Head different
- Thread starter johan
- Start date
I had a look at the heads I am doing at the moment and cannot see a difference
this head shown first is a 76 head, it has been built using 40.5mm Kibblewhite Black Diamond inlet valves and Subaru Turbocharged exhaust valves, 35.0mm
Exhaust valves, exhaust ports and combustion chambers have all been ceramic coated
this next head is an RGS head, is actually Renata's head if you follow some other threads
I have made the valves for this head plus a full spare set and they are same as the 76 head, 40.5mm inlets and 35.0mm exhausts, not done the valve seats or changed valve guides yet
looking at the two heads I am stuffed if I can see any variation in the position of the valve seats to the spark plug holes
RGS head is marked 683
did they change after June, 1983 ?
this head shown first is a 76 head, it has been built using 40.5mm Kibblewhite Black Diamond inlet valves and Subaru Turbocharged exhaust valves, 35.0mm
Exhaust valves, exhaust ports and combustion chambers have all been ceramic coated
this next head is an RGS head, is actually Renata's head if you follow some other threads
I have made the valves for this head plus a full spare set and they are same as the 76 head, 40.5mm inlets and 35.0mm exhausts, not done the valve seats or changed valve guides yet
looking at the two heads I am stuffed if I can see any variation in the position of the valve seats to the spark plug holes
RGS head is marked 683
did they change after June, 1983 ?
breganzane
Hero member
- Location
- NSW Australia
Red,
Strewth - turbocharged exhaust valves! That thing is going to f-l-y!
Steve B
Strewth - turbocharged exhaust valves! That thing is going to f-l-y!
Steve B
Red,
Flip 'em over and inspect the edges of the cam cover mating surface.
You will find slight scallops to accomodate a plug spanner. My guess is the plug angle was altered to gain a little meat between the plug thread and the valve seat.
The same plug spanner will slip into the plug recess on the old head without coming close to the edge of the cover surface.
Too fuckin' cold here, or I'd dash over in the workshop and take a pic for you.
piet
Flip 'em over and inspect the edges of the cam cover mating surface.
You will find slight scallops to accomodate a plug spanner. My guess is the plug angle was altered to gain a little meat between the plug thread and the valve seat.
The same plug spanner will slip into the plug recess on the old head without coming close to the edge of the cover surface.
Too fuckin' cold here, or I'd dash over in the workshop and take a pic for you.
piet
Laverdalothar
Hero member
- Location
- Germany
Mmmh - would be a great thing if someone could make some photos of all various type of heads that have been built and mark the differences on the photo. Or a tabular overview with all the specs like:
.......................................1973 - 1974.....1975 - 1978.....1978 - 1980.....1981 - 1982....1983 - 1988.... Corsa....specials...1200...
Inlet
Exhaust
intake port
exhaust port
special casting differences
anyone up to do that? Maybe Red and Piet are the best for the info, I would be willing to do the tabular and put it into PDF. We could then post it here and maybe on JLO's page...
.......................................1973 - 1974.....1975 - 1978.....1978 - 1980.....1981 - 1982....1983 - 1988.... Corsa....specials...1200...
Inlet
Exhaust
intake port
exhaust port
special casting differences
anyone up to do that? Maybe Red and Piet are the best for the info, I would be willing to do the tabular and put it into PDF. We could then post it here and maybe on JLO's page...
okay, I flipped the heads over and took some measurements, it is not cold here, +30C today.
Early head is now a 75 head that we have welded but not machined yet, the original 77 head shown below is now wrapped up in gladwrap ready to install.
I used two of the mandrels that I made for my spark plug fixture, machined threads on chromed ground bar so I know they are straight.
Use these to clock up the angle of my milling machine head when machining new spark plug holes.
First photo is now of the 75 head, no cutouts around the area where the spark plug spanner goes through, on the left hand rail.
Measuring the right hand side between the mandrel and the edge of the rail I get 6.76mm gap.
this is the same RGS head, on this head I get 6.87mm gap to right hand side, opposite to where the cutouts are, right hand rail
there are a number of detail changes between the two heads, that is very obvious and I'd say the 120 head is a lot better product
the above measurement only checks the position of the spark plugs in one plane, when I get a chance I'll clock both heads on the milling machine and see if the spark plug angle has changed
would presume the 120 head is steeper as the inlet valves are larger hence would need to move the base of the spark plug hole away from the spark plug
maybe
Early head is now a 75 head that we have welded but not machined yet, the original 77 head shown below is now wrapped up in gladwrap ready to install.
I used two of the mandrels that I made for my spark plug fixture, machined threads on chromed ground bar so I know they are straight.
Use these to clock up the angle of my milling machine head when machining new spark plug holes.
First photo is now of the 75 head, no cutouts around the area where the spark plug spanner goes through, on the left hand rail.
