Weber head specifications as new
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can someone point me in the right direction to find OEM specifications on the Lotus twin cam Weber head?
i'm having an engine rebuilder/machine shop check mine, but need the original OEM specifications to check against. thickness, openings, etc.
thanks
TED
i'm having an engine rebuilder/machine shop check mine, but need the original OEM specifications to check against. thickness, openings, etc.
thanks
TED
TED
"Driving a Lotus is a triumph of bravery over intelligence." Stirling Moss
"TaylorMadeClassicCars" on WWW and Facebook
"Driving a Lotus is a triumph of bravery over intelligence." Stirling Moss
"TaylorMadeClassicCars" on WWW and Facebook
- tedtaylor
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The Elan shop manual has much of the info, particularly good instructions on how to remove and install valve guides, tappet guides and seats.
I agree with 2cams. There are engine builders in your area who speak Twincam. They may save you both grief and money.
Regards,
Dan
I agree with 2cams. There are engine builders in your area who speak Twincam. They may save you both grief and money.
Regards,
Dan
There is no cure for Lotus, only treatment.
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StressCraxx - Coveted Fifth Gear
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CLARIFICATION = I am not getting the head rebuilt, I just only want a machinist to inspect for cracks, pressure test, measure against factory specs (I don't have the equipment or knowledge) to ascertain whether it is a good head or boat anchor.
TED
"Driving a Lotus is a triumph of bravery over intelligence." Stirling Moss
"TaylorMadeClassicCars" on WWW and Facebook
"Driving a Lotus is a triumph of bravery over intelligence." Stirling Moss
"TaylorMadeClassicCars" on WWW and Facebook
- tedtaylor
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You would still be better off taking it to someone who has Lotus knowledge. They should be much better placed to know what to look for. The Lotus manuals were produced when the cars were new - i.e long before the experience of 50 years passing of time.
1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
1980 Ford Escort 2.0 Ghia
Peugeot 505 GTI Wagons (5spdx1) (Autox1)
2022 Ford Fiesta ST.
1972 Ford Escort GT1600 Twin Cam
1980 Ford Escort 2.0 Ghia
Peugeot 505 GTI Wagons (5spdx1) (Autox1)
2022 Ford Fiesta ST.
- 2cams70
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Take it to Sandy at Quicksilver.
Rob Walker
26-4889
50-0315N
1964 Sabra GT
1964 Elva Mk4T Coupe (awaiting restoration)
1965 Ford Falcon Ranchero, 302,AOD,9",rack and pinion,disc,etc,etc,etc
1954 Nash Healey LeMans Coupe
Owning a Lotus will get you off the couch
26-4889
50-0315N
1964 Sabra GT
1964 Elva Mk4T Coupe (awaiting restoration)
1965 Ford Falcon Ranchero, 302,AOD,9",rack and pinion,disc,etc,etc,etc
1954 Nash Healey LeMans Coupe
Owning a Lotus will get you off the couch
- prezoom
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prezoom wrote:Take it to Sandy at Quicksilver.
Sandy and his team are absolutely first rate. He stands behind his work.
Regards,
Dan
There is no cure for Lotus, only treatment.
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StressCraxx - Coveted Fifth Gear
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tedtaylor wrote:can someone point me in the right direction to find OEM specifications on the Lotus twin cam Weber head?
i'm having an engine rebuilder/machine shop check mine, but need the original OEM specifications to check against. thickness, openings, etc.
thanks
TED
The head depth, together with maximum permissible metal removal, is given in the technical data of the workshop manual. Mine says;
Small valve, 4.638" to 4.643"
Big valve, 4.598" to 4.603" (higher compression ratios)
Max. Permissible metal removal,
Small valve 0.045"
Big valve 0.010"
No doubt heads have been skimmed over the years and it wouldn't surprise me to find a BV head below the limit. Equally if someone is using the head for racing they might want a higher CR and skim more than these figures.
I'm not sure what else you can check. Flatness would be my first call and following that answer you'll have an idea of how much you'd have to remove and what that'll do to the CR.
The head diameter for inlet & exhaust valve inserts and valve guides are also in the same section of the manual, together with oversized items. You'd only need this if you're doing a complete overhaul though.
Brian
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UAB807F - Fourth Gear
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There are ways to compensate for a thin head in ways the factory never thought possible. Please send it my way though if you're going to bin it!
