Topic: CB750K6 -76 project back to life with more updates

[PeWe]

Done 12  inserts today. Threads for valve cover look good.

I'll do a test mounting valve cover, tighten 8Nm.

Drilled the tight oil feed holes.
They were only 8.5mm, HD cyl studs are 8.0mm. Not much space for oil.

Stock studs are slimmer, 6mm no problem then.

9.5mm drill solved the flow question.

[PeWe]

One step further and keeping this thread within easy reach.

No inside harmed when painting.
An extra valve cover dressed in alu foil protected.

[PeWe]

Head finally assembled and torqued. 25Nm (18.44 ft-lb)
Later found 25Nm not enough for MLS to seal, 20-22 ft lb.

Before that.
Test mounted valve cover and had to shorten 10 M6 that were 65mm long. Honda say a few mm less.
4 of them bottomed out before tightened so I had to grind all 10 to 62-63 mm, fix the ends with a threading tool.
Tightened with 7.5Nm. all threads good, no need of thread repair.

Mounted spark plugs. Chosed those that got its electrode gap facing towards In valve. I had to test closer to 15 plugs until I found an OK oriented for cyl 2.
Marked all plugs 1-4 and removed them.

Again same bad surprise when mounting the head!!
The opening for the longer version of cam chain slider did not fit. Head off and filed the opening so head could go on.

I was sure that later heads had the longer version of slide. This head marked 392.
My K2 got a K6 head that had same issue. Also a late surprise.

Head finally on. Will retighten it again tomorrow.

[PeWe]

I got a 2nd thought about the reused MLS headgasket after a quick compression test that showed lower compression and too much difference between cylinders despite all 4 chambers are really equal and not larger than previous head.
Latest head 23.6cc, earlier 23.7/23.8cc that gad 197.5-202.5 PSI with thicker base gasket.
I expected more, all around 200-205PSI.

Pistons around CR 11:1 with 22.5cc chambers
I have measured several times and compared with old (100whp head).

Same cam 1 degree earlier.

Thinner base gasket should crank up compression too. Reduce total chamber size by 1cc.


Head off and new MLS gasket(s),  ordered. (Fiber too just for sure and ev. future fixes)
Dynoman Texas.
I do not know any closer for MLS 72mm

Did the wheels. Late surprise, 3 spoke nipples short on rear wheel. Contacted seller that responded direct to ship missing nipples.
I can do the front wheel.

Tighten, truing and mount the 90/90-19 tire. Can mount it on bike too.

[MauiK3]

What rims are they, look nice!

[PeWe]

Non-valanced alloy rims from Central Wheel UK.
Stainless steel spokes.

I sent them a mail and got the alternatives. Valanced or non- valanced and sizes.

I asked for 2.15-19 front for wider tire than stock 3.25.
2.75-18 for 120/90 rear.
No 2.75 available, 2.5 and 3.0 OK.

3.0 will look nice.
I'll start with the 120/90 I fitted bikes stock wheel this winter. I'll see how it will wear on a better matched rim than stock.

After that a better looking and probably better matching 120/80-18 I have. Also Metzeler Roadtec 0.
Tire diameter very close to stock with 4.0-18

[BenelliSEI]

Nice set of wheels.

[SOHC4 Cafe Racer Fan]

Great looking wheels.

[PeWe]

Thanks guys!

I look forward to take photos with the wheels on and bike really clean. Frame parts need a good clean and a wax.

[PeWe]

Truing the wheel took some time.
Garage job moved into the living room.
Tire on tomorrow after tire irons have been grinded smoother.

[andy750]

Hey Per looking for your expert opinion on tires for my K2 - Buchanan spokes and Sun rims. Already have used Bridgestone BT-45s for years and looking for something different. Ill keep the front a 100-90-19 but the rear rim is wider and can take a 120-80-18. Any suggestions for good cornering, good in wet/dry and good for grooved pavement.

Thanks
Andy

[PeWe]

Hi Andy,
I happen to have a 120/80-18 tire I'll use.
Metzeler Roadtec O1.
I have used one in size 4.0-18.

Dual compound with good grip and last longer. I like it.

I have not decided yet if my new rear wheel will get the 120/90-18 first or the 120/80-18.

[PeWe]

Front wheel got its tire today.
Metzeler Roadtec 01 90/90-19.

Surprise when I measured the width with a caliper. Slimmer than the 3.25-19 on stock rim bike has now!!
Old tire 0.5mm wider
(HEIDENAU K44 3.25-19)

I thought that the new 90/90 should be ~ 5mm wider.

Easier to get wheel into the fork then.
Except need of removing right caliper bracket.

Left caliper bracket must be off too.
The upper M6 threads need to be repaired.
Inserts and correct lenghts of M6. Not longer with Loctite as now which might be bad when brake is bending, bolt has not much support the first part... I have had thoughts about it when braking hard in higher speeds! 

Next is to fix caliper bracket threads and mount the wheel. Rear tire hopefully next weekend.

[andy750]

Thank you Per Ill need to look for those. Your front tire looks good - as always excellent photos.

Weather is getting warmer here so almost time to ride.

good luck!
Andy

[PeWe]

Photos with my phone. Possible to edit on phone and upload to site via Tapatalk.

Fun to do during a ride stop while the ride is ongoing!

[PeWe]

Thank you Per Ill need to look for those. Your front tire looks good - as always excellent photos.

Weather is getting warmer here so almost time to ride.

good luck!
Andy

Here photos for you Andy!
My 120/80 tire beside the 120/90 as I mounted on stock rim just to test if the dual compound make different wear on a too wide tire/ too slim rim.

I'll NOT remove the 120/90 from the stock rim and let the new wider wheel get it. My K2 need a new tire. Wheel swap.

