Topic: 1978 CB750A Turbo Build

[LiveeviL81]

Hello,
I am currently working on upgrading the engine and components on my Turbo CB750A Build. I purchased this bike two years ago, spent one year and a thousand miles on it after rebuilding the carbs and changing the oil. I then spent last winter putting a custom draw-through GT-15 Clone turbo and HSR-42 carb on the bike. I then rode the bike for another year and another thousand miles before tearing it apart this winter and realizing every single cylinder had blown the head gasket and started leaking around the base. I plan to update this build with photos of the history of my progress of the bike until now, and continue to update it with my further improvements this winter as I bore it to 836, and get some upgraded con-rods, targeting 100 HP crank (though I am not sure how to measure that with the torque converter).

Thanks!
Kaleb

[LiveeviL81]

Here are some photos from the first summer I had the bike.

[newday777]

"every single cylinder had blown the head gasket and started leaking around the base"

What were you running for boost?

[MauiK3]

Will that transmission handle the power?

[MRieck]

The very small hyvo primary chain with no tensioner system will not last at all. Just NA builds quickly destroy the chain. If you figure out a solution to that please PM me.

[LiveeviL81]

Will that transmission handle the power?

I have yet to tear into the transmission since the last 1000 miles with the turbo, but from what I've read, these should be good to 100ish horsepower. Since it has the torque converter, it's not like it is doing clutch dumps or anything, just torque.

"every single cylinder had blown the head gasket and started leaking around the base"

What were you running for boost?

I started the year with 10lbs, but the last 2-300 miles I was pushing 15lb with some 18lb spikes if I didn't let off the throttle while shifting. Since the shifting is purely oil driven, no-lift shifts are possible, but as the TC slips, it over-boosts like crazy! Stopped doing that pretty quick!

The very small hyvo primary chain with no tensioner system will not last at all. Just NA builds quickly destroy the chain. If you figure out a solution to that please PM me.

That's news to me, I was under the understanding that the hyvo primary chain was beefer/stronger that the manual transmission chains. Though the lack of a tensioner is also something I noticed myself and don't necessarily have a solution for. May talk to Ken (CycleX) and see if he can cyro-treat the hyvo and hope that helps.

[LiveeviL81]

Some more photos of the turbo and carb

Originally a GT-15 Clone with a carbon seal, later downsized to a TD025 with a carbon seal. Both are interchangeable with just a few hose clamps and bolts, So after the rebuild I'll see which I like.

Carb is a Genuine Mikuni HSR42, lots of modified settings for the carb.
Idle Speed Screw:             Out 4.5 turns
Idle Mixture Screw:           Out 1.75 turns
Main Jet:                          Drilled to .070"
Thunder Jet:                     Out 4 turns
Pumper Start/Stop:           1/16 - 3/4 Turn
Pumper Nozzle                  Drilled to .09mm
Pilot Jet:                          10
Needle Location:               4 from top
Needle:                            Leaner from stock, but custom sanded
Filter:                              Pod
Float Height:                    17mm

This still wasn't a perfect setup, fast roll-on throttle would lean spike and cold start was crazy rich even with no choke.
Been thinking about going to a CV Carb since the engine always "Lugs" when going WOT from cruising due to the Torque Converter.

[LiveeviL81]

Some photos of me routing the exhaust for the turbo and then painting with high temp paint and wrapping it.

Some of the photos are pre-external wastegate, some are post. I redid the exhaust paint and wrap when I added it.

Kaleb Tuinstra

[MRieck]

Will that transmission handle the power?

I have yet to tear into the transmission since the last 1000 miles with the turbo, but from what I've read, these should be good to 100ish horsepower. Since it has the torque converter, it's not like it is doing clutch dumps or anything, just torque.

"every single cylinder had blown the head gasket and started leaking around the base"

What were you running for boost?

I started the year with 10lbs, but the last 2-300 miles I was pushing 15lb with some 18lb spikes if I didn't let off the throttle while shifting. Since the shifting is purely oil driven, no-lift shifts are possible, but as the TC slips, it over-boosts like crazy! Stopped doing that pretty quick!

