Topic: Operation Streetfighter: Motor Build

[HondaMan]

Just for reference:

Honda bigbore ebay

Those come out to $135 plus duty... that's a far cry from $500

@HondaMan: How do those stack up as far as compression/ performance? Is it worth the extra $350 to get the Wisecos?

Anyone who's used em feel free to chime in too!

The 'cheap' ones come in at 9.04:1 or so on the F2/3 heads, 9.2:1 on the others. But, you can also mill the F2/3 heads 1.00mm with them, so it comes back up to about 9.2:1 again. Use the normal piston clearance with these, in the .0010"-.0012" range.

With the Wiseco forged version, use .0022" to .0024" clearance. These make about 10:1 CR with the early heads, and about 9.8:1 with the stock F2 heads.

With either, use the HD cylinder studs, too. Add a quench band to the head, to prevent irregular spark knock issues.

[laminaytrap]

Alright, so this thread has been dormant for a bit as I haven't had access to the pertinent part (Motor)

Now I do and I'm making plans again...

The engine is partly apart

http://s307.beta.photobucket.com/user/lamainytrap/library/Engine%20Pic









Why are the gasket rings all oblong like that?

The rest of the picks are in the first link.

So Budget didn't improve since my last post, and I'm now leaning towards a 2-stage build


                                Now       Later   
Race Cutting            350          Done   
Bore Hone               Later        200   
Head Refresh           Later       300   
Cam                         Later        200   
Valve Springs           Later       70   
V Seals                    Later        20   
Prim Tension            80            Done   
Cam Tension            75           Done   
Shifting Spares        100          Done   
Gasket/Seals           150          50   
Cam Sprocket          Later        40   
Valve Guides            Later        70   
Super Studs             75            Done   
Pistons                     Later        500   
Cam Chain               40            Done   
Clutch Stuff              Later        100   
Total Now              870           1550   Total 2420

[laminaytrap]

Seriously though, any opinions on the oblong gasket thing? Is that an indication of something or a cause of anything?

[Kickstart]

Seriously though, any opinions on the oblong gasket thing? Is that an indication of something or a cause of anything?

That's normal... my stock OEM head gaskets look the same.

I believe I read in HondaMan's book, or in an email he sent me, that it was an easy/cheap way for Honda to get some valve de-shrouding.

Are you going to start a build thread... looks like a cool project.  Good Luck!

[HondaMan]

Seriously though, any opinions on the oblong gasket thing? Is that an indication of something or a cause of anything?

Boy, that's some worn bores & rings you got there! They don't often leak so much that they wash off the piston tops like that. I'll bet that one smoked like my mother did in the 1970s!

[laminaytrap]

@kickstart build thread is in sig.

@Hondaman/others

The bores measured about 4-8 thou out of round, don't know where that lies in the good-bad-ugly scale.

The exhaust valves were pretty seriously carboned up, but i cleaned/lapped them and they came out looking decent till I can afford the headwork. Probably got back 30psi there alone.

So should i slap it back together and see how she goes? Or is it too far gone to get me another month or two of riding. Mid summer budget will be a lot easier on me.

[HondaMan]

@kickstart build thread is in sig.

@Hondaman/others

The bores measured about 4-8 thou out of round, don't know where that lies in the good-bad-ugly scale.

The exhaust valves were pretty seriously carboned up, but i cleaned/lapped them and they came out looking decent till I can afford the headwork. Probably got back 30psi there alone.

So should i slap it back together and see how she goes? Or is it too far gone to get me another month or two of riding. Mid summer budget will be a lot easier on me.

That's a LOT of clearance! Yikes.

When the clearance is more than .0020", these engines start drinking oil. Usually, they go out-of-round about .0004" to .0008" in about 10k miles, and loose significant compression and power. Boring them round again at that time restores as much as 10% lost power ABOVE the original engine power, and the now-cured cylinder liners stay round for almost-ever after that. Clearance on a rebore should be .0008" to .0012" max.

[laminaytrap]

So I guess my butt dyno wasn't wrong then with the state of things in there.

Now I've heard about this magic staying round thing before, but it was also mentioned that by going 836cc this stabilization is negated and I will have to bore again around 10-20k mi in the future, is this true?

[74750k4]

Whatever you do, DON'T use a riveted cam chain. Very few riveted ones I have seen on cammed 750 engines survive very long. There are HD chains available, but one of the best is Honda's "F" series chains, from the 1977/78 F2/F3 bikes. Their middle part number is "-410-".

If you bore to 836cc and use high-compression pistons like Wiseco (use .0022" clearance with those), polish the valves, install a cam like the Megacycle 125-00, install bronze valve guides (you will need those, anyway, at 24k miles on a K7), get the jetting right and increase the spark duration, you'll find the bike completely changed next time you ride it out. Don't use a Dyna S ignition: that will SHORTEN the spark duration, instead.

