CB750f2 damage pistons

[jo007]

HI all

I am a newbie here and in desperate need of help.

I have taken the engine off my CB750f2 and the pistons are clearly damaged, what I dont seem to be able to work out is how to take the Cylinder block off in order to replace the pistons.

https://photos.app.goo.gl/qZawh4X78DwDd5ab6


I have, in the last picture, highlighted in yellow the part I am trying to remove although I am opened to suggestions from those more mechanically oriented.

Any help would be greatly appreciated.

Thanks

[Evil Hans]

I can't see any of those photos apart from he second-to-last.
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Triumph Sprint ST 1050. And it's Red.

[Teflon-Mike]

Which CB750?
FII is very different beast to an F2....
Also erorr 404 file not found when I click the links, too.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[stinkwheel]

If you want to share photos from google photos either bung all the ones you want to share in an album, click on that album then click the "share" icom (three blobs linked by two lines) and post the share URL on here.

OR if you want to do individual hyperlinks or embed the images you need to navigate to the album they are in, click on the share icon, copy the share link/URL then open that in a PRIVATE browser window (if you are logged in, only you will be able to see the pictures). Click on the picture you want to share and use the URL for that picture (either ffrom the address bar or right click and copy image address). You can then post that link to the forum or wrap it in IMG tags.

Like this:

[jo007]

Hi guys

Thank you all for highlighting the issues with the pics!

Hopefully all working now.

[stinkwheel]

Are the pistons all moving? I'm not sure what damage you're seeing there? Not immediately obvious on the pictures. Maybe a tad black like it's been running rich or burning some oil.

This is more general advice. Double and triple check for any nuts/bolts you may have missed. They do like to hide the odd one here and there. Look round the back, look down the camchain tunnel. Use a torch and mirtror if necessary.

Then all that can really be holding it is the base gasket sealant or corrosion round the studs.

I sometimes find removing the studs gives you some extra wiggle-room, you ought to be able to unscrew the studs in most engines from this point by locking a couple of nuts together on the top of them. Those two at the front in particular look problematic. Lots of corrosion around them which could be binding the alloy to the steel stud. They want feeding a load of penetrating oil then see if you can get them out or at least moving. Heat cycling and applying penetrating oil can help free them off.

Then it's a case of persistant wiggling and gentle tapping to try to break the seal on the base gasket. Be incredibly cautious. I can see you've already found how easy it is to break cooling fins. I use a rubber mallet. I'd probably try tapping upwards on those chunkier bits of plain metal in the centre of the block (but it's alloy, so be aware you can break that too).

Do not try to pry them up and off with anything. It's tempting to do so but you'll wreck the gasket faces.
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jo007]

Hi Stinkwheel

Very helpful mate, thank you. Yes all pistons moving although they have a lot of marks on the top where the valves have been tapping them and hence my reason for wanting to replace them, I will clearly have to look at the timing etc, again, more than willing to take suggestions as I would love the acquire the necessary knowledge to put it all back together properly !! it was indeed running very oil rich also. You are soooo right btw about how fragile the fins are

The studs do look like they are somehow bonding to the block, as you have rightly pointed out! I can see a lot of corrosion in them when I look through the gaps as they go through the block.

Thanks again for your help!

[Easy-X]

I've had lots of "fun" just trying to get single barrels off... best of luck
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[jo007]

Hi Easy-X

Any tips? as I fear I will be having just as much fun as you!!

Cheers

[steve the grease]

[jimspeed]

Even zoomed in I cant really see any damage that would warrent piston removal really, recent valve contact would leave shiny marks in the cut outs and the valve stems are so tiny they would just bend out the way before doing any serious damage to the pistons.
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,"Alpha-9: Is there any correlation between dyno rod and dyno kits?"

[stinkwheel]

[jo007]

Well gentleman, that's music to my ears!!

I did say I am a newbie and I didn't just mean to the forum.

Thank you so much for your help guys!!