This is one of the bypass hose adapters used, originally supplied by Mull Motif and which has a hexagon for tightening and undoing. In my opinion this is the best bypass hose adapter and can easily be removed with the head in place.
BM bypass stub.JPG (1000.25 KiB) Viewed 29865 times
Make sure that you use the correct 5/8" x 16 TPI tap to clean up the threads. The threads are not 5/8" x 18 TPI UNF as specified by some suppliers.
by-pass tap (1).JPG (1.13 MiB) Viewed 29865 times
This is the other type of bypass hose adapter but the screw driver slot (if fitted) is useless when trying to remove the bypass hose adapter from the head.
by-pass adapter (1).JPG (374.77 KiB) Viewed 29865 times
Here is the correct tap for the bypass adapter. It also suits the crankshaft starter dog/bolt. The tap listed is a good price. I paid considerably more for the tap featured in the photo above. https://www.ebay.co.uk/itm/363686649697 ... R6SfrJSqYg
As an aside - that blanking plug for the head horizontal oil gallery is not standard. I would check to make sure all is correct.
The plug is there to block the horizontal oil gallery which feeds up to the rocker shaft.
The plug should be brass. I suspect that someone has removed the original brass plug to examine or unblock the gallery.
If it not leaking I would leave well alone.
svenedin wrote: ↑Thu Jul 13, 2023 9:50 pm
Yes it's for the bypass hose. I believe it does screw out but be careful you don't snap it. I'd soak it for several days in PlusGas before trying!
You can use the original length part or a longer part which means a new bypass hose can be fitted more easily without removing the cylinder head.
I bought one of the hex-type adapters from Bull Motif but they actually sent a one without a hex-nut! Apparently they have been misleading people for 3-years by showing a hex-nut image on their website but sending items with the slot. Not impressed with them.
Following up on this thread for the interest of anyone interested....
I put the head in to a local engineering place about 3-weeks ago. A good lad who has a workshop full of expensive machines, a Lola racing car and a Lotus Europa so I think he must be somewhat familiar with English motors. Then again, the Europa has a Renault lump so maybe not.
He got the bypass adapter out for me (which I managed to make a pigs ear of with the mole grips) and changed the valve guides. Unfortunately me being a bit dim witted I failed to notice the non-original head before I bought the new valves. Meaning I have a set of valves for a 950cc head which are too small for the 1098 head I gave him.
I took the old valves to him yesterday and he said that he'll try and see if they can be worked on to be re-used. They were a bit pitted as shown in another thread I put on here a while ago and the end of the stem may be damaged due to angle of the rocker not pushing directly downwards on them. I'd never have thought about that myself. If they can't be machined then I'll be buying some new ones next month.
I did buy a cheap 12A1456 head the other day anyway so I will at least have new valves for that when the time comes.
One careful step forward at a time is better than one step forward and two steps back! Ask about the detail if not totally sure, before buying parts, etc, and you will get help to point you in the right direction quite quickly.
At least your posting might help others and prevent them making mistakes, so well done. You are progressing now.
I've had a look on ESM and the hardened exhaust valves they sell state they are for 803/948/1098 How can they be the same size for all engines?
I suppose I'll have to call them to find out what is going on to avoid buying the wrong valves again. It could be that the seats in the head have been enlarged. The head is a 12G202 from an 1098 - just a confirmation that the standard valves are larger than the 948 would help, in case anyone knows.
I would prefer to keep the 1098 head in the hope of getting a couple of extra ponies but now I'm starting to wonder whether I should just put an original one on - that will at least set it back to an original condition.
rocco wrote: ↑Tue Oct 17, 2023 7:22 pm
I've had a look on ESM and the hardened exhaust valves they sell state they are for 803/948/1098 How can they be the same size for all engines?
I suppose I'll have to call them to find out what is going on to avoid buying the wrong valves again. It could be that the seats in the head have been enlarged. The head is a 12G202 from an 1098 - just a confirmation that the standard valves are larger than the 948 would help, in case anyone knows.
I would prefer to keep the 1098 head in the hope of getting a couple of extra ponies but now I'm starting to wonder whether I should just put an original one on - that will at least set it back to an original condition.
As far as I know the exhaust valves are the same for the 948 and 1098 but the inlet valves are NOT the same.
Did you fit the valve guides with the groove for the newer "top-hat" valve stem oil seals?
Stephen
1969 1098cc Convertible “Xavier” which I have owned since 1989.
rocco wrote: ↑Tue Oct 17, 2023 8:47 pm
Yes Stephen, I bought the grooved guides that Phil recommended and they were fitted last week.
I will check with the mechanic again but I saw him measure and compare one of the valves and there was a visible size difference.
Well the 1098 inlet valves are larger than the 948 ones.
Thanks. So the exhaust valves are the exact same size? I know I should have compared and measured them myself but it just didn't register with me, even once I had identified the larger head.
How can they be the same size for all engines?
