Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Johnny4428 on January 11, 2021, 08:34:27 PM
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Rebuilt the rear wheel new bearings, rim, spokes and tyre to put on the road this year. Too much oil leaks etc to run so tear down was the only option.
Tidy up time I think!
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Made a start on engine this afternoon. One rocker shaft with slotted end inwards??. Centre bolts under rubber pucks not very tight. Any tips on separating head from barrels? Don’t think it will be any advantage taking them off together still got to separate them.
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The threads under the cam towers are a weak thread, helicoil while apart ;) Make sure that all the tower threaded holes have a bottom to them. Common problem is owners put the wrong bolts in the wrong holes and punch the bottoms out which, cause oil leaks you will chase forever. The black bolts with 9 on the head must go in the middle and the shorter ones to the outside of the towers.
If you have all bolts, nuts and washers out of the head it should just pull off. That's if you have the front and rear M6 bolts out and the special bolts that are in the puck holes x 4 of those.
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Thanks Trigger. Yes tower bolts were correct. All bolts loosened including front and back. Wonder if someone has had a go at sealing up oil leaks, there was a lot of silicon on the outside of the joint between head and barrels. Problem is with these fragile fins you dare not lever or hit anywhere. I will check all these threads thanks.
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If you have the bolts out of the 4 puck holes then, it should lift off. If you have to hit the head, do it with a rubber mallet to the side of the fins front and rear to shock. If it is still stuck then, there is a point on the barrels to leaver the head and barrels off at the same time. Once off you can knock the head off from the bottom of the barrels with a lump of wood ;)
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Success with the separation this morning. It’s amazing an overnight rest with a bit more light too. New day and patience restored. Pics to follow when they upload to iPad.
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Bit of cleaning this afternoon old gasket surfaces. Pistons fitted wrong way around.
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This is not good, started taking some measurements today and the camshaft lobes are 4 - 5 thou below lower tolerances. So it is toast. Don’t suppose anybody has one laying around?
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This is not good, started taking some measurements today and the camshaft lobes are 4 - 5 thou below lower tolerances. So it is toast. Don’t suppose anybody has one laying around?
If the cam is that far out then, the follower must be fecked ;)
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Is it obviously worn on the tips of the lobe?
If not, it's possible it could have been ground on the base circle to "effectively" increase the valve lift.
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Yes you can see by the profile of the lobes it is worn. The followers didn’t appear to be bad to the untrained eye.
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Johnny, what number has that cam got on it? The number will be near where the sprocket goes.
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It’s an R8 Julie.
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I have no evidence to suggest this engine had been dismantled by previous owner other than the fact that there was one oil restrictor missing! There is minimal wear other than the camshaft lobes. Crankshaft is good main bearings big ends and small ends good, pistons and rings good. Scars on one or two of the mains so will replace them as well as primary and camshaft chains, tensioner etc. Maybe wounds from when the drive chain decided to break into the crankcase. The pistons are standard size Honda stamped, but why would somebody decide they were in the wrong way round? Bores very good no scores and no lip. So the stupid question is did the restrictor missing impact on the delivery of oil to the camshaft or did it deprive delivery elsewhere with the reduction in pressure?
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An oil restrictor missing would severely reduce oil presure to that side and cause damage quite quickly I would suggest. Also, you say pistons in wrong way round but not been stripped previously? Or do you mean not stripped by last owner?
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Yes the restrictor would potentially change which parts are showing wear.
It's there to hold the crank and big ends at full pressure, while not letting the camshaft bleed away to much of the oil supply.
In practice, and if the camshaft main bearings are good (they'd be recieving more oil than planned) their sealing isn't bad, and so this may have helped the crankshaft pressure stay up and so avoid significant wear. If it's got away with a little more wear to shell beatings, then that's not a bad outcome.
Obviously, putting back to new shells and correct restriction control should cover it off.
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Restrictor missing, the way i understand it, lowers the pressure at the crank causing shell/journal wear and to my mind would reduce flow on the side that still had the restrictor fitted as the oil will take the path of least resistance i.e. the "open" hole. Happy to be proved wrong though
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I have no evidence to suggest this engine had been dismantled by previous owner other than the fact that there was one oil restrictor missing! There is minimal wear other than the camshaft lobes. Crankshaft is good main bearings big ends and small ends good, pistons and rings good. Scars on one or two of the mains so will replace them as well as primary and camshaft chains, tensioner etc. Maybe wounds from when the drive chain decided to break into the crankcase. The pistons are standard size Honda stamped, but why would somebody decide they were in the wrong way round? Bores very good no scores and no lip. So the stupid question is did the restrictor missing impact on the delivery of oil to the camshaft or did it deprive delivery elsewhere with the reduction in pressure?
That engine has defiantly been apart before as, the PO would never of got all the broken bits out from the case damage ;)
With only one jet in, the engine would of destroyed the crank in no time. I have known owners to drill out the oil jets out to a bigger size thinking, that they would get better oil delivery to the cam. Yes, you do get loads more oil to the cam but, blow the crank out :o
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Thanks for comments, I only doubted the complete stripping of engine because of the nature of the repair! Over patched rather than repaired properly. All makes sense Bryan regarding oil restricted on one side that’s where there was slightly more wear when measurements were taken. Especially at the end of camshaft (No 4). Think I am reasonably lucky to come away with a good crank by the sound of it, and I am so glad I didn’t put this on the road this year without inspecting internals. I get Triggers logic in stripping even if it has been restored. No hiding place for “skeletons”.