Possible head off

herbie

Member
Hello all,

Replaced fuel pipe and added filter after dragging a load of muck up as mentioned previously.

Rebuilt carb, replaced leads, plugs, points condenser, cap, set timing, colourtuned carb.

Still misses on idle and pulling number 3 lead has little effect compared to the others.

Compression test 120 on all 4 which seemed a little low, but number 3 was the same as the others.

Have checked for air leaks as best I can, sprayed easy start around carb when running and I don’t think I can detect revs climbing.

Off with its head? What do you think?

best wishes,

Richard.
 
Were the compressions tested warm with the throttle fully opened and a fully charged battery? It your starter motor tired? A leak down test would be a good idea I think. Eliminates other reasons for low numbers.
Since your numbers are very even this is generally good. Also what is your compression ratio? They can be set up as low as 7.5 : 1
 
Not really warm as such (the weather certainly was) starter motor is not the quickest, battery ok so possibly room for a bit more pressure, throttle open cranked for about 6 revolutions.

not sure on compression ratio, engine is a genuine 60,000 mile one and has been looked after well.
 
I’d add to James’s comments by saying once you’ve done his suggestions drop a little oil in each cylinder and rerun the comp test. If they climb dramatically it suggests tired bores and rings.
 
Not really warm as such (the weather certainly was) starter motor is not the quickest, battery ok so possibly room for a bit more pressure, throttle open cranked for about 6 revolutions.

not sure on compression ratio, engine is a genuine 60,000 mile one and has been looked after well.
That doesn’t sound like a wear issue. Have you checked for a spark on all leads?
 
Check the valve clearances, a tight one could make it miss on idle and come on to 4 as it's revved, until higher revs, when it will gradually start missing again.
 
Yep definitely got a very health spark on all leads.

Interesting about valve clearances Harvey, the car when it’s going goes so well, for a 2200 sc auto it holds its own and regularly does long journeys abroad and from London to the West Country.

Assuming the manual will have a method for the valve clearances, I’ll go and dig it out.
 
Leave the car overnight and then check when it's stone cold the next morning. It's worth checking them to eliminate them as the cause if nothing else.
 
Had a quick look this evening and number 3 exhaust valve clearance is nil!

Will have a proper measure of all the others and make a note of all measurements when I get a minute (have a 4 year old and 2 year old so minutes are sacred!!)

No. 3 is the cylinder that has the least effect on the engine running when the lead is removed.

Will it be difficult to see what shims are needed if the valve clearance is nil?

Thanks guys.
 
Will it be difficult to see what shims are needed if the valve clearance is nil?

You need to measure the shims that are in there, subtract 14 thou from that figure, fit those then measure the clearance and work from there once you actually have a clearance value.
 
Thanks Harvey, that makes sense. Is this lack of clearance likely to have done any damage do you think?
 
I guess the plan now is measure them all properly (the ones that have a clearance) as work out the shins needed and get spacers for the head bolts. Anything else I would need to do in preparation to getting it done?
 
I guess the plan now is measure them all properly (the ones that have a clearance) as work out the shins needed and get spacers for the head bolts. Anything else I would need to do in preparation to getting it done?
I used some large nuts as spacers when doing this, normally works well.
 
index.php
 

Attachments

  • IMG_0191.JPG
    IMG_0191.JPG
    1.5 MB · Views: 47
Back
Top