Topic: 750 DOHC Project

[ljonny18]

Just an observation, but the bottom case main bearings show wear, they are worn through to the copper layer. The clutch basket is sometimes lose and would make a noise in neutral with the clutch out, that noise going away with the clutch pulled in. Primary chain often makes noise as well. The window on the shifter should be enlarged as per Honda TSB for a lower chance of missed shifts/possible popping out of gear. The exhaust valves should be checked especially on the inside cylinders. Might make sense to build a bigger motor now on your cases with a 900 crank/and a bigger block (1000 and 1100 blocks had better cooling fins)

those are desirable factory "sport kit" (in US, standard in Europe) rear sets, there should be a corresponding throttle control with the cables coming out on top.....another desirable piece if you have it. 

CB1100f.net is a great resource for you build.

I may have an old beefy ATK aluminum swing arm for that bike. If you want me, I will look for it.

@somesuch - thanks for your input / advice - its much appreciated !!! Yes the bottom case main bearings do show wear !!! The are very smooth just the copper color has worn through - these will be replaced along wit the top case bearings Than ks for the other tips re the knocking noise !! I will keep them all in mind on rebuild and will replace all worn parts (including the cam chain and all valves).
"The window on the shifter should be enlarged as per Honda TSB for a lower chance of missed shifts/possible popping out of gear" - This is the first i have heard about this... I will look into it !!! can you also expand
ha - its funny, as I had also thought about a bigger block etc.... however, this is my first project that I am using mainly as a learning experience more than anything else without breaking the bank too much (e.g. its not the end of the world if it all goes t*ts up) plus I already have the 750 top end parts etc...

Thanks again, Jon.

PS - I already have the project documented on CB1100f.net and have already recieved a lot of valuable advice !!!

[ljonny18]

ljonny18,
     That is a Very Nice mountain bicycle  ; who is the manufacturer ?

@grcamna2 - it is a "Whyte" mountain bike. It is a British company and this bike is hand-made This model is no longer manufactured, however check out there current products they have some great stuff:

http://www.whytebikes.com/

[ljonny18]

WOW! Such a fast developing thread! Great job Jon.

@FrankenFrankenstuff - Thanks to you I started it in the first place Thanks again, Jon (PS - did you get my mail re the side covers ?).

[grcamna2]

ljonny18,
     That is a Very Nice mountain bicycle  ; who is the manufacturer ?

@grcamna2 - it is a "Whyte" mountain bike. It is a British company and this bike is hand-made This model is no longer manufactured, however check out there current products they have some great stuff:

http://www.whytebikes.com/

Jonny,
   How is the overall stiffness of your solid box section Aluminum frame Whyte Mountain bicycle ? are the suspension components multi-adjustable for Compression & Rebound damping ?

[ljonny18]

Jonny,
   How is the overall stiffness of your solid box section Aluminum frame Whyte Mountain bicycle ? are the suspension components multi-adjustable for Compression & Rebound damping ?

@grcamna2 - To be honest, for a 10 year old bike it is a very good ride !!! Although, I must say, it does take some time getting used to in comparison to a standard "fully" setup (especially on more technical trails etc...).

I may be wrong, but I believe that Whyte only made this bike for a couple of years, and during this time the bike was very successful within competition based mountain bike races against other mountain bikes of that era.

The frame feels solid and stable over all surfaces, and the handling is also very good (it can be flicked around really well). I must say that, although I love riding this bike, I (personally) think that the standard front fork based suspension of "today" is better and easier to get on with - Having said that, I feel I can ride my Whyte just as fast as my other (newer) fully with a standard setup. I can keep up with (and even pass) my mates on it anyway And yes, the suspension (both front and back) is adjustable for both compression and rebound !

Hope this helps....

[ljonny18]

@ grcamna2 - This is a review of the first ever PRST model (1) - maybe you find it interesting and it has some further info that you require !? : http://www.dirtragmag.com/reviews/whyte-prst-1

Note: If you keep your eyes peeled, you are sometimes able to get these bikes for v-good prices (especially considering how much they cost new and for what they are / the engineering that has gone into them) prices on Ebay etc... although there are not many of them about, so if you can get your hands on one ut will be a rare thing - this is why I will never sell mine



PS - Sorry to all the none mountain-bikers for the slight diversion in this thread - I will be back onto the CB750 again with this weeks (slow) progress soon !

[grcamna2]

ljonny18,
     I never owned a suspension bicycle..I have a Specialized "Hardrock" of 1990 Vintage which is hard on my 55 year old bones..I need to keep adjusting tire press. to compensate for these sharp bumps on the pavement in PA.
I was curious if you lose forward momentum power as you pedal standing up and sprint on a suspension bicycle? compared to the stiffer non-suspension bicycle ?

