Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Alimacdee2 on December 11, 2024, 04:33:59 PM
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fit like,
regards to my 1970 CB750 cylinder head which I'm planning to skim. after a full rebuild with everything replaced I skimped on the head gasket, after just 200 really good miles & showing good compression, I noticed the head was leaking, realised I'd fitted the wrong head gasket, DS did assure I had the correct head gasket set, should have known better! rapid learning curve on gaskets and o-rings. I notice 4 round indentations between 2-3 and 3-4 cylinder, the main oil leak is from fitting the wrong cheap head gasket, noticed 2 of these indentations have allowed a little oil into the head,. Anyone know what these indentations on the head surface are? anyone recognise what these might be?
thanks
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No one has replied to your post, I know less than nothing about the CB750.
I see the small circular marks you are refering to, there appears to be no corresponding areas on the cyliner block to explain them, could the marks have been made by a tool used to either hold the cylinder head when the valves were fitted or even by a valve spring compressor by a PO?
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Indentations are very odd, and shouldn't be there.
Speculation, as Ted has mentioned, looks like it's been clamped or similar for some reason.
Hopefully a skim can be used to fully correct the surface for rebuild.
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Looking at second pic, it's also evident that weird nicks and picks indent etc are present, appear random too. Something odd/variable has happened to the surface that can't immediately be attributed to anything common to that motor.
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Studied the pics but was unable to determine what could have caused these marks! Strangely the deepest marks are all to the same side. Cant think that that side of the head had been impacted with something, but looks as if it’s been clamped, perhaps G clamp type home made valve compressor? Good candidate for skimming for sure.
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I thought the nicks & picks indent was old gasket material distorted by the camera.
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Alimacdee2, I have a spare head gasket you can have. Got it in a full gasket set, with round cylinder cut outs. I have a 1979 F2 which has "egg" shaped cylinder cut outs so had to use a different gasket. You are welcome to the gasket which is unused.
Assume you are in Aberdeenshire.
Archmill (Motherwell)
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I can see what you mean Ted, also I can see others that don't conform to that pattern, when viewing under raised magnification.
There's other effect too, near some of the stud holes are "strakes" appearing to curve, albeit slightly, down in towards those holes. Almost looks like a legacy of hand clearing of gasket previously as possibility.
Quite a few elements that should competently clean up in resurfacing.
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Thanks for those reply’s to my post, and the offer of the gasket, always much appreciated on here, I’ll definitely be having it skimmed , that should remove those marks I hope, maybe that’s all it needs. I’ll let post the result of this. I’ll remove the valves because they want to clean any swarf out of the head.
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The firm I used to skim my 500 cylinder head had a fancy newish machine that could take off really small amounts.IIRC it ended up being just under 5 thou of an inch to remove all the marks near the main sealing rings. The surface was like a mirror, it wasn't daft money either about £40.
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The firm I used to skim my 500 cylinder head had a fancy newish machine that could take off really small amounts.IIRC it ended up being just under 5 thou of an inch to remove all the marks near the main sealing rings. The surface was like a mirror, it wasn't daft money either about £40.
Who did you use Ted?
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I would agree Clamp marks and a lot of them, someone really didn’t want it to move did they! It’s another good candidate for the POs hall of horrors. We really should start one.
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The firm I used to skim my 500 cylinder head had a fancy newish machine that could take off really small amounts.IIRC it ended up being just under 5 thou of an inch to remove all the marks near the main sealing rings. The surface was like a mirror, it wasn't daft money either about £40.
Getting the head set and clamped such that the surface is planar to the cutting blades is important. Shows good method from them in that aspect. Any significant difference from original face would need a deeper cut to correct clamping and machine alignment error.
Ordinarily, first cut is as thin as possible, to then judge how low the low dips are in a competently assessing them. Then to consider just how much needs to come off in cleaning up the errors seen on this example in those dips.
