Have searched forum for answer to this but no luck .
My early 18 has both heads with offset plug holes!

What can I replace them with to have central plugs bearing in mind hexagonal barrels?

I could get these filled and re profiled etc but its added expence.
Any aftermarket reliable ones?

I am doing this as part of total re build and considering all costs and wether its cost effective.
I looked at the 300cc conversion also a lot more dosh with pipes 2k ! and some queries on hail seizures too and as I thrash the bike round Silverstone gp a couple of times a year it must be sound ,
Any experience of 300 would be appreciated.

Fastfill

HRC made centre plug heads for both the 88 and 89 MC18's. No aftermarket ones were/are available.

Standard MC18 heads work well enough. They are effectively the same (well, very similar) to the rear MC21/28 head that's used as the HRC conversion on later bikes.
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Andy.
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Cheers Andy

Might get them filled later then and see if it makes a difference!

Just thought I might add that the reason I asked in the first place about the heads is that tuning section here says that "only mc 18 s have truly center mounted plugs"
Well they dont! not mine anyway! Am I confused I dont Know? maybe i am reading it wrong
The MC28 HRC kit is nothing more than a stock top head and different radiator hose, although special heads were produced for all other models, with the 1988 and 1989 MC18's having true centre mounted plugs.

Cheers fastfill

Only HRC MC18 heads have centre mounted plugs. I'll have to check... maybe it's not written clearly.
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Andy.
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The piece actually says, in reference to HRC parts:

"The MC28 HRC kit is nothing more than a stock top head and different radiator hose, although special heads were produced for all other models, with the 1988 and 1989 MC18's having true centre mounted plugs."

That is actually a little incorrect, as 1991 MC21 F-III heads are very slightly different to the stock heads, but the difference on their own would, in my opinion, be immeasurable.

And also, when looking at stock heads:

"There is no benefit in changing the MC18's head configuration."

Personally, I think that's quite clear, but it could still be worded a little better I guess.
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Andy.
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Oh yeah
It means hrc heads. Ta!!

Fastfill