The very small hyvo primary chain with no tensioner system will not last at all. Just NA builds quickly destroy the chain. If you figure out a solution to that please PM me.

That's news to me, I was under the understanding that the hyvo primary chain was beefer/stronger that the manual transmission chains. Though the lack of a tensioner is also something I noticed myself and don't necessarily have a solution for. May talk to Ken (CycleX) and see if he can cyro-treat the hyvo and hope that helps.

[/b]
 I have disassembled several automatic engines used for drag racing. 836cc and 915cc. The transmission is solid with the exception of the square damper springs used on the main shaft (I think they are associated with the main shaft....it's been a while.) These springs are not shown on the parts fiche but in every instance they are broken in one or 2 to 3 places. Keith Byers can back me up on this one.
 The chains themselves were beat with a lot of slop. They are are designed for a 45 RWHP bike. While the hyvo may be stronger then the OEM dual roller chains they are still a weak link especially with no tensioner. Ask Mark McGrew what he did about a tensioner though those CR engines were well under 100 RWHP.
 You can try to adapt a CBX primary chain....that will last but I think you'd have a hard time stuffing it in there.

[Don R]

 I had read that the hyvo chains adjust out their own slop by climbing the teeth on the gear when under load. That may cause a wear issue.
 Someone posted a chart of press punch die springs in the A section. I don't know if they ever found the right ones. 

[Tracksnblades1]

Ball bearing turbo….?

Or just plain bearing journal bearings…?

[LiveeviL81]

I had read that the hyvo chains adjust out their own slop by climbing the teeth on the gear when under load. That may cause a wear issue.
 Someone posted a chart of press punch die springs in the A section. I don't know if they ever found the right ones.

Don, are you talking about the press punch die springs to replace the square springs? I think I remember seeing that post, may go back and look for it.

Yea, I am hoping to not run into issues with the Hyvo chain, but yall got me a bit worried now!

Kaleb

[LiveeviL81]

Ball bearing turbo….?

Or just plain bearing journal bearings…?

Journal Bearings, this originally started as a cheap build to make more power, haven't spent the money or time to research a ball bearing turbo that can be carbon sealed for draw through, and it's not like this thing is my daily, 1000 miles a year isn't crazy for reliability.

[Tracksnblades1]

Ball bearing turbo….?

Or just plain bearing journal bearings…?

Journal Bearings, this originally started as a cheap build to make more power, haven't spent the money or time to research a ball bearing turbo that can be carbon sealed for draw through, and it's not like this thing is my daily, 1000 miles a year isn't crazy for reliability.

Just make sure you use a good engine oil, especially if you’re using gasoline…Some Ball bearings turbo recommend limiting the oil pressure to 40-45psi to prevent seal damage….coking can still be an issue with good oil. Balls don’t tolerate oil coking or contaminants as well as journals.. neither like coking on their balanced shafts’…

Modern diesels have post purge oil and water cooling to combat coking and it still happens with some oils..

[LiveeviL81]

Got some parts from CycleX, super excited. Jugs are currently getting bored to 836 with the Dynoman Pistons.
Been working on trying to clean parts and get stuff prepared for reassembling the case halves. Still need to check the tolerance on a lot of things. Clutch pads, Primary Chain Stretch, make sure the bearing are good etc. Please list anything in the bottom end if I am forgetting.

CycleX did his Racing Crankshaft Refurbish, Main Bearing Oil Modification, installed Dry Film Coated Main Bearings and his Gen 1 Cycle X Con Rods on the Crank,
He also did his engine case main bearing alignment repair and sent some dry film con rod bearings and a Cyro Tsubbiki Cam Chain.

I also got the Kibblewhite heavy duty Studs, a top end gasket kit, and some other covers that match other CB's. Still need to source the specific gaskets to the Hondamatic... Any thoughts?

I also have purchased a mechanical tac and the valve cover/worm gear adapter from ebay. Should be able to add a small Tac somewhere on the bike once I get a tach cable. Right?