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The firm I used to skim my 500 cylinder head had a fancy newish machine that could take off really small amounts.IIRC it ended up being just under 5 thou of an inch to remove all the marks near the main sealing rings. The surface was like a mirror, it wasn't daft money either about £40.
Who did you use Ted?
Service Garage Ltd, they did all the specialist machining jobs for Mercedes Derby. I know my way there, it's sort of between villages probably Draycott.
Update they are on the outskirts of Borrowash
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Logged!
I've used SEP at Kegworth years ago. Had bearing surfaces on a crank metal sprayed and ground down. Think that was the Superdream 400 too!
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Alimacdee2, got my cylinders and head skimmed at UK Recon, 3 Salkeld St, Glasgow G5 8HE, tel: 0141 429 7338. They did a good job and wasn't very expensive.
If you want the gasket, PM me with your address mate.
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Hi archmill PM sent and messaged Friday so not sure if these are going through.
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Finally got the bike back together, head skimmed up nice, used a Honda base gasket this time, ujsed a Vesrah Head gasket with matching o-rings off ebay from nurse Julie I believe, and thanks for the correct o-rings for the head and base gasket. And thanks to Archmill for his offer and sending the gasket much appreciated.....After two run outs its looking oil tight again, and running really well. Very happy.
Now to rebuild my wheels...
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Nice job. 👍
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It’s not fine to have to take the engine out of rebuilt bike that has been painted etc. at least there are no seized bolts and screws to deal with. I had to take the engine out of mine again after just 200 miles. Had to split engine and get into the gearbox after a problem with it jumping out of 5th gear. Great news you got your oil leak sorted. Just need some descent weather now!
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Good work and nice feeling when you've corrected something with a thought through solution.
They aren't a complex engine, but with careful detail attention needed to ensure reliable running one of the largest parts.
Hopefully all set for getting out as better weather comes :)
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thanks for those comments, must admit relieved to see it work out originally as planned! and looking forward to the warmer weather 8) now completed the rear wheel rebuild with a DS spoke kit, a bit of surface corrosion on the original front rim, only lasted 55 years with a rechrome, prefer to keep original parts but looks like I need a new rim and spokes. this seems to good a deal on ebay? or its DS again?
https://www.ebay.co.uk/itm/235987950725?_skw=cb750+front+rim&itmmeta=01JNS4258KD90PTA83N7VGQWYM&hash=item36f1fa5c85:g:5oUAAOSwECpnaUAG&itmprp=enc%3AAQAKAAAA8FkggFvd1GGDu0w3yXCmi1eo%2FaGv%2FakHw5SvOj0qqiAJ6d8BwfgREDTKNY0d29SuCNritb0n385LRk0XdoVXgrq6lPfZcBrF8H%2BLJFNHOVpeayf3yUcp9K0BTvY4SgFAOK71xaCtzGs61hA3pyHYlJKFXhbwd1yZqlarfPKVl0rEe4pm9CW3Okq3mNlALuh0KQ6j6dO2fFPbiaQm%2BGa1d2K%2B2YJxeiFpacnqY%2BdVgiA7cOSRYCZ0HEU8uKNQWMEqIPpJyZvjpDPmwVyahOO3sToyB4ujcKEns4FPtj4Q4U3xav8pwnnePsksrmotGVfIng%3D%3D%7Ctkp%3ABk9SR7rUiKSuZQ
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Better to buy a DID rim from David Silver and stainless spokes from CWC. That one advertised on Ebay is a Takasako.
I'm pleased the engine is no longer incontinent 😁😁
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Ha funny you mention that this bikes given me the urge! ;) stainless would be nice for the extra cost, always liked the idea there’s more give in flexible mild steel spokes, did have a look at your eBay shop for parts btw, a see DS has 2 front DID rims, I’ll maybe give them a ring tomorrow.
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I think that every 750 I have owned eventually had rusty front wheel spokes, so when I rebuilt my F1 wheels it was stainless spokes all the way, never looked back since.
Cheers
Dennis