I don't want to turn this thread into a "bicycle" discussion so I'll quit...sorry  .

[ljonny18]

@grcamna2 - if I  lose any forward momentum (in comparison to any other full suspension bike) I am not aware of it, theoretically, the way the frame is setup, it does look like it should loose more momentum, so I can see where you are coming from. However, in comparison to my hard-tail (only suspension at the front) and my road / race bike, this bike does loose a lot more forward momentum (you notice the difference greatly when riding up-hill)... but I must also say, this can be said for most fully setup mountain bikes !!!

[grcamna2]

I never owned a Bicycle w/ shock absorbers  & don't know much about Suspension Bicycles and I thank you for that helpful Knowledge  .

[somesuch]

If you look at the shifter shaft (on the clutch side) you will see a metal frame that hits the stop at the end of it's travel (up or down)  ....so grind a bit the inside of that stamped metal window to allow for more travel, I think it was about 1.5mm-2.0mm or so on each side. Pay attention to the detent that holds the drum in the position, and do not enlarge the window so much as to allow the drum to "over rotate".

[ljonny18]

If you look at the shifter shaft (on the clutch side) you will see a metal frame that hits the stop at the end of it's travel (up or down)  ....so grind a bit the inside of that stamped metal window to allow for more travel, I think it was about 1.5mm-2.0mm or so on each side. Pay attention to the detent that holds the drum in the position, and do not enlarge the window so much as to allow the drum to "over rotate".

@somesuch - thanks a lot for the post !!! it has been noted and will be carried out when I get that far !!! Thanks again !!!

[ljonny18]

I think I have found a pretty serious problem (if I have understood everything correctly) :

As I am waiting for parts (the parts I know need replacing ... ) to arrive, I decided to check the Primary Chain (according to the steps id the book (Haynes Manual) :



Sorry, I accidentally cut some of the text off during scanning and was too lazy to re-scan the page The text basically says to "... assemble the chain around the crankshaft and primary shaft sprockets, anchoring the crankshaft against suitable stops ... and apply a tension of 36kg (79 lb) ... with the chain under tension, measure the chain length ... The nominal length is 129.87 - 129.98 mm (5.109 - 5.117 in) ... The chain must be renewed when it reaches the service limit of 131.1mm (5.16 in)" :



I am guessing looking at the pic (fig 1.7) I need to take the measurements form the outside of the 2 shafts I was not sure, so measured from both the outsides of the shafts and inside of the chain (both of which were greater than the recommended renewal length of 1.31.1 mm (5.16 in))

The chain did however look quite long in comparison to these figures what laid out in a rectangle (theoretically at the the shortest distances) - Note: I know this is completely inaccurate and irrelevant in comparison to the figures etc... Am just thinking "out loud" in a thread :





Anyway... onto some more accurate measurments:

I knew my weights would come in useful for something The book said to use 36kg (which seemed a little extreme ) :

It was difficult to be 100% sure that te shafts were completely straight and supports in a stable / safe manner to prevent bending (not even sure if this is possible) or falling etc... but I did my best to get an accurate measurement...

This picture it just to show where I took the measurements from (from what I understood from figure 1.7 above) :



Ok. So the length of the chain under tension, between the 2 points (outsides of the 2 shafts (top of cam shaft and bottom of primary shaft) was well over 130.1 mm - the reading was different each time, bot the average was more like 141.1 mm !!! with the measurements from the insides of the chain being even larger !!!

So a few questions arise (although I think I will play it safe and simply renew the chain)... :

1). Have I measured / tested this correctly

if so...

2). Im assuming the chain is knackered (is in desperate need of renewing)

3). Could this be the cause of the knocking noise when the motor was together and running ?
4). Could this explain why the primary chain tensioner is worn ?
5). What would cause a primary chain to be so worn - should I be worried

Further to this, I seem to be having trouble getting hold of both a primary chain and tensioner / guide from any local dealers as its not is stock and not available to order etc ...

Any suggestions / help again and as always is very much appreciated...