You will also need HD cylinder studs, a new cam chain tensioner kit for the post-1976 engines, a new C5 gear in the tranny and possibly a new L shift fork. Check the shifter drum to see if the tip of the L fork's groove is worn off, causing the loss of 2nd gear engagement, very common on K7/8 bikes. This then causes the rounding of the gear dogs on C5, often damaging C2's slots in the process. You can send the whole gearbox to CycleX or API for back-cutting, which would be highly recommended if you are also increasing HP.

 

So is this Tsubaki/camellia one from APE, a good one? or, no???

  I used a Tsubaki link to rivet connect it back together without bottom end tear down...

HEAVY-DUTY CAM CHAINS -

Extra heavy duty cam chains are recommended to help eliminate chain breakage which can result in extensive engine damage. Tsubaki is the only true high performance cam chain available. The Tsubaki engineers have worked with top race mechanics world wide to produce the only cam chains that will stand up to the rigorous demands of high performance race machines. These same chains are equally at home in the stock street bike, affording the owner the added protection of a high performance chain at a price less than stock factory replacement chains.

#BFO5Mx94 - CB750 all models thru '78 - $30.22

Otherwise, I think I'm on track with superflow valves, Kibblewhite springs, Dynoman guides, 392 78K head, Kenny Harmon D grind (DP117KHD), which appears similar to the 125-00,  stock bore, Ken Augustine head work, including "mild" porting, HD case/cyl studs. A bit concerned about getting a good pre-oiling pressure before start-up. Just changing the oil with a new filter takes about 15-20 secs of dry (no pressure) spinning.

[Retro Rocket]

So is this Tsubaki/camellia one from APE, a good one? or, no???

Best one to use....

[HondaMan]

Otherwise, I think I'm on track with superflow valves, Kibblewhite springs, Dynoman guides, 392 78K head, Kenny Harmon D grind (DP117KHD), which appears similar to the 125-00,  stock bore, Ken Augustine head work, including "mild" porting, HD case/cyl studs. A bit concerned about getting a good pre-oiling pressure before start-up. Just changing the oil with a new filter takes about 15-20 secs of dry (no pressure) spinning.

That does seem a little long if the engine is already 'wetted'. There's a few things to check for this:
1. The O-rings (2.5x15 size) on the little dowels that align the oil pump into the crankcase. Make sure they are new, and springy, so they seal well.
2. The aluminum seal washers on the inside of the oil hoses were they screw onto the tank. If you haven't disturbed the hoses by unscrewing them, they are fine, but if disturbed they often need to be replaced to seal well.
3. The 2.5x15mm O-rings on the 2 oil hose castings that bolt to the engine. Heat has usually hardened these and they should be replaced often.
4. Inside the oil pump: the #1 leak site is the seal on the shaft between the 2 impellers. You can still get this seal from Honda (look at the GL1000 Gold Wing oil pump, same seal), even though it is not listed for the 750 anymore. It also fits some outboard engines, fortunately, so will be around a while. There are 2 O-rings 2x46mm inside the oil pump covers, too, but they seldom leak.

I have seen this sort of difference after replacing all the seals at once: an engine that took 5-7 seconds of idle speed (1000 RPM) to turn off the oil light changed to about 1 second off on the light, after a full oil change with filter. Pretty dramatic change!

[laminaytrap]

That's interesting, I've never had pressure issues, although I know one of my oil lines leaks at the block oring. Even after an oil change it's usually really quick coming back.

As for people that have issues this is what I usually do for first start anyways:

-Run engine till warm/ park after ride
-Turn off fuel
-Wait 15-20 min for cooling and draining down, mostly so you get it all and don't melt your catch pan
-Change oil
-With kill switch off kick over a few times
-then run starter till light goes off/pressure comes up
-Turn fuel on start as normal.
-Hope you didn't build up enough fuel to blow your airbox off
-Now you're done, and your pistons didn't hit a power stroke with zero oil pressure! That's my main concern.

[2ceebees]

What the heck kind of airbox is that?  I read your build thread but didn't see any info on it.

[laminaytrap]

muhahaha

It's custom, I feel like i took the photos but never did the writeup...

It's basically a plastic tub mated to the ZX6r mikuni's original airbox flange then i put two ports on the back and filters on there. It was crude at best, but also better than nothing.

Due to the angle of the carbs i'm no longer running them, therefore airbox is in the trash. Those carbs are sweet, but not suitable for engines with near horizontal intake ports.

[laminaytrap]

Motor is assembled and running.

Went with early pistons due to availability, bore/hone/lapped valves, reassembled as usual. I replaced the cam chain tensioner, all cylinder and head gaskets and o rings, super studs.

Reassembled now and trying to get my hands on jets.

Currently running pods and hindle glass pack. Looking for #42 or #44 pilot jets and some larger mains. Stock mains are 105, looking for 115 and 120 jets likely, though I can't be sure.
I'm pretty sure on this but I wanted to check that there's no way to change needle position besides completely disassembling the carbs for each swap?

Bike idles pretty rough even with the air screws at one turn out. Runs OK at WOT with the choke on about a quarter.

Suggestions are welcome, hopefully I'll get my hands on some jets by weekend, until then I'm probably going to restrict the filters so its rideable in the midrange.