Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Johnny4428 on August 17, 2021, 10:32:32 AM
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Hi guys, after fitting of new pistons and rebore cylinders thanks to Julie and Trigger, I fitted and torqued down the cylinder head, backed off and torqued again, no problems all looking good. When I fitted the cam towers and tried to torque to the specified torque the threads seemed to strip without much torque at all. Well two, I tightened the rest by hand but wasn’t satisfied after fitting helicoils to two that was stripped. I am now convinced that there is some debris has found it’s way down the cam chain tunnel. So firstly I had to question how much torque I was actually putting on these bolts so ordered a smaller torque wrench that was hopefully more sensitive to lower settings. 4 to 18lb foot compared to 5 to 150lb foot. But having checked (very unscientifically) against the other the longer wrench 8lb setting wasn’t far off maybe just liable to slightly over torque. I don’t believe I had reached the specific torque before these delicate threads gave way. I must say there is something that is resonating in my head about helicoiling all these threads before fitting. (Trigger?) So onward and upward I will now dismantle again downed to cases and helicoil remaining threads clean thoroughly and assemble. I would probably be wise to get another head gasket?
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You are probably over thinking the debri ending up in the bottom end BUT, I would probably do the same.
I personally wouldn't have any issues with helicoils (had to fit them to the cam tower retaining threads on one of the 750's I've rebuilt - bolts were just pushed into fully stripped holes!) and for piece of mind, I would put a new head gasket on.
Hope everything goes ok.
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Back in the olden days I had to get quite a few of those helicoiled, they seemed pretty prone to stripping.
Cheers
Dennis
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You can use the existing head gasket Johnny as the engine hasn't been run.
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Thanks guys and Julie. I’m quite sure I hadn’t quite got the leverage applied before stripping difficult to gauge with that long lever, get a better idea with the shorter new wrench. The other thing is was the damage done before? Wouldn’t surprise me having witnessed some of the work done previously.
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The center bolts on the cam towers strip for fun and i always helicoil as standard. You have to be careful as some of the cam tower bolts are longer than the others. If you put them in the wrong hole then, they will punch out the bottom of the threaded holes and the head will leak oil. ;)
6 ftlb is ok for these M6 bolts and make sure the towers go on without the rockers in as, this puts pressure on the threads .
One thing i have noticed from your picture is : I thought you were rebuilding a K3 ? The head in the picture is late K1/ K2 head.
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Thanks Trigger yes was centre tower bolts that stripped. I knew it wasn’t the correct head because of the standard dowels/knock pins were too long. Interesting that it is a K1/K2 although it is a K3 as far as I know the plate is stamped late 72. I thought the head might have been a later k4 - K6. Yes I did notice that there was two different lengths of bolts in towers. Thanks for help!
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I'd go with Time-Sert, a tad pricey but more reliable...