My machinist sent me a photo of my jugs after the Media Blasting, he should be finishing up the boring of the jugs today, and I'll be swapping out the head and case halves to get blasted and the head to get surfaced.
I then plan on checking my piston to top of jug clearance and see if I need to get a copper base gasket to keep the compression down. Targeting 8.3:1 - 8.5-1 CR.


Kaleb

[LiveeviL81]

Worked on removing and cleaning the valves today. Had a heck of a time removing the valve guide seals!
Started with cleaning the valves in an ultrasonic cleaner with carb cleaner solution. Worked pretty well, but I foresee a lot of scrubbing with a plastic brush in my future.

Would love to see some ideas for cleaning the domes on the head!

Kaleb

[LiveeviL81]

Finally started assembly on the Turbo CB750A!
I have not been doing a good job of keeping my build log up to date, but then again not much has really happened. I got all my parts back from the machinist who bored my cylinders. I spent a long time cleaning out blasting media from all my oil ports and bolt holes. Going to be changing the oil quick on break in because I am still terrified there is media I missed.
Had to tear apart the torque converter to repair the square damper springs since they were broke.
Finally started assembly, was waiting on some gaskets and time. Started putting together the case half components, but hit a road block with having misplaced the case half alignment pins. Those are on order and should be here by the time I get the transmission/crank all put together and ready to glue the case halves.

Currently working on the kick-starter shaft and I have confused the heck out of myself. Looking at the manual it shows only two poor images of how the kickstart is assembled. I don't think I have the spring/one way clutch mechanism working correctly, because just trying to "Test" it on the bench, it doesn't seem to make sense how kicking the shaft would rotate the engine and not rachet.

Hopefully its something simple, or even correct and you guys could tell me from the pictures. I also re did the roll pin, and now I am not sure why i drove it out, as I have no idea what it does.

[LiveeviL81]

Was able to get the Kickstarter in correctly. That was a pain! No good way to pretension the spring to hook on the Pin, while simultaneously putting the arm of the kickstarter clutch against it as well. Ended up using some small zipties and a vice to preload the spring to where I could just drop it in, then put the shaft in, pop the zipties and pull them out. Looks like the manual wants you to put the other trans components and crank on the top case half where the alignment pins are, then set the bottom onto it. so thats next.

[LiveeviL81]

Been working hard on assembling the CB836 Engine. Ran into a few issues with losing the Tsubiki Cam Chain, and a packaging defect causing me to be one wrist pin clip short. Got the head on and torque to spec, gonna let it sit on the MLS gasket for a day or two while I do the oil pan and what not. Then going to take the head off, and retorque it before doing the top end. Few things so far I have some questions on.

I still am not sure what this bolt is, I think its some engine mount bolt, but it came it a baggie from Ken, and I don't think I sent him it.

I cannot figure out what goes in the threaded hole on the uppercase half by the output shaft near the case-saver.

Some of the nuts for the head arent fully threaded onto the studs even torqued to 22Ftlbs, I assume this'll change some when I go to retorque, but it worries me.

TDC according to my dial indicator is slightly off compared to the ignition advancer marks. And not consistent between 2-3 and 1-4. Should be close enough. I purchased a K cam for the bike and am hoping to get some more low end torque, is there a way to retard/advance the cam without the advancer gear, and how do you know how much you can get away with?

Thanks all,

[LiveeviL81]

More Photos

[willbird]

Been working hard on assembling the CB836 Engine. Ran into a few issues with losing the Tsubiki Cam Chain, and a packaging defect causing me to be one wrist pin clip short. Got the head on and torque to spec, gonna let it sit on the MLS gasket for a day or two while I do the oil pan and what not. Then going to take the head off, and retorque it before doing the top end. Few things so far I have some questions on.

I still am not sure what this bolt is, I think its some engine mount bolt, but it came it a baggie from Ken, and I don't think I sent him it.

I cannot figure out what goes in the threaded hole on the uppercase half by the output shaft near the case-saver.