Measuring the right hand side between the mandrel and the edge of the rail I get 6.76mm gap.
this is the same RGS head, on this head I get 6.87mm gap to right hand side, opposite to where the cutouts are, right hand rail
there are a number of detail changes between the two heads, that is very obvious and I'd say the 120 head is a lot better product
the above measurement only checks the position of the spark plugs in one plane, when I get a chance I'll clock both heads on the milling machine and see if the spark plug angle has changed
would presume the 120 head is steeper as the inlet valves are larger hence would need to move the base of the spark plug hole away from the spark plug
maybe
D
Davo
Guest
I'm either getting old or perverted or both, but that '76 head looks just plain sexy with that lovely ceramic coating. :-[
Scrumpy
Hero member
I have a couple of heads sat here in front of me. The clean one is stamped 180 so Jan 1980. This has a crack where Red has stated in his earlier post. It also has an S stamped on the front of the cam tunnel. The second head sprayed black is earlier and does not have the cast iron skulls, this is stamped 27, guess they did not stamp the last digit.
The earlier head does not have the locating lugs for the cam bearings where as the later head does.
The older head looks like it might have been skimmed. The machined area where the studs are located increases in size as you move across the head from left to right. Is this typical or the head not seated correctly when skimmed?
The older head has score marks where the buckets sit. It appears that some debris has scored the housing as the buckets have rotated. Is it possible to repair or clean this damage up or does the head need machinig and bigger buckets fitted if available?
Cheers Scrumpy
The earlier head does not have the locating lugs for the cam bearings where as the later head does.
The older head looks like it might have been skimmed. The machined area where the studs are located increases in size as you move across the head from left to right. Is this typical or the head not seated correctly when skimmed?
The older head has score marks where the buckets sit. It appears that some debris has scored the housing as the buckets have rotated. Is it possible to repair or clean this damage up or does the head need machinig and bigger buckets fitted if available?
Cheers Scrumpy
Hey Scrumps,
Measure the overall head thickness, should be ~94.0mm, if it is not then head has been skimmed.
Hard to comment on the score marks in the lifter bores from the photo, I'd guess you could clean them up and reuse especially as majority of the bore will be in gauge
will act as extra lubrication grooves
Measure the overall head thickness, should be ~94.0mm, if it is not then head has been skimmed.
Hard to comment on the score marks in the lifter bores from the photo, I'd guess you could clean them up and reuse especially as majority of the bore will be in gauge
will act as extra lubrication grooves
Both look pretty old to me, Scrumps!
Earlier head will need dowels over the M8 studs to locate the cam bearings. Oversize buckets are available should you need them. Scoring is rarely so severe to warrant a re-bore though.
Got an "S" marked head on the bench at the moment, has large exhaust ports, ie, no step before the header recess.
piet
Earlier head will need dowels over the M8 studs to locate the cam bearings. Oversize buckets are available should you need them. Scoring is rarely so severe to warrant a re-bore though.
Got an "S" marked head on the bench at the moment, has large exhaust ports, ie, no step before the header recess.
piet
Well, you learn something new every day...oversize buckets?! never heard of that before....hope never to need them. I had a head I paid fair money for which looked great...but I failed to notice it had been skimmed unevenly, and it now sits in Slaters display engine (or did last time I looked..)
Scrumpy,stop buying that junk and spalsh out on a decent one, eh?
Nick7
Scrumpy,stop buying that junk and spalsh out on a decent one, eh?
Nick7
tom3c75
Hero member
- Location
- Cape Town South Africa
I've just noticed that the head on my 1980 Jota has the plug scallops.
Does that mean it is an RGS head?
The head is still fitted to the barrels, so I can't see any stamped numbers.
Does that mean it is an RGS head?
The head is still fitted to the barrels, so I can't see any stamped numbers.
tom3c75 said:
no, it is probably a 1980 head
when I checked the heads that I have in stock the other day I noticed that the 1980 and 1981 heads I have all had the spark plug scallops to some degree
even some of the early all alloy heads had the scallop to a small degree
I have 17 heads here in various states of repair that I can use to compare at the moment
P
poffer
Guest
Stefan,
Glad you saved that from the bin.... I've got one of those in the garage that came attached to my early 3c. On mine, the camblock location is a bit random, so I have replaced it with an RGS one. Good luck sealing those rubber socks! (got 3 here somewhere if you need some).
Pete
Glad you saved that from the bin.... I've got one of those in the garage that came attached to my early 3c. On mine, the camblock location is a bit random, so I have replaced it with an RGS one. Good luck sealing those rubber socks! (got 3 here somewhere if you need some).
Pete
hochkoenig
Senior member
- Location
- Salzburg-Austria
nick7 said:Well, you learn something new every day...oversize buckets?! never heard of that before....hope never to need them. I had a head I paid fair money for which looked great...but I failed to notice it had been skimmed unevenly, and it now sits in Slaters display engine (or did last time I looked..)
Scrumpy,stop buying that junk and spalsh out on a decent one, eh?
Nick7
There must be some buckets from Japanese, but can?t remember what model... anybody knows that?