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<  Performance issues  ~  Forum noob building a 900cc motor.

Deer Slayer
Posted: Thu Nov 01, 2007 12:56 am Reply with quote
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Joined: 30 Oct 2007 Posts: 15 Location: Howell Michigan
Hey guys, I hope to pick some brains for some input here. I've got a bunch of spare parts for honda cb750k SOHCs, and figured I'd do something with them.

I have the following high performance parts I intend to use:
1. MTC ENG Alcoa aluminum connecting rods
2. Dyna 3 solid state ignition
3. Dyna coils with Accel 8.8mm wires
4. Lockhart oil cooler, and adapter
5. Unknown solid state 3 phase voltage regulator/rectifier
6. Henry Abe 900cc big bore kit with stepped sleeves, and unknown compression Rolling Eyes

I could use some help figuring out what compression the pistons are, I think they're Henry Abe the type A, and they say Hainst 900cc inside. I'll have them in my hands in a couple days.

My goal is to make as much power as I can without killing my bottom end torque. I was wondering if I should go with a set of 34mm Mikunis from a kawasaki, or a set of 29mm smooth bores??? I'm looking for the best option without killing my budget. I intend to use some sort of ported head, where do I get the head porting/reconditioning done??? I was thinking the megacycle 125-65 cam would work good for what I want. I have a milling machine, and a lathe, so I can mill the valve pockets if needed. I also plan on lightening my own alternator, so if I could get some detailed pics of both stock, and lightened versions so I can get a better idea where to cut, that would be appreciated. I know there's a lot more to a build, and I'll get to it in another post. Thanks for any advice, I've built a few car engines, but not many for bikes.
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Deer Slayer
Posted: Thu Nov 01, 2007 7:51 pm Reply with quote
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Joined: 30 Oct 2007 Posts: 15 Location: Howell Michigan
Ok, I guess that aluminum rods would expand more than steel when they get hot. Now, the question is HOW MUCH??? How can I use this to get an ammount for valve clearance??? Or, should I stick the aluminum rods on ebay, and get some sort of aftermarket steel rod?? If so, what steel rods are the best bang for the buck???

My second issue is the electronic voltage regulator. It's got 3 yellow, 1 brown, 1 green, and 1 red wire. My guess is the yellows are the output from the stator, brown is the field, red is positive out, and green is ground. can anybody confirm??? The regulator looks like the Accel units, but I was unable to find a 3 phase version on their website.

In my research, I'm still unable to find a number for the compression ratio of the Henry Abe pistons. The kit I'm getting is new in the box, and has the original sleeves. Are they like the Wiseco, 10.5:1, or are they more like 9.5:1???

For carbs I want something that will be somewhat of a bolt on. I've got some $$$ saved for this project, so I don't mind spending for something good, as long as it works.

This motor is going to be on a street bike. I want to keep as much bottom end torque as possible. Confused [/img]
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Satanic Mechanic
Posted: Sat Nov 03, 2007 11:24 am Reply with quote
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Joined: 04 Sep 2005 Posts: 309 Location: Munich, Germany
Hi Deer Slayer,

and welcome to the forum! Nice project that you are laying out here.

Now, a couple of thoughts:

Aluminum rods: I would just not use them, for me they are too unreliable. either put them on Ebay, or polish them up and put them on display in your workshop Smile

Rods are a difficult subject. You may find some RC engineering steel rods. RC used both stock rods and shot peened them, but they also had their own rods (which are marked 'RC'). The best rods available are undoubtedly the Carillos, but they are high bucks. Now, since you are going to build a street engine with good bottom end, and not a high RPM race monster, I would simply stay with the stock rods. I have used a similar setup with stock rods and had no problems at all.

The Dyna/Accel setup sounds good, as well as the oil cooler.

The Henry Abe pistons should have a cr of 9.5 - 10, they have slightly less compression height than the Wisecos. The valve pockets will need some reworking if you use a hotter cam, though, but you are well equipped for doing that.