1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
1980 Ford Escort 2.0 Ghia
Peugeot 505 GTI Wagons (5spdx1) (Autox1)
2022 Ford Fiesta ST.
1972 Ford Escort GT1600 Twin Cam
1980 Ford Escort 2.0 Ghia
Peugeot 505 GTI Wagons (5spdx1) (Autox1)
2022 Ford Fiesta ST.
- 2cams70
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i have the workshop manual "technical data" page 4&5 where cylinder head is, but nothing about thickness.
thanks for providing.
thanks for providing.
TED
"Driving a Lotus is a triumph of bravery over intelligence." Stirling Moss
"TaylorMadeClassicCars" on WWW and Facebook
"Driving a Lotus is a triumph of bravery over intelligence." Stirling Moss
"TaylorMadeClassicCars" on WWW and Facebook
- tedtaylor
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Hi Ted
Attached is the spreadsheet I use for head rebuilds. The standard big valve column is the best data I have been able to assemble from multiple sources and measurement of actual heads. I don't know of any authoritative factory source for most of this data. The workshop manual has some, the Dave Bean Catalogue has some, most comes from actual head measurements and lots of thought. If you're machine shop cannot understand this then go somewhere else
The file is a .xlsx excel file but I have changed it to a .xls extension as the site software does not accept the later excel file extension. When you open you may get an error message but ignore that and it opens OK at least in my version of Excel.
cheers
Rohan
Attached is the spreadsheet I use for head rebuilds. The standard big valve column is the best data I have been able to assemble from multiple sources and measurement of actual heads. I don't know of any authoritative factory source for most of this data. The workshop manual has some, the Dave Bean Catalogue has some, most comes from actual head measurements and lots of thought. If you're machine shop cannot understand this then go somewhere else
The file is a .xlsx excel file but I have changed it to a .xls extension as the site software does not accept the later excel file extension. When you open you may get an error message but ignore that and it opens OK at least in my version of Excel.
cheers
Rohan
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rgh0 - Coveted Fifth Gear
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tedtaylor wrote:i have the workshop manual "technical data" page 4&5 where cylinder head is, but nothing about thickness.
thanks for providing.
You're welcome Ted.
The data is from a copy dated 1970 and with any luck I'll be able to upload the pdf of the relevant pages for your manual with this post.
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UAB807F - Fourth Gear
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I have an original Lotus head that I bought as new old stock - I took some figures from it before having any work done on it and they were as follows:
The head thickness was 4.635".
Inlet port size at carb end 1.530"
Exhaust port at outlet face 1.140-1.142".
Inlet valve size 1.530" (exactly the same size as the inlet valve).
Exhaust valve size 1.325"
Hope this helps.
(Photos below are after some work was done) :
The head thickness was 4.635".
Inlet port size at carb end 1.530"
Exhaust port at outlet face 1.140-1.142".
Inlet valve size 1.530" (exactly the same size as the inlet valve).
Exhaust valve size 1.325"
Hope this helps.
(Photos below are after some work was done) :
Last edited by promotor on Thu Aug 01, 2019 7:22 pm, edited 1 time in total.
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promotor - Fourth Gear
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Just as another reference for a Weber head.
These are the specifications for new SAS Weber head, "street ported":
New LM25TF Casting to original dimensions
Cam bore machined into head (No cam bearing required)
Inlet port machined and hand polished to 40mm Weber 1.3 diameter
Inlet Valve seat cut for 1.625 dia valve- (Inlet valve not included)
Exhaust port machined and hand polished 1.25 dia
Exhaust valve seat cut for 1.4 dia valve- (Exhaust valve not included)
Colsibro valve guides fitted finished for 5/16 valve stems
Combustion chamber machined and hand polished @ 4.640 head height
Standard spark plug 14mm
All core plugs fitted
Full pressure test prior to despatch
Head supplied fully machined with valve guides and valve seats cut, cam caps & cam studs
Valve seats are in sintered material suitable for unleaded petrol.
Interestingly the SAS inlet port size indicated is smaller than that measured by promotor (1.3" vs 1.53"), but perhaps measured at a different location. On the other hand the SAS exhaust port is indicated as bigger at 1.25" vs 1.14".
But, subsequently during build, my engine builder opened up both intake and exhaust ports to a larger dimension