[grcamna2]

Hi ljonny18,
        I looked up the part # for you're primary chain #13610-393-004..50 link chain for the Honda CB750F and I also see that the part is discontinued.It's possible if you take that part# and the part # for the tensioner and do a Google search you may find them.I also have tried certain Honda Dealers who have some Vintage Honda parts..they may have you're parts & if not they sometimes have a locating service to see which Dealer has these parts in stock

[ljonny18]

Hi ljonny18,
        I looked up the part # for you're primary chain #13610-393-004..50 link chain for the Honda CB750F and I also see that the part is discontinued.It's possible if you take that part# and the part # for the tensioner and do a Google search you may find them.I also have tried certain Honda Dealers who have some Vintage Honda parts..they may have you're parts & if not they sometimes have a locating service to see which Dealer has these parts in stock

Thanks grcamna2 - I did just that, I googles for the part number and think I have found a new chain that is also local Thanks for the tip !!! Just need to find a tensioner now

[ljonny18]

OK, I have not posted for a while ... I am at that stage of the project (that I and I guess most people hate) when I am waiting for both funds and parts

I have been having problems getting hold of a Primary Chain tensioner and guide as they have been discontinued and most dealers don not have any in stock. I did however manager to get ones in v-good condition (especially in comparison to my current parts) from a member on a CB forum:






In the meantime I have managed to sort another level of cleaning out on my engin casings using dry ice :

Before:














After:











They came out pretty good, I pb dont even need to get the motor painted anymore !!! There were 2 layers of old crusty paint (first black and then silver) until it got down to the original metal - It is now (almost) like new and I can now even see / read the original engine bearing codes (engraved into the casing) - I wish I had been able to read them before I spent a whole weekend trying to measure my bearings

[grcamna2]

Excellent Job on your parts cleaning; dry ice you say ? !

[ljonny18]

Excellent Job on your parts cleaning; dry ice you say ? !

Yeah, im really happy with the result !!! Thanks - Just need to get the top end done next

Yes "Dry Ice Blasting" - I did / do not know that much about it really... local company that does it was recommended to me by a local engine builder. Apparently it is a similar process to sand blasting, but a lot cheaper and a lot less agressive / safer to use on soft metal  etc...

Here is where I got it done, it is a guy on his own and seems to be passionate about it which is always nice !!! This is his website:

http://www.frozenclean.de/

http://www.frozenclean.de/frozenclean/index.php

Its all in German, but I have (google) translated the basics :

Dry Ice: Dry ice is carbon dioxide (CO2) in solid form. It is nontoxic, odorless and not flammable. The big advantage of dry ice is that after blasting it sublimes completely without having to completely liquefy the residu.

Production of dry ice: Liquid carbon dioxide is fed from a tank into a special machine, called the pelletizer and relaxed. This results in dry ice snow. This medium, with a temperature of -79 ° C is then pressed by a matrix - the result: dry ice pellets in the size of a grain of rice (about 3mm).
 
Dry ice blasting away Oils, grease, wax-like substances, anti-rust paints, sprays, adhesives, resins, organic substances, graphite, carbon deposits, PU foam, film, concrete milk, grime, brake dust, rust, etc..

[grcamna2]

I would like to find a place that does it here in the U.S.,and then hope I can afford it    .

[ljonny18]

I would like to find a place that does it here in the U.S.,and then hope I can afford it    .

The price was not too bad... I payed 40 Euro (about 50 USD) for the complete bottom end. I guess the top end will be a similar price (maybe even less) !!!

[grcamna2]

I'm moving with in a reasonable distance to Atlanta,GA. I hope to find a similar place that will do a few parts for me  .

[somesuch]

Nice!, never knew about such process.

[ljonny18]

I have read that is is a good idea (good practice) to replace the connecting rod nut and bolts when doing an engine rebuild:



Is this really necessary Is it not enough to simply add some loctite red and be done with it ?!? Can anyone shed some light on this ? as if it is reccomeneded I should get some connecting rod bolts orders



Cheers,
Jon.

[somesuch]

It depends on many variables like RPM that the engine will see, the type of bolts, piston weight, etc., but to make the long story short, I have reused bolts/nuts on a stock 82 800F motor that lasted at least 30K after I rebuilt it (maybe more, but I lost track of the bike) .... that said the 750 is a higher revving motor.

[ljonny18]

It depends on many variables like RPM that the engine will see, the type of bolts, piston weight, etc., but to make the long story short, I have reused bolts/nuts on a stock 82 800F motor that lasted at least 30K after I rebuilt it (maybe more, but I lost track of the bike) .... that said the 750 is a higher revving motor.

@somesuch - I checked the book and spec and taken into account with the milage of the motor and previos state, it basically headed towards replacing them, on closer. After further investigation I have decided to played it safe and ordered some new nuts and bolts. Thanks again !!!

[ljonny18]

This will be the back of my seat unit. The original was (unfortunately) hacked off by the previos owner although I think this will look good:



So parts are slowly but surely starting to arrive:

Primary chain and tensioners:





These must be the most expensive nuts and bolts i've ever bought (connecting rod nut and bold set):