tapered spark plugs

[Jez]

I will be having some work done on the engine of my MG Maestro 2.0i in a couple of weeks. The engine shop spotted that the current spark plugs are not the tapered type and they should be on the 1990 O series engine. I ordered a set on ebay that showed a tapered thread on the photos, however they too have turned up without the tapered thread. Can anyone please confirm if all O Series engines are fitted with a tapered spark plug hole on the cylinder head or where early ones different? Also what is the correct plug to use? I struggle to find much mention on part numbers to say if the thread is tapered or not. For those not understanding the issue here is a photo lifted from the www.

[E_T_V]

All mine are gasket type I believe. I've never rememeber seeing any plugs in rover engines that are the other type.

[E_T_V]

NGK list it as BPR6E as the correct plugs.

[Jez]

Ok, this is proving to be really difficult to pin down.

However, my extensive google research suggests the correct plug for the O series head should be BPR6EFS not BPR6E or BPR6ES. The difference being the taper thread and not the more common gasket. It seems the F means tapered thread, although please correct me if I am wrong! I have managed to find a set on ebay. Gasket spark plugs should not be used on the O series head, or at least the later ones like mine.

[Simon]

No, they are Unipart GSP 4452 fitted throughout the production run according to the Legacy EPC. In the online NGK catalogue it mentions BPR6E and BPR6ES and all online part number equivalency convertors refer to those two NGK part numbers. All compressible washer type.

[E_T_V]

That was what I thought. The difference between BPR6E and BPR6ES is a built in suppressor in the plug I think used for RF interferance reduction.

I've never come across a plug without a gasket type seal including my turbo.

[G Force]

No, they are Unipart GSP 4452 fitted throughout the production run according to the Legacy EPC. In the online NGK catalogue it mentions BPR6E and BPR6ES and all online part number equivalency convertors refer to those two NGK part numbers. All compressible washer type.

Hi Simon is exactly right here.
You have to go way back to the first generation of O series engines, before the generation of engines that we refer to as O series to find taper seat type spark plugs. The O series engines fitted to Maestro & Montego's etc. were initially known as O2 & have a totally revised cylinder head to the original O series, hence the introduction of washer type spark plugs. Taper seat plugs were found on the O series fitted to Ambassador, Ital, SD1 2L, TR7, to name a few.

[E_T_V]

Ahh you learn something new everyday! Didn't realise the old O series used those plugs.

[Jez]

Hi and thanks for all the replies. When G force says your wrong, you take notice! So I removed a plug myself today and after a good clean up of the plug seat, it was clear to see it should have a gasket plug, as all the replies has said. Sorry, I was only going by what the engine shop had said to me. The real mystery is why they got it wrong?