The 34mm carbs are too big for that displacement. Especially if you want to retain good bottom end, I would either keep the stock carbs or go for 29mm smoothbores or CRs.

Cams. The 125-65 is a good choice, as is Web Cam's 41a. Both provide more top end, and with 900cc (and wer, yet still retain good low end torque, you may also consider Megacycle's 125-25 or Web Cam's 63a. Both still provide good low end, yet you get a good boost above, say, 7k RPM.

For porting the head, Mike Rieck (jmrieck1@comcast.net) has a good reputation in the US and is an experienced CB750 engine builder.

I'll try to get some answers on your other questions soon... I would second your guess on the regulator, but I cannot confirm it for sure.

Later...
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Deer Slayer
Posted: Sun Nov 04, 2007 4:13 am Reply with quote
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Joined: 30 Oct 2007 Posts: 15 Location: Howell Michigan
This guy on E-bay decided to pull the kit after the bid didn't go high enough for him. I spoke with him on the phone in an attempt to identify the kit, so I had his phone #. So, I called him to find out what he wanted for the kit, and he said $650!!!!! Shocked SCREW THAT, I'll try to re-use my old 900cc kit before I pay that, but with less than 10:1 compression, I dunno about going so cam happy. I have 8 pistons (2 kits) all henry abe 900cc, all with valve dents! They came from dead motors taken apart. The one set of pistons has minor dents in it, and it looks like I can mill them out for the additional valve clearance needed to run a high lift cam. The other set of pistons has DEEP dents from the valves, so I don't think I want to try them. The jugs with the sleeves are very rusty, and I'll have to get some new sleeves to make them work. I'd also need new rings, I'm thinking a Wiseco kit is sounding better and better. So, my new build is an 836cc Rolling Eyes . I have enough stuff that I can possibly build a 900cc that's mildly modded when my stock motor gets tired.

As for rods, I'm thinking e-bay the aluminums, somebody will buy them. They may in fact be the cause of the dents in the 900cc pistons. What does a set of carillo rods cost??? Are there any other cheaper options for steel rods that aren't shot peened stockers? Our local machine shop does shot peening, so that might be an option. Also, do they make better rod bolts for the stockers??? I would like to ditch the stock rods, I like to beat on my bike! I've seen the destruction unleashed by a stock rod breaking in a 750, IT'S UGLY!

I dunno how else you could wire the regulator, I'm pretty sure the green wire is gound from my testing with a multimeter. I'm also pretty sure the red is the output. Yellows are definetly the stator wires. That leaves the brown wire, and that is the only wire that doesn't test as if it's connected to a diode array with the meter.

For the carbs, I've seen a few sets of 29mm smooth bores on ebay, which were pretty cheap! Do they still make parts to rebuild them??? Those will probably be my carbs fo this beast. Very Happy
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Satanic Mechanic
Posted: Tue Nov 06, 2007 7:33 pm Reply with quote
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Joined: 04 Sep 2005 Posts: 309 Location: Munich, Germany
$650 for a Henry Abe kit? Oh boy, some people are really insane. If you are unhappy with the c/r, you can always mill the head a bit. If you need new sleeves, the Kawa Z900 sleeves (which were often replaced for 1000+ cc) should work with some machining, but yes, a 836cc (or 850cc from CycleX) is much less work and the penalty is just 50cc or even 36cc.

Last time I asked for Carrillos they were just under $1000, but rumor has it the went up again and are around $1200 or even more. Falicons used to be just a tad bit cheaper (and almost as good), if they haven't gone up too they might be an alternative. Yes, they are both major setbacks, but I absolutely agree, one broken rod does much more damage... It micht be worth asking Carrillo about using their bolts in stock rods, too.

Mikuni still makes RS Smoothbores, although only 34 and up. Several parts for the old carbs are still available.

