23 replies to this topic

[Pigeonto]

Yup, my original '92 12G940 head has all 8 fitted with inserts

[A-Cell]

Factory unleaded heads have hardened inserts in the inlet and exhaust, but those aren't factory ones!
Get another head that's not been molested

[ACDodd]

And to add factory unleaded 12g940 heads on have inserts for the exhaust valves only.

Ac

[Spider]

All the factory heads for unleaded only had them in the exhausts, however if in manufacture a seat was 'not right' they wouldn't scrap the heads either, they would only then fit inserts from the factory.

[Spider]

Edit to my last ^

 

 

Woah there, factory 998 heads do have an insert for both inlet and exhaust valves.

Ac

 

 

When did they start doing this?  

 

Learn something all the time.

Edited by Moke Spider, 31 October 2015 - 12:09 AM.

[ACDodd]

1989, from the inception of the factory unleaded 998 head. engine number 99HE onwards.

 

AC

[Minitransition]

Thanks guys ! Hot topic and we have all learned sommat !

 

So - the engine and head (I thought were both original as they were mustard colour) are from a November 1989 Auto. The engine number is indeed 99HE21103540.

 

So - machine shop is checking that the other 6 will not pull out and is then fitting new inserts correctly to cylinder 2 whilst also replacing a corroded by-pass pipe. If any of the other inserts move when pulled I will declare time on this head and start again !

 

Could even be an original Rover / Mini tolerance ******* up from 1989 ?

 

The previous owner had clearly been trying to rectify a misfire as all new plugs, leads etc were fitted and as I mentioned cylinder 2 had carbon soaked in fuel - so I think I have found the cause ! I doubt an insert that can be lifted out with a finger nail would be gas tight !

[Spider]

1989, from the inception of the factory unleaded 998 head. engine number 99HE onwards.

 

AC

 

I did have a look following reading your post here, and there you go. Thanks.

 

I haven't dabbled intimately in small bore stuff for a long time, so I'm not up to speed with these smaller details in the later engines.

[Minitransition]

SOLVED !

 

Machine shop went to recut valve insert seats on cylinder with loose inserts and identified a minor crack which could not be seen prior to machining, see photo. Crack is between blue lines.

 

So - theory is exhaust valve crack generated overheating or hot spot which made other insert loose.

 

Glad I found it before re-assembly !

 

Thanks for all the advice - I find it useful if a conclusion is posted when known. New head purchased !!  DSC_0089.JPG   43.84K   16 downloads