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CIH exhaust valve seat width??


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Help please.

I've cleaned up my cylinder head and lapped the valves in. When I've done this in the past I've not given much thought to the contact width of the valve seat. Anyway, I've measured the width and compared it to the Haynes manual and they are considerably bigger. On top of that, the exhaust seats have still got some small pits even after being lapped a couple of times. The problem is, the more I lap, the wider the seats will get. This head is not unleaded so I've compared it to a 2.4 head I have lying around which I think has hardened valve seats. I just did a very quick lap to clean them up and the seats on the frontera head are much narrower. The question is, am I being too fussy?  Or does the head need machined? Or is it time for hardened valve seats/unleaded head?

2.0 exhaust valve seat.


2.4 frontera ones for comparison.


I'm not trying to use the 2.4 head I just bought it for the aluminium rocker cover.

Thoughts please. I'm not trying to make anything fantastic....I just want it to work.

Thanks in advance.

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lapping the valves in with paste wont have widened them significantly so i wouldnt worry. 

the seats are totally bare metal now with no lead memory/ coating so you would be wise to use an additive although i have run non unleaded heads on unleaded with no ill effects .the standard 2 litre unit is not classed as a high performance engine and is relatively unstressed realy. ive used a 1256cc viva unit for 10 years and 5000 miles without having it converted.

obviously in an ideal world hardened valve seats is the way to go but ive had a few heads converted locally and not been totally happy with the finished job .this depends on how much you trust your own choice of machine shop to do the work but in my opinion you would be better getting a proper gm unleaded "P" head as you will at least know it will be correct .

if you are running a 20s then the perfect choice is from a mk2 85-86 carlton 2 litre (carb) or if you are on injection then a gte head will be readily available on here i would imagine.

seeing as the head change on these cars is only a couple hours or so i would be tempted to just refit your head and use it .

how much mileage are you planning per year ?

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Many thanks, really appreciate the response. 

This engine is just to get me going and as the whole unit is unknown to me I wasn't wanting to spend a fortune so I'll go with refitting it and see how I go. I've never bothered measuring seat width before and never had any bother. I've just been watching too much YouTube probably.😃

The engine is injection and going in a manta. Thanks for the advice on using an additive, I never considered that I may have removed the built up protection.  This is car number 4 so I'll only do 1000 miles a year probably.

My long term plan is to use the valves from the 2.4 in a 2L head on a 2.4 bottom end but this is just a pipe dream at the moment and I'm still researching.

Thanks again.


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The car is an 81 SR coupe but I bought it as a shell, no engine gearbox, interior etc. I bought the engine from someone with an exclusive who is putting a 20XE engine in so I thought the engine was a late one. When I checked the block number and head stamp it's an early engine so something has been swapped along the was. The engine wasn't expensive and came with loom, manifolds, ECU etc so I've no complaints but it was leaking oil from all over, the water pump is leaking and there's no thermostat in the housing so I'm not wanting to throw money at this engine at the moment. I've checked the big end and main bearings and they look ok so the plan is new gaskets, water pump, thermostat, belts etc and see what it does. 

I read in an early post that it's a good idea to have an engine in the car that works while you have one on the stand that you build, and I like that idea.

I'd like to get it on the road next year for its 40th so I better crack on....


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Just for peace of mind:

Opened once a 1.9 Manta A engine that runs on LPG. Rebuilded the head so I could fit stemseals. The valve seats were still good and after lapping the valves no damage found. After rebuilding the engine I checked the exhaust and noticed the LPG setting was too lean and tuned it a bit till it was rich enough. 

Those old cast iron heads are not that fragile, by the way: nice looking chassis.

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Many thanks. It's getting there. That has a coat of etch, a coat of red oxide and 2 coats of black but then I decided I wanted the underside to contrast the black running gear so I mixed some dark grey and it's had a coat of that.   I'll do an update on the build soon.

I was just a little concerned that someone in the past had maybe done something wrong as the seats are about 50 to 100% too wide. The heads definitely been apart before. It has bronze valve guides  and the tops of a couple of the valves were a little scratched up where someone has struggles to remove the collets I think. The little bit of pitting I couldn't remove from the exhaust valve was also a concern. 

I'm happy to clean it up and put it back together. I'll put a spark plug in the head and make sure the valves hold petrol before I put the head back on. 

Have a good weekend both and thanks for the responses.


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it will be fine. ive stripped many a head to do an overhaul on a seemingly good running engine with good compressions and found slight pitting like that and has been fine. yes in an ideal world you would get them to an absolute perfect surface but that would mean grinding them down even further and can be done but takes time and makes the seat even wider. 

make sure the stems are not too loose in the guides and that the rotator cups are not seized.camshaft should be fine (very early ones used to wear lobes)and that the followers are flat and ok ( but any slight curving sholdnt matter too much especially if they go back where they came from)

if you are realy concerned then go a bit further or obtain a later 'P' head .

but for the mileage you intend and to get it up and running i would just rebuild it and fit it 

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Thanks again for the advice.

The guides seem ok. I think they have been replaced at some point as according to the Haynes manual they weren't brass originally. Anyway, almost no play but valves glide up and down fine. The hydraulic follows all seem flat and are shiny. Camshaft look fine too.

Like you suggested I'm going to but it back together. Just need to clean up the block now and replace all the gaskets and seals and then I'll crack on with the bodywork.



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