Oops, my laptop battery is getting weak - more later Shocked
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Deer Slayer
Posted: Wed Nov 07, 2007 8:47 am Reply with quote
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Joined: 30 Oct 2007 Posts: 15 Location: Howell Michigan
Holy cow, that's a LOT of $$$ for some rods! You can get some good rods for a V8 for about 1/2 that! What do you think the aluminum rods would go for??? If they can off set this ammount, I may still be able to upgrade the rods.

I think I'm getting the wiseco kit, it should be good. If I go with stock rods, I'll probably go with a slightly less radical cam. That will keep me from going too rev happy.

I'm thinking some smoothbores are gonna be my carbs, but what about the TMR32 flat slides?? What does a new set of those cost, and how much bottom end torque will I lose?? The smoothbores would probably be a better option if I wind up with the stock rods, and milder cam. But if I go wild with aftermarket rods, and the big cam, would the 32s be a better match???
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mkramer1121
Posted: Wed Nov 07, 2007 11:51 pm Reply with quote
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Joined: 11 Aug 2007 Posts: 11
The aluminum rods will go for between $150 and $200. There are a number of people on ebay selling them in that price range. I just sold a set of those rods for that amount.
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Satanic Mechanic
Posted: Sun Nov 11, 2007 9:42 pm Reply with quote
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Joined: 04 Sep 2005 Posts: 309 Location: Munich, Germany
The flat slides are certainly an upgrade to the CRs and Smoothbores, but they also come with a privce mark - they run about twice as much as a set of CRs. Ouch...

As for choosing a cam, an 836 with an Web cam 41a or Megacycle 125-65 will not loose any bottom end to a stocker, at least not with stock carbs. 836cc, stock carbs, 125-25 or 63a will have almost the same bottom torque than a stocker, but after 7k it will just go wild.

As for redline and revs, Honda itself bumped up the redline from 8500 to 9500 using the same valves and springs when they introduced the '78 K7 and K8. I had the same stock springs in a 900cc engine with 125-25, and it happily went to 9500 no problem.

I just threw a set of Yoshi springs out of a 836, 125-65, 31mm CR engine and replaced them with stock '78 F2 springs and titanium retainers. I will put in a 125-25 in spring next year and put it on the dyno then.
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Deer Slayer
Posted: Wed Nov 14, 2007 3:17 am Reply with quote
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Joined: 30 Oct 2007 Posts: 15 Location: Howell Michigan
I was reading the clymer manual, and it had something about boring the stock carbs to 30mm, that sounds easy enough to do! I've seen carb reamers sold for boring out carbs. I would assume you'd just ream out the carb from the front to the back. The spare set of carbs I have are screwed up because somebody tried to bore them out, and made them all different sizes! It looks like they reamed them in two different spots, trying to open them up more. I know the guy that sold me my bike told me those carbs didn't work right no matter what he did. I think I can pick up a spare set of stock carbs real cheap, and try boring them out. How does boring a carb affect the jetting??? If I bored the stock carbs, and used the stock rods, that would make for a CHEAP build! If the stock rods are happy to 9000 RPMs, and the 125-65 cam doesn't kill bottom end torque, I should be really happy with this build! I'm definetly gonna have the head ported, and do some springs and retainers. Very Happy
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Deer Slayer
Posted: Tue Nov 20, 2007 8:09 am Reply with quote
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Joined: 30 Oct 2007 Posts: 15 Location: Howell Michigan
This is what I was able to find out so far. You bore the carbs from front to back along the path of airflow. You want to offset the bore toward the top of the carb to make sure that the needle is in the same relative position to the outlet of the main jet passage. Also the air opening for the idle will be close to the same, the only thing that changes is airflow! You can also creat an oval shaped bore if you want to go even bigger. You SHOULD NOT go over the diameter of the slide for the bore diameter (this allows too much slide slop). Boring the carbs will result in leaner mixture, you'll have to jet richer. For additional throtle response, you can cut the slide on the side of air intake slightly for high altitude, or HUGE cams. So, anything else that can be contributed might be helpful, so PLEASE give me INPUT!!!
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