Some of the nuts for the head arent fully threaded onto the studs even torqued to 22Ftlbs, I assume this'll change some when I go to retorque, but it worries me.

TDC according to my dial indicator is slightly off compared to the ignition advancer marks. And not consistent between 2-3 and 1-4. Should be close enough. I purchased a K cam for the bike and am hoping to get some more low end torque, is there a way to retard/advance the cam without the advancer gear, and how do you know how much you can get away with?

Thanks all,

I read years ago and have taken as gospel that without a dead stop it is difficult to find exact TDC and set a pointer on a degree wheel to that position. I see people using dial indicators a lot without a dead stop on youtube and others often chime and say that it will not work correctly that way. There is enough slack in all of the bearings and pins IMHO to cause an issue, and the dead stop either side of TDC takes that slack out. No really good way to use one with the head on the engine in most cases though.

Bill

[LiveeviL81]

Was able to get the engine fully assembled and painted this last weekend. Left the ARP Bolts and Nuts stay torqued for a week before loosening and retorquing them. I noticed that some of them have a lot less thread engagement than others, All studs were torqued to 15ftlbs and the nuts were torqued to 22ftlbs. Running a Cometic Head gasket and normal base gasket. I am using the original steel washers with the ARP nuts, and notices the APR nuts are taller. I think it'll be okay, but it was a little worrying.

Kaleb

[LiveeviL81]

Here are some pics of the painted engine, went with a "Cast Iron" Color... a speckled dark grey. Was a bit tough getting inside the fins of the head, but I think it'll be okay.

Thoughts?
Kaleb

[BenelliSEI]

Was able to get the engine fully assembled and painted this last weekend. Left the ARP Bolts and Nuts stay torqued for a week before loosening and retorquing them. I noticed that some of them have a lot less thread engagement than others, All studs were torqued to 15ftlbs and the nuts were torqued to 22ftlbs. Running a Cometic Head gasket and normal base gasket. I am using the original steel washers with the ARP nuts, and notices the APR nuts are taller. I think it'll be okay, but it was a little worrying.

Kaleb

Why not take out the washer? It serves not purpose and you’ll have full engagement.

[nvr2old]

Thoughts?
Kaleb
[/quote]  I've always liked that color.  I've used it on several engines I've painted.  Depending on how much you want to do, it would look really nice if you removed one screw at a time from the covers and cleaned the head and re-inserted it, move on to the next one, and so on.  An hour or two of cleaning parts like those and the valve covers and maybe the Honda on the alternator cover would really make it pop.

[BenelliSEI]

My comment got buried in the original post. Those head nuts only 1/2 engaged look dicy to me. Why not eliminate the washer and get full bite?

[LiveeviL81]

Thoughts?
Kaleb

  I've always liked that color.  I've used it on several engines I've painted.  Depending on how much you want to do, it would look really nice if you removed one screw at a time from the covers and cleaned the head and re-inserted it, move on to the next one, and so on.  An hour or two of cleaning parts like those and the valve covers and maybe the Honda on the alternator cover would really make it pop.
[/quote]

I purchased a kit for converting all of the cover bolts with JIS screws to hex head stainless, It looks great! Though it makes me want to do that with the case half bolts as well, or at least polishing their heads. But I worry about untorquing some of the important bolts, even if its one at a time. My big worry is this paint has not seemed to be very good at adhering so far, granted it hasn't been baked yet, but some of the bolts have had their paint flake, and a few small scratches have appeared. I even had some paint removed when using painter tape!

Kaleb

[LiveeviL81]

Was able to get the engine fully assembled and painted this last weekend. Left the ARP Bolts and Nuts stay torqued for a week before loosening and retorquing them. I noticed that some of them have a lot less thread engagement than others, All studs were torqued to 15ftlbs and the nuts were torqued to 22ftlbs. Running a Cometic Head gasket and normal base gasket. I am using the original steel washers with the ARP nuts, and notices the APR nuts are taller. I think it'll be okay, but it was a little worrying.

