Author Topic: CB750F2 .... silk purse from a sows ear.  (Read 31585 times)

Offline Spitfire

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #90 on: August 15, 2018, 07:53:06 PM »
I had a problem getting my F1 barrel off, one of the steel knock pins (corner one) had rusted and was holding the barrels to the crankcases together, it took quite a bit of gentle persuading to shift it without damaging the fins, maybe you are facing something similar, if you are certain that you have all the bolts out that is.
And Nurse Julie is correct that the original Honda head gaskets were extremely sticky and very hard to shift.


Cheers

Dennis
1976 CB750F

1977 CB750F2 In bits

1964 BSA A65R In bits

Offline Trigger

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #91 on: August 15, 2018, 09:10:35 PM »
hell yes.... Julie mentioned it right at the start, and so far I have seen exactly why. The carb rubbers are like steel....the o-rings are brittle, the pucks had to be peeled off the carriers like old chewing gum off the sole of your shoe...

And that's just the top end.

I will be replacing every bit of rubber I possible can, as none of these items will ever seal, and would most likely crumble to dust. I do need to find a source of replacement rubbery bits though. Seen a few sets of 'engione rubbers' ... but no description of what's included. So will need to make a few phone calls before I unlock the credit card.

I have a large stock of engine Viton 0'rings, pucks, engine seals and so on. Send me a list of what you require and i will put some prices.

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #92 on: August 16, 2018, 09:38:37 AM »
Thanks Trigger 😀

So far, I have o my got halfway down .. but the list is:

8 tappet inspection o rings
6 pucks
4 small ovrings for the oil jets and the other 2 oil holes.
O ring on cam chain tensioner plunger shaft

That's so far ..  the list will grow as I haven't reached the cam chain guides, guide wheels, crank oil seals, gearbox oil seals and suchlike

The cam chain tensioner rubber block is pretty rock hard, but I suspect that would mean replacing the whole shaft. The metal plate has very little wear though.

Dennis ...thanks for the tip. I have doused the areas I can with penetrating oil, and will let it sit for a day or two. I have undone all the bolts shown in the picture, so it is just gasket grip or something corroded in place. Could be time to start making some wooden wedges.....
« Last Edit: August 16, 2018, 09:45:59 AM by SumpMagnet »
CB750F2 - in pieces
CB900F Hornet - the daily transport

Online SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #93 on: August 16, 2018, 09:22:33 PM »
In the red corner........the CB750 lump.
In the blue corner ....... the ameteur mechanic.

After 2 falls and a submission....off with it's head was the cry! Yes....we got it done finally.

As always, these things have good and bad...so lets kick off with the bad.

1) I am not the first guy in here, and there was a little tell tale mark where someone had pried the head off before. Nothing serious...but of note for me.

2) The 4 bolts under the pucks were different. 2 were clearly replacements lacking the cast in washer and being fully threaded rather than a plain shank.



Now...the better stuff.....well...for me anyway!

The bores look really nice. No rust marks, no scoring and no discernable ridge at the top of the bore. I could see the horizontal hone marks but no evidence of vertical scoring or marks that looked anything like wear.



The o-rings around the studs were incredibly shot. One looked like a dead slug, and the others were crunchy. All will obviously want replacing. Going to need to clean out the muck around them too.



With the head on the bench,I did the old seal test.... pour a little fuel into each head..and see if it stays there. 2,3 and 4 were good as gold...but pot number 1 dribbled it's contents out through the exhaust valve. Not a surprise....I was told more than once on here that the exhaust valves were wear prone. The heads were pretty coked up, with quite a bit of carbon on the valves, but underneath things looked pretty good.



The barrels neweded a good clean from the oil I had dripped down there, mixed with some loose carbon...but once cleaned, things look nice. The pistons all look quite carboned up, but it all rubbed off pretty easily. Barrels off next, so I can check the piston skirts for wear. For now...I got some more oil soaking down the studs ready to lift the barrels tomorrow.



CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Trigger

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #94 on: August 16, 2018, 09:30:01 PM »
Thanks Trigger 😀

So far, I have o my got halfway down .. but the list is:

8 tappet inspection o rings
6 pucks
4 small ovrings for the oil jets and the other 2 oil holes.
O ring on cam chain tensioner plunger shaft

That's so far ..  the list will grow as I haven't reached the cam chain guides, guide wheels, crank oil seals, gearbox oil seals and suchlike

The cam chain tensioner rubber block is pretty rock hard, but I suspect that would mean replacing the whole shaft. The metal plate has very little wear though.

Dennis ...thanks for the tip. I have doused the areas I can with penetrating oil, and will let it sit for a day or two. I have undone all the bolts shown in the picture, so it is just gasket grip or something corroded in place. Could be time to start making some wooden wedges.....

No O ring on "O ring on cam chain tensioner plunger shaft". There is a seal in the housing but, DO NOT disturb this as they were not a separate part  ;)

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #95 on: August 16, 2018, 09:51:44 PM »
Hmm...I dread to ask what happens if that leaks oil.... I suppose it's just splash lube there, but the rubber seal is pretty firm. Don't know if it is up to the job of sealing. But I suspect the solution requires handing over cash for a good used item in the hope that it is in better condition....
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Trigger

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #96 on: August 16, 2018, 10:04:39 PM »
Typical looking USA wheel on the cam chain tensioner, chewed  ;)
Wait until you get to the oil pump  ;D 

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #97 on: August 16, 2018, 10:19:03 PM »
I guess the oil strainer is where all the missing bits of ...well...everything... ends up. Bits of crusty camchain tensioner, bitsof o-ring, bits of gasket goo, bits of whatever fell in there. At least I know the pump was still working as the top end was wet with dirty old oil, and the restrictor oil jets were clear. I hope.

At least with the head and barrels off...the motor has got to the point where I can lift it up onto the bench without risking injury.....so I can wrestle with the chewed screws on the side casing and open up the bottom end.

In the meantime, though.,....I found a use for that old seat. Makes a perfect place to park my backside while I was working on the top of the motor.
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Bryanj

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #98 on: August 17, 2018, 03:51:56 PM »
Guessing from the pistons i would guess you need new guides as well as maybe valves

Offline royhall

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #99 on: August 17, 2018, 04:51:18 PM »
Typical looking USA wheel on the cam chain tensioner, chewed  ;)
Wait until you get to the oil pump  ;D
Are they different on the USA models Trig?
Current bikes:
TriBsa CCM 350 Twin
Honda CB350F in Candy Bacchus Olive
Honda CB750F2 in Candy Apple Red
Triumph Trident 660 in Black/White
Triumph T100C
Suzuki GS1000HC
Honda CB450K0 Black Bomber
Honda CB750K5 in Planet Blue Metallic (Current Project)

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #100 on: August 17, 2018, 05:12:23 PM »
Got the barrels off today after a major fight....and hte pistons are really nice skirtwise. No signs of scoring or rubbing. I need to give them a bit of a clean as they are oily from the oil I put down there .... but them and the barrels look good to go back in as they are.

The head....yes. I have at least one exhaust valve not seating properly, and to be honest...I think it would be silly to put it back without replacing the valves and having new guides. I would also want to look into getting the cam plain bearings re-worked if that is possible. Still need to see what the main bearings are like.

Barrelslook fresh as a daisy inside....but getting them off. Not fun. Now...the K series engines have 8 little plugs with seals that fit over the top of hte barrel studs. On the F2, Honda decided to cut that to 4.... and that leaves recesses to collect condensation, muck and whatever. This had gummed up a couple of the studs, making it a job to get the barrels off. The only seal they have is a rubber one at the bottom....to make sure whatever gets in can't get out... A bit of surface corrosion on 2 of the studs, and a collection of crud which needed a good soak with oil before it shifted.

Camchain guide wheels are rock hard....as was the tensioner blade. Where they run on the chain, it has pitted the rock hard rubber. All fit only for the bin...

