Topic: Norwegian beginner full engine rebuild

[PeWe]

Do not use a insert for the camshaft. Use a helicoil as they are stronger and use minimal material removal. In an area like a camshaft you want the best strength.  Use some high temp thread locker on the helicoil installation. It will actually be stronger than original.   Want proof:

Say that to 2 CB750 heads I have where helicoils did not last as time-serts do. Many of the helicoils failed at next or a later repair or modification. My K6 head got some time-serts for cam holders 1983.  None of them have failed.
Only helicoil that came loose that the studs got later replaced by time-serts.

An old K1 head with porous alu got time-serts in most M6 threads. Most inserts I have installed got Loctite 272 hi temp and strenght.

 I used Loctite 648 where the alu was porous and where helicoils were replaced by time-serts, threads in alu not wrecked yet.

Time sert and helicoil use same drill size first time.
If first size of M6 time-sert insert come loose due to stripped alu,  big-sert and after that 2 sizes of self threading inserts.
I had to use the bigger self threading in my last ported K2 head where old helicoils were bad.
 There are lot of meat for the cam bolts. The stud side has less.
I had plan to not replace the helicoils, but found they did not work well when tighten the valve cover. Time-serts replaced them all.

I have used cheap helicoil copy recently as a quick fix for one M8 thread for exhaust spigot. I did not want to invest in the time- sert tool set for one or 3 threads.
The cheap version of helicoils at autopart stores have worked better than the real thing I got from my job many years ago.

Personally for my CB750 engines and heads, time- sert inserts work fine, helicoil type not.

Only reason for helicoil type is a quick cheap fix using the cheap helicoil copy set with all tools and 25 inserts for around 30 USD. Time-sert set cost much more.

I have found cheap self threading inserts from China looking exact as the 9mm OD M6 Wurth that cost a lot more.
Drill size 8.2-8.6 mm. I have not tested them yet.
This for threads whith more alu around the walls.

All covers and cam chain tensioner, std Time-sert when needed.

Im sure I'm not alone with these experiences and conclucions.

[rotortiller]

Did you know: A Boeing 747 has 250,000 Heli-Coil inserts as original equipment. There are 250,000 Heli-Coil inserts in every space shuttle. Indy and NASCAR racing teams use Heli-Coil inserts.


I use helicoils all the time, they are great. They are commonly used in the aerospace industry and approved while Timeserts are not.  Helicoils are used for both durability and increased strength. They are found in both engines and airframes from new and recommended/approved for repair. I have never had one fail on motorcycles, snowblower, jetski, helicopter, airplane etc.  Like anything an installation can be buggered up just like the Lords Prayer, when you do not know what you are doing. If helicoils are failing, installation assistance would be my advice or alternately if you are having better luck with the more complex weaker timesert maybe you should stick with it.

The first thing we did with hopped up SOHC 750s as children was to install helicoils to better hold the cam blocks when employing stiff race valve springs and high lift cams. They never let us down while OEM threads would. They are that much stronger! Sometimes a poorly installed (or poor quality helicoil) might back out with a bolt, however that is easily rectified screwing it back in with high temp thread locker at the parent material/helicoil contact surfaces .

What most people do not understand about the helicoil is that is able to expand in to the patent material under torque more evenly distributing the load. This why they will take more stress before failing than the solid insert. This is in addition to the fact that the steel helicoil outer threads are bearing on a larger aluminum surface.   That airliner strapped to your ass is held together with numerous helicoils for these reasons and more.  Helicoils take minimal space, are low cost, generally easy to use, and have superior strength both by design and material.

[VargVegard]

Did you remove the bearing block shown in video below at 3:15?

The lay shaft bearing or whatever its called? yes thats out. but its seems the previous owner has used a lot of brown stuff between the cases, lots of it. can that be a problem?

The 400 has a shaft in the gearbox that needs to come out first. Is the 750 similar?

yes, and yes i removed that.

Maybe you can look into setting up a drill bushing and start drilling that bolt out. Even better let a machine shop handle it.

Have you tried some heat? Blowtorch?

im borrowing a precision drill in two days time, will try and drill it out then. havent tried heat. dont have a blowtorch and scared of ruining things.

[VargVegard]

So i think i ruined my crank case. Was unable to get help, so had to try and drill the last bolt out my self with a hand drill. Long story short i was not able to drill straight, and i drilled to deep. Is this crank case shot or is there hope? Im officially depressed

[VargVegard]

Yep. Thats what i thought.. where can i find a 78 750F crank case? Or will another model fit?

[bryanj]

Which bolt is that, a pic of full half would do. I have, over the years, seen engines run with various bolts missing.

[VargVegard]

Which bolt is that, a pic of full half would do. I have, over the years, seen engines run with various bolts missing.

Its the one pictured below. Problem is that there is now also a small "hole" in the bottom case right beside the bolt. Maybe that can be welded? Could the whole thing be welded and re-drilled etc?

[VargVegard]

That doesnt sound good. I've tried to search around for a cb750f3 cramkcase or engine, but cant find anything. Any ideas? Im desperate here..

[bryanj]

Thats not near a bearing shell but by the output shaft bearing which is quite big.
I think, from memory, the bottom of the hole in lower case has a hole anyway.
Personaly i would get a timesert of the correct thread for the bolt.
If cases are not available must be worth a try. Youre big problem is getting the mating surfaces flat where the weld is! If not perfect you will get oil coming out and possibly down that bolt hole, JB weld would stop the hole leak.

None of the above is a perfect repair BUT  should keep you on the road if done very carefuly and cleanly.

There is also a repair product called Devcon F which is supposed to take a thread but not at a high torque. I have personally used this in a different situation with some sucess

[VargVegard]

Thats not near a bearing shell but by the output shaft bearing which is quite big.
I think, from memory, the bottom of the hole in lower case has a hole anyway.
Personaly i would get a timesert of the correct thread for the bolt.
If cases are not available must be worth a try. Youre big problem is getting the mating surfaces flat where the weld is! If not perfect you will get oil coming out and possibly down that bolt hole, JB weld would stop the hole leak.

None of the above is a perfect repair BUT  should keep you on the road if done very carefuly and cleanly.

There is also a repair product called Devcon F which is supposed to take a thread but not at a high torque. I have personally used this in a different situation with some sucess

Thank you for the help. I will see if i can get someone to help me with this. Really hope i can get this fixed so i can get the bike on the road.

[PeWe]

Cases on eBay. UK seller not far away. Germany has also some sellers of old parts. I think most of it ships from USA in containers.
150-200 euro for a set of empty cases.

Here in Sweden might have
https://www.spinnin-wheel.se/Kontakt.htm

You must mail and ask, good if you know the serial number range. K7 might work too? I think cases are like F2 1978 but silver instead of black.

I asked about K2 cases which they had for around 1800 SEK. I bought a K2 set from a friend.

Another  old set might cost less than repair by a welder and machinist.

[VargVegard]

Thank you! Struggelig a bit to find the various shops that sell parts. The thing i need to find out now is what model cases will fit the interior and top end of the 78 cb750f super sport. Anyone know this for sure?

[bryanj]

Basically 77 and 78 F to be 100% certain of F2 and F3( which may be only a US model)

[VargVegard]

I will search for it until i find one, thank you!

[PeWe]

I will search for it until i find one, thank you!

A friend of mine has. I asked him.
You got his email in a PM so you can check with him, compare serial numbers just for sure.

He helps people in Sweden, mostly engine repairs/restores, often known via http://www.classichonda.se/

[VargVegard]

Thank you very much! Really appreciate it:)