Kaleb

Why not take out the washer? It serves not purpose and you’ll have full engagement.

I had thought the washers were used so the steel nut wouldn't "bite" into the aluminum casting when torquing the head down, since the stock nuts and the ARP nuts both had the same diameter flange.

[MRieck]

Was able to get the engine fully assembled and painted this last weekend. Left the ARP Bolts and Nuts stay torqued for a week before loosening and retorquing them. I noticed that some of them have a lot less thread engagement than others, All studs were torqued to 15ftlbs and the nuts were torqued to 22ftlbs. Running a Cometic Head gasket and normal base gasket. I am using the original steel washers with the ARP nuts, and notices the APR nuts are taller. I think it'll be okay, but it was a little worrying.

Kaleb

Why not take out the washer? It serves not purpose and you’ll have full engagement.

I had thought the washers were used so the steel nut wouldn't "bite" into the aluminum casting when torquing the head down, since the stock nuts and the ARP nuts both had the same diameter flange.

I'd eliminate the cylinder stud washers too....you want to grab as much thread as possible especially with the puny 8mm head studs. Lube the threads and bottom of the nut with light engine oil

[newday777]

 My big worry is this paint has not seemed to be very good at adhering so far, granted it hasn't been baked yet, but some of the bolts have had their paint flake, and a few small scratches have appeared. I even had some paint removed when using painter tape!

Kaleb

Kaleb
Did you wash the motor, then sand the old paint, then wash again, final step is to wipe down well with denatured alcohol and let dry before painting?

[LiveeviL81]

 My big worry is this paint has not seemed to be very good at adhering so far, granted it hasn't been baked yet, but some of the bolts have had their paint flake, and a few small scratches have appeared. I even had some paint removed when using painter tape!

Kaleb

Kaleb
Did you wash the motor, then sand the old paint, then wash again, final step is to wipe down well with denatured alcohol and let dry before painting?

I had the motor media blasted, cleaned with brakeclean and rags until no more dirt appears, then after assembly before painting I again used brake clean and a rag to wipe down.

[LiveeviL81]

Was able to get the engine fully assembled and painted this last weekend. Left the ARP Bolts and Nuts stay torqued for a week before loosening and retorquing them. I noticed that some of them have a lot less thread engagement than others, All studs were torqued to 15ftlbs and the nuts were torqued to 22ftlbs. Running a Cometic Head gasket and normal base gasket. I am using the original steel washers with the ARP nuts, and notices the APR nuts are taller. I think it'll be okay, but it was a little worrying.

Kaleb

Why not take out the washer? It serves not purpose and you’ll have full engagement.

I had thought the washers were used so the steel nut wouldn't "bite" into the aluminum casting when torquing the head down, since the stock nuts and the ARP nuts both had the same diameter flange.

I'd eliminate the cylinder stud washers too....you want to grab as much thread as possible especially with the puny 8mm head studs. Lube the threads and bottom of the nut with light engine oil

I appreciate your guy's insight. The engine was actually installed in the frame last night... I know the Hondamatic's are able to have the valve cover removed in frame, but I wonder if I can take all of the valvetrain out enough to get to those head nuts in order to remove the washers, or if I'll have to get some buddies to help remove the engine as well... Shoot you guys got me worried.

[BenelliSEI]

Those nuts already have a flat on the btm. face. Take out those washers.

[LiveeviL81]

Ended up taking the top end apart and helicoiling the cam tower threads while it was all apart as well. Scratched the paint a bit getting the valve cover out, but totally possible to do the entire top end in frame. Only real issue was torqueing the cam sprocket bolts with the torque wrench. Took the washers off and covered the threads with oil, tightened to torque spec, then checked again a day later. Got the whole engine back together so now I'll be focusing on getting the exhaust, turbo, and intake mounted up along with the wiring and plumbing for fuel.

I purchased a larger petcock and flange, converting to a Harley 22mm with a 5/16" petcock ID. Found out the stock petcock flange was brazed, so I will also try to TIG braze the fuel tank when I put the Harley bung on it. Any tips for cleaning out light surface rust and draining the tank? I had a ton of issues trying to get all the old gas out where no matter how I shook it, something still sloshed.

