Topic: big bore kit

[ntintruder]

I need some recommendations from anyone with knowledge about big bore kits that would work with a 1977 (the black engine if that makes any difference).

[Tintop]

How big do you want to go??  If over 1000cc MikeR's billet block solution.

[Jerry Rxman Griffin aka MuthaF'er]

The "black engine", if a 77/78F engine, needs different type of domed pistons than all the others due to the head differences so be specific to that. Perhaps CycleX or Dynoman? 

[dragracer]

Look for the number at the rear of the head. It will be 410 if it's the big valve F2 head. As Jerry stated, you will need pistons specifically for the F2 head. I believe the biggest off the shelf pistons available are 970. Both dynoman and cycle ex carry them.

[scottly]

Whoa guys, 900+ cc motors get expensive in a BIG hurry.   To the OP, the most common big bore kit for 750s is 836cc, or 65mm, which is a 4mm over-bore from the stock 736cc 61mm.

[seanbarney41]

A.p.e. has stuff too...specific to f2/3

[PeWe]

836 cc does not need stronger rods.
The head might need a restore with new guides and valves.
A cam with good response from low if this is a street bike. DP295  from Dynoman.
This make the bike a lot stronger than stock.
Engine might need a general overhaul with new chains and tensioners.

[ntintruder]

Thanks guys

[gschuld]

Ntintruder,

Could you give us an idea regarding your performance goals and general budget.

We are great at theoretically spending your money if left to our own devices😁

George

[PeWe]

If going 1000cc, Mike's billet block. APE Ultra crank with Carillo rods, ported head, lightened alternator,  undercutted trans. Better carbs like Mikuni TMR 32 or RS34.
Just contact Mike he might have most in stock and can arrange everything else
Forum profile MRieck

The torque of such engine is fantastic!

[ntintruder]

 I was thinking of spending maybe a grand to get 836cc I don't want to get into connecting rods. but I might consider a different cam.

[gschuld]

Oh, you are one of those sane types🤔

No room for that on this board😂

Seriously, that’s a very cost effective way to go.

George

[PeWe]

That's how it starts, 836, good head maybe ported and a good cam not too hot high revving.
It's a pity that Action Fours cams are no longer available. I used Their SS-1 in the 80's with good response and good idle, perfect touring bike. Later measured on dyno 80 whp with better carbs, F2 inlet valves.
RC295 cam gave a little bit more torque from 3500rpm, no dyno.

[RAFster122s]

Gasket set
Pucks for head
Cam chain
Adjustable cam chain sprocket to degree in the new cam
Degree wheel unless you make one or buy one or borrow one
Tensioner and slipper blades
Primary chain if the motor has a lot of miles on it
836 piston kit
Seals for motor and output shafts in case
Plastigauge for measuring bearing clearance
Possibly need new tranny bearings
New valve guides and possibly a valve or two as required if any are worn badly
Paint for motor
New sprockets and chain
All balls tapered neck bearing kit for the steering neck
New wheel bearings
Possibly new cush drive rubbers depending upon condition of those in your rear wheel
Primary drive cush rubbers if yours are worn
Head porting work, valve guide replacement, head rebuild
New cam

Yeah, you would be lucky to do that for $1000, I would plan to spend $2000 or more

How many miles does the motor have on it?

David

[PeWe]

Only a good ported head is $2000, probably more
I'm sure most old heads need new ex guides + valves.

Cheap Cruzinimage 836 kit + webcam 41 + restore head (guides and valves) and all above parts needed when restoring the engine will exceed $1000 US.

$10.000 on engine only easy done

[RAFster122s]

Only a good ported head is $2000, probably more
I'm sure most old heads need new ex guides + valves.

Cheap Cruzinimage 836 kit + webcam 41 + restore head (guides and valves) and all above parts needed when restoring the engine will exceed $1000 US.

$10.000 on engine only easy done

PeWe, yeah, I was trying to let him down easy... A good port job is worth the money invested...but that said...lots of late 80s bikes will out perform the bike after the expenses of the rebuild and port job.
So, like Clint Eastwood says, A man’s gotta know his limitations,  or in this case: the bike’s.


Bore job can be $100/hole at some shops for an over bore...


You need to be realistic in your expectations for the bike and the expenses of rebuilding a motor.  Cutting corners can often bite you in the tush...


so, sit down with a computer file and price your project and then decide if you want to marry the bike to make that investment.


Much of a bike’s value is determined by its cosmetic condition...so, what does the rest of the bike look like?


Then you need to insure it for its condition given you rebuild the motor and clean up the cosmetics.  Now if you go down the road of repaint the bike starts to be pretty expensive...


Yep, old bikes can be fun but you can get carried away and spend a fortune on one.  It gets even more expensive when you start a project and then do not have the money to finish it and you have a huge loss when you get rid of it because you cannot finish it. So, plan ahead and save for the project before you start it.


David

[PeWe]

It must be tons of ported heads from the 70-80's out there to be used again. A valve-guide job for not that much money.

I found one old ported head for $125, had to invest another $800 at my local tuning shop to make the ports beautiful, increase inlet ports so my not much used F2 inlet valves with lash caps can be used. Almost new ex valves too.
Cost of the valves to be added.

My initial plan was to use the head as it was, stock valves to be lapped.
This head saved as spare if my ported K6 head with 5mm valve kit 34/28 will give up.

[ntintruder]

 the  $1000 was just what I was budgeting for the big bore kit. the engine has 42000 miles on it I did one big bore kit on a CB750 20 years ago but I haven't looked at prices or manufacturers since as I have been playing with GL1000s for a while, quite a while actually, but now I think I want to get back to the inline fours so I bought this f model, runs very well. If I decide to go ahead with the project I know I will be spending more than a grand .

[scottly]

It's known as Falling down the rabbit hole.

[PeWe]

It is fun to modify followed by  test rides.
10.5:1 pistons can start a domino effect with a cam with more overlap than stock, springs and head job. The good JE pistons have thin oil rails that need careful assembly of the cylinder.

[scottly]

head job.

A head job is always good. Seriously, a good head may be worth as much HP as an 836 kit?

[PeWe]

A head job seems to always be needed on a CB750.
I found a really good looking K6 head on eBay USA. All threads OK. Inlet valves and seats looked as new while ex valves were really bad, ex guides really worn.
I let my local shop clean  chambers, replace ex guides with stock Honda valves and mount almost new ex valves I had.

A stock bike need head fixed anyway.
If bike has been standing still for years, I bet the seats and valves are pitted  in need of valve job (cutting seats, lapping plus new seals).

[RAFster122s]

High compression is another tasty treat in a motor that is best served with a good ported head.

Displacement is nice but displacement without a bump in compression only taps into a piece of what is possible.

 (High compression bites you in the buttocks when that compression only allows you to use race gas [unless of course it is a race bike] or it causes detonation and pinging problems during hot weather.)

But, it is all a question of what your goal for the bike is...