits with 3-4 full  runs each time.


Cam chains have recently been discussed  in another thread.

DID 219FTH a durable chain for not much money if finding the right seller.
I think I paid ca 30-40 Euro each a few years ago.

I think it is like the famous Tsubaki Camilla chain.
Here photo of both I have.
Tsubaki vs DID219FTH side by side

This is a great post and much appreciated.

I have no problem going with the G67HP-6 primary chains. Just need to find a supplier.

As for the cam chain that looks great. Will source that as well.

Everything is on the back burner right now as money got really tight. But will source the parts and have them ready when things get more fluid. I have already committed to two purchases but that is it.

So is life.

[Geoff Hastings]

Although the engine is regarded as fairly bullet proof the bike I bought had dodged the bullets but not the neglect and abuse. One piston was broken and the main bearings shot. This was all the result of missing oil changes and never cleaning the oil strainer which was totally blocked. Luckily the bores were still great and the crank journals perfect but once you start to add up the costs of the mains, big ends, chains tensioners etc the costs run away. I did end up rebuilding the engine and it does run sweet now but it was touch and go as to wether it would be worth it.

[Dime]

Although the engine is regarded as fairly bullet proof the bike I bought had dodged the bullets but not the neglect and abuse. One piston was broken and the main bearings shot. This was all the result of missing oil changes and never cleaning the oil strainer which was totally blocked. Luckily the bores were still great and the crank journals perfect but once you start to add up the costs of the mains, big ends, chains tensioners etc the costs run away. I did end up rebuilding the engine and it does run sweet now but it was touch and go as to wether it would be worth it.

Thanks for your reply.

Realistically speaking this will most likely be my last bike. My back, knee, shoulders and elbows are all giving out.

I want it to be exactly how I want it, including the engine. Money wise it may not be worth it to some. To me, I have wanted a cb750 sohc for almost 20 years.

When it is done I am going to enjoy whatever time I got riding left on this Honda.

Probably not doing anything performance wise to it. Just longevity wise.

[Don R]

 In the end, it's what you're comfortable with that matters. I did a quickie hone and rings on my old Rat Race RC-836 engine but here I am the next year planning to rebuild it to replace the noisy chains. Give the oil pump a seal kit while you're in there.

[Dime]

In the end, it's what you're comfortable with that matters. I did a quickie hone and rings on my old Rat Race RC-836 engine but here I am the next year planning to rebuild it to replace the noisy chains. Give the oil pump a seal kit while you're in there.

I am definitely going to do the chains. I just don't think I am going to opt for the cycle x tensioners.

PEWE provided some great info on the primary chain options as well as a cam chain.

I think plenty of others are using the stock type tensioners with good success.

Haven't skipped ahead in Mark's book to see what he does. Probably do that tomorrow.

I am not going performance build with this anymore. It will possibly get bored to 65mm but remain with stock cam. I already have the 5 ohm dyna style coils as well as the dyna style electronic ignition.

The head will be rebuilt so that, combined with a fresh bottom and top end should make for a solid runner.

Shouldn't break the bank either