I also got ahold of some reverse comstar wheels from a buddy at work, and I was happy to find out they are easy swaps. Bolted right up!

If I push hard, I should have first start this weekend.

[LiveeviL81]

Busy weekend! Didn't make first start, mainly due to the pulled out exhaust stud I wrote about in another thread. Ended up getting a lot of other things done that I was pushing off till "After first start". Fresh rubbers are getting put on the reverse comstar wheels, brazed in the larger petcock bung to use 22mm Harley petcocks with 5/16" I.D. Got the new exhaust stud in, and manifold and preturbo pipe installed.

Thinking about painting my turbine housing for the turbo with some "2000F" paint I have, it has some flash rust on it from sitting, and I think it would look pretty good!

Kaleb

[LiveeviL81]

Is there a good method for priming the oil pump on the CB750A's? Since its a different oil pump system I tried to follow the documentation before assembly, but it made a mess! Was thinking about using a syringe to push oil up in the oil filter area to try to put a "head" on the pump.

[LiveeviL81]

First Start!
Was able to get first start Sunday Night, she popped right off with a little coaxing from the accelerator pump and choke. I am surprised it runs as well as it does with no tuning on the carb yet since the big bore. Plan to install the Lambda Sensor here after a few more minutes of idling and reving to clean out the assembly lube from the cylinders. Everything sounds good to me, a little excess cam chain noise at idle, but I followed a method of HondaMan by releasing the tensioner hold bolt while Cyl 4 Intake Rocker was starting to head down, light pressure in the back to make sure it adjusted, then tightened back up. Will probably need to do it again as the brand new cam chain stretches a bit.

https://www.youtube.com/watch?v=H97wL0DKJIc

Now to the bad part. You can see some oil leak out of the torque converter case cap, tried to RTV it last night and see if I could get a drive in but its still leaking. So I'll wait for the gasket to come in. I also idled it for a few minutes today and saw another leak I'm asssuming from the rubber grommet for the 3 stator wires, So I'll be digging in there as well to RTV.

I also was not able to get the engine to provide torque to the wheel in 1st gear, revving up wouldn't spin the rear wheel anymore than the bike in neutral on the stand. 2nd gear seems to work fine, I did a bit of brake torquing, but didn't want to drive it with the leak on the torque converter cap. Going to double check oil level since the troubleshooting manual says it could be low line pressure in 1. Really hoping no major engine removal issue.

I have attached the a photo of my shifting mechanism, which lets me correctly shift through all the gears, and the kickstand return works as well, but maybe I missed something obvious. More photos to come if the oil level isn't low and I need to open that cover.

Thanks!
Kaleb

[LiveeviL81]

Ended up having to pull the engine from the frame, which sucked seeing all my work go back on the shelves. Engine paint didn't get too badly scratched on the way out though. Took the time with the engine out to try to fabricate my own engine stand/rotisserie. Sadly I didn't realize engine stands are canted back about 5 degrees and doesn't allow the two bore axis to be aligned and rotate the engine. Made mounts to hold the engine upside down for me, but I won't be able to rotate it. Planning to cut some sections out and align the bores in the future for other projects.

Figured out pretty quickly the issue with the engine after splitting the case-halves. The bearing race/oil feed piece for the low clutch rotated in the case and blocked the oil feed to the low clutch. Easy fix, but I am surprised it happened since I can feel the pin and hole align so hopefully that doesn't happen again. Time to clean all the RTV and get ready put the engine back together.

Found another issue. The main oil gallery feed from the filter through the case halves seems to have cracked on the o-ring seal, and while I was seeing 60+psi oil pressure in the main gallery when the engine was running, it worries me enough to try to fix it before putting the case halves back together. Currently discussing in the main SOHC forum about solutions but I think I've settled on attempting to weld it back up with the engine still assembled, and seal it off with some RTV/Hondabond along the steel insert and monitor oil gallery pressure more often in the future.