So...next job is to look for someone I can send the head off to.....not at all confident about refacing valves and seats, and fitting new valve guides.

Then source a full gasket set ( spotted an NE set on E-Bay which looks pretty comprehensive ) and will also pick up the camchaion tensioner parts to put away for the rebuild.

Can anyone recommend me a good engine paint? I want to strip and repaint the barrels and cam cover ( head will get done later... ) I want a nice glossy black finish :)
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Laverda Dave

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #101 on: August 17, 2018, 07:30:08 PM »
I took my 250RSA engine cases to I Cleenz Machinez in Penge, SE London.  The original black paint was a bit rough so I had them aqua blasted and repainted.  So far the finish has stood up well but the engine is apart again after a siezure (read my CB250RS rebuild thread for the full story!).  The painter did an excellent job, everything was properly masked, no overspray anywhere.
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #102 on: August 17, 2018, 08:06:43 PM »
I'll give them a call and see what's what :)

Meantime...i did solve one problem. The bike was leaking oil from, the alternator cover.... Just took it off and found out why. Only half the gasket is there. Plus 2 bolts had been put in that were obviousdly short, and stripped the thread from one of the lower bolts. All the screws are pretty rough...so I suspect I will not be putting them back. Time to buy that helicoil set.....

I also have my first unshiftable screw. Well....I knew it was FUBAR...but I had to try. Will have to drill it out to get the left hand gearbox cover off. I also have no way to undo the 3 screws on the end of the alternator cover as those are well rounded out. At least I can attack those off the engine with the cover off.

Can't complain...as 90% of the screws have undone nicely, and quite a few of them had been butchered before.

Also on the good news front, the pistons all look good. No nasty scoring and just light wear on the skirts.
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline paul G

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #103 on: August 17, 2018, 09:17:42 PM »
Things now moving along at a nice pace. Keep up the good work.
Honda CB400 4
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Re: CB750F2 .... silk purse from a sows ear.
« Reply #104 on: August 20, 2018, 03:46:45 PM »
NgggggGGNGggnnsngngdfkgnfdgngngnnn.....

that was the noise I made when I started cleaning the rest of the odds and sods off the frame. A random set of 'earth' wires seem to have been bolted on, which may have been related to the electrical issues I was told about before I bought. Especially the one by the coils..

The loom is quite corroded on the terminals and the wires seem to have lost a lot of the flex they should have. It's also been unwrapped around the headstock...which is usually an area of concern with a loom. That's where wires tend to break internally leading to all sorts of interesting 'amusements'. I had a Moto Guzzi that did that to me. First the horn would sound on full lock...then the lights would go out when you turned....and finally when I went to swap the head bearings...I found it had been arcing across the ball bearings...which it was using to earth everything up front.

I might go crazy and buy a pattern loom from Dave Silver Spares so I can refit a good set of fresh unbroken wires for the inevitable electrical fault finding. That's one to bear in mind.

I have enough stuff off the motor to make it light enough to get up on thw workmate now...so I can crack on and strip the gearchange side. I also need to get a 3 leg puller.... I did have one, but it seems to have gone AWOL. No idea where...but I must have lent it out, and not got it back. That's the danger with tools you use rarely. I presume it's a 3 leg job to shift the rotor off the end of the crank...

I also need to consider what I am going to do with the alternator end cover. It's a bit scuffed and needs either replacing or refurbishing as it is pretty grotty. Someone has tried to repaint it black with matt paint. Now...the screws holding the fixed magnet on to the case are chewed. One certainly is already pretty rounded off and I doubt it will shift. Not sure how much bolt length is going to be left if I drill it....and I can't use heat

The jobs and parts list is growing....but the whole thing is breaking down into smaller and smaller assemblies, and the amount of 'bike' left is pretty reduced. Soon...I am actually going to have to start spending money and doing stuff other than taking it apart!
CB750F2 - in pieces
CB900F Hornet - the daily transport

 

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