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stripped oil feed threads in cylinder head

seeking advice yet again.......

i had a bad oil leak on one side and thanks to this forum i went through the usual diagnosis. fitted foo foo and checked with (LHM filled) homemade manometer that the vacuum was ok. then did a compression test. first i thought i had a problem as i was only getting 120psi when engine was warm. then i ran it for longer, until it was too hot to hold a hand on the rocker covers, then thanfully both heads gave the required 150psi (8.5:1 heads).

so, off with the manifolds and cowling and the problem was plain to see - a new spectacle seal fitted by the previous bloke upside down. sorted that and feeling rather pleased with myself until i stripped the thread on the oil feed pipe! aaaarrrrggghhh! whilst i have a slightly bent guage on my cheapo torque wrench, i'm sure it still did not get to 10 ft£.

Anyway, to the point, i can get a hold of a M7 * 1.0 helicoil kit, but is there any guidance on fitting these and particularly keeping the oilways free. i do not have a compressor but could i, say, inject oil with an old syringe to flush the oilways before reassembly?

any advice gratefully received.

Membership No. 1611

Re: stripped oil feed threads in cylinder head

There's a thread on here about stripped oil feed bolt holes - it recommends using a longer banjo bolt to pick up the remaining thread deeper inside the hole.

Re: stripped oil feed threads in cylinder head

Hiya Cye.

I did both mine in situ using grease on the helicoil drill and then used a small bore plastic/rubber pipe
taped into the crevice tool of the vac to suck out any debris. Same procedure when tapping the helicoil thread. A blob of grease on the tang removal tool when breaking the tang out worked well in that the broken off tang stuck to the tool. If you don't get the tang tool with your kit you can make one like I did. Use a bit of steel bar of suitable dia and cut a slot in one end face, this slot needs to be a snug fit on the tang in the helicoil. Trial fit before fitting helicoil to head. A gentle twist of the tool will break the tang and the grease should hold it to the tool.If the tang gets away fom you into the bore a pipe cleaner with a blob of grease on should pull it out. Regards Badger.

Membership No. 1462

Re: stripped oil feed threads in cylinder head

thanks geoff and gordon. i am taking both your approaches! i have a suspect thread on the 'good side' for which i'll maybe try the extended bolt, as there are clearly four or five threads which the standard bolt doesn't touch (i wonder why?). I have left a message with steve parrish asking whether he still has these available. if not i have one of his SS bolts (for the goodrich hoses, the longer double feed bolt) which looks long enough but would need modification for use on a head with standard oil feed pipe.

on the bad head I've just this afternoon fitted a helicoil broadly following gordon's advice. gordon, you must be a master keyhole surgeon doing this in situ - i needed to work with the head on the kitchen table. the grease idea worked well thanks. it certainly removed loads of swarf. i thought i'd just double check using one of those £5 optical fibre adaptors for a standard mini torch. lo and behold there was a big ball of swarf stuck up in above the area that I'd just tapped. a short piece of mig wire, again greased up fished this out.

the break-off tool that came with the kit is just a bar for hammering. instead i used a fine pair of long nosed pliers to break the tang, again with grease.

a good job. i will however, for belt and braces assurance, squirt in some oil using a turkey baster and allow it to drain back out through the newly tapped hole before refitting the head.

thanks to both of you for your advice, and thanks to Andy from NITS for lending me his M7 helicoil kit!

Membership No. 1611

Re: stripped oil feed threads in cylinder head

since the head is off the engine, would it be an idea to take it to a garage where they could use an airline to blow out any swarf?
Work from the valve side, fitting a plastic container over the valve spring, with a small hole in it to suit the blow gun.

Might also be an idea to keep the torque down, 7 to 9 lbf.ft is mentioned in Haynes, but since the thread is likely to be oiled, that really should be reduced to less than 7 lbf.ft.


Membership No. 724

Re: stripped oil feed threads in cylinder head

Thanks Ken but I'm only reading your advice now after I've refitted the head. I had toyed with the idea of modifying an old rocker cover so i could force oil in and get it to flow in opposite direction to normal, but then i realised i would have to plug up the pushrod tubes too and gave up on the idea.

i'll take a gamble and fire it up tomorrow night! i'll take the cover off again after a short run to make sure the head is getting oil, albeit not a measure of flow rate but i guess better than nothing.

just a thought, but wondering whether use of new double copper washers contributed in part to the stripping of the thread - after studying the old separate washers that i removed, it is clear the inner one was well bedded into the chamfer on the threaded inlet, and the bolt originally looks like it may have sat a thread or two further in.

i'm still at a loss as to why the bolts are not made longer as there's plenty of unused thread in that hole!

Membership No. 1611