[PeWe]

The new front wheel has entered the bike. Right side caliper close to spokes as before. Rear upper M6 bolt holding the right caliper bracket very close to rim and it had to be fiddled on as with stock wheel.

I hope I did not pinch the tube when tire went on. PITA to remove wheel and back on again.

The 90/90 tire look slimmer than it is   
I'll consider 100/90 next time.

EDIT: Measured the 90/90 tire. Real measure as the numbers.
Taped tire all around, off with tape which I measured to get the tires circumference.
Divided by PI (3.1415) to get the diameter.
 
3.25-19 tire does not differ that much, only 6mm higher than 90/90-19. 
Circumference differ 1.5% which means that speedo will show 1.5% more wirh the smaller 90/90.
For me +1.5kmh at 100kmh.

100/90-19 will be 10 mm higher than 90/90-19 and fill the gap to fender more.
(+4mm higher than 3.25-19)

[andy750]

Hi Per thank you for the photos very helpful as always. The 90-90 does look a bit skinny on the front. I have always gone with the 100-90-19 - no fit issues as long as front end is lifted up.

cheers
Andy

[PeWe]

3.25 look fatter on the 1.85" rim. 90/90 tire on 2.15" rim has only 0.5mm slimmer width if measure with a caliper.

The rim is wider, 2.15" inner size for tire which will affect the shape too.

It will be interesting to verify the handling. It look like a lower profile tire.

I'm most curious about the wider rear wheel with 120 tire and if it will wear well with handling OK until tire is worn out. 
On stock 2.15 rim not good.

[754]

Nice rims , remind me of Beemer rims but shinier.
 I ran a 70 or 80 profile  rear tire, dud not like it.. my engine revs too high before I did that,, dud not like the look either. Plus as pain to get on centerstand....keep a 20mm piece of wood around.

[PeWe]

Good input Frank!
I'll see how the 120/80 tire will affect gearing.
I have 17:48 which worked well with 4.0 tire. Felt better than 18:48.

The sprockets and chain are new so it's better to measure the   tires circumferences direct when I have done the rear wheel. Compare with wheel with worn 4.0 and another stock wheel with new 120/90-18.

This can be fed into the CB750 gearing Excel chart I found on this forum.

Maybe 18 front will return to match the tire. I have new 18t sprocket on the shelf.

[754]

Error , mine was a 70 series,  this bike revs real oh high .,irritating. 
 70 series mAkes it worse, and hard to get on stand.

[PeWe]

I have measured my tires circumferences (divided with PI to get the diameter the gearing chart use ).
New 4.0-18:          26.13"

New 120/80-18:   25.31"
Front  90/90-19    25.43"
Diff front-rear 0.12", 3mm almost same diameter.

If going up to 120/90 rear, follow up with 100/90-19 front.

Found that I need to replace the front sprocket from 17t --> 18t.
Checked with the Excel gearing chart.

17:48 worked really well with 4.0-18. All gears felt right, 2-5.

***According to the gearing chart on 5:th gear. ***
New 4.0-18 not mounted.
@ 4000rpm
17:48: 95kmh (59mph)
18:48: 100kmh (62mph)

New 120/80-18 not mounted.
@ 4000rpm
17:48: 92kmh  (57mph)
18:48: 97kmh. (60mph)

So with the 120/80, 18:48 will be rather close previous gearing.

Also possible to hit 220kmh!
219kmh @ 9000 rpm
17:48 only 206kmh at 9000 rpm.

I doubt that 9500rpm will happen on 5th gear.
17:48  218kmh  (135mph)
18:48. 231kmh  (143mph)

So, 18:48 is the way forward.
Front sprocket has to be lifted out from final shaft anyway when removing wheel.

Chain is riveted so that's the way to be able to lift chain off rear sprocket.

Good to know expected speed. 3.25-19 front wheel showed rather correct on my bike. Not much off.
I think 100kmh happened at 4250 rpm with 4.0-18, 17:48 which match the chart almost spot on.

I'll need to verify new front wheel that will show some extra since it is a little bit smaller.

I need to find the speedo warning signs measuring vehicles speed by laser of radar sometimes placed beside the road to make people to slow down. Often at 50kmh roads.

For me a perfect opportunity to check speedometer, just hit it!
Better resolution at 100kmh, see what speedo show, the diff is the percentage wrong.

I have a GPS too. Fasten it with tape.

[johno]

Per I look forward to your postings 
Your level of power and tuning is almost wasted on the road, maybe time to build a race bike and put a small jockey on, you would be a good crew chief, wear a 10 gallon hat and smoke a big fat juicy cigar . 
cheers johno

[johno]

OK power 101whp last year.
My goal was +106 to enter Mike's  hp result. But I got a little bit more torque than his published dyno graph

But, dyno results differ from one day to another and probably more between different dyno's, weight of rear wheel and tire pressure.

I hope for more next time. Another head with Kibblewhite 33.5/28.5 mm valves. The smaller valves hopefully not a restrictor. The port job might compensate for it.

101hp head with 34/28mm valves, K2 head. (Stock F2 in valves, Kibblewhite stock size.) Chambers fixed by myself to be more even, no shape to fit pistons better.

Hi Per,
just visited your previous posting re engine output difference between your engine and Mikes engine, if same cam and the heads flowed the same then a 3 deg cam adv or retard difference would equate to the HP torque difference you stated but looking at your ports I feel that is the difference, maybe giving you an edge in torque but less horsepower than Mikes. I also feel given the number of kilometres you do the head you have would be a good choice as it has good support around the guide, sacrifice some ponies for longitivity. However if you want to build a dyno competition engine the biggest gain will be from your ports or combo of ports and bigger cam. Not good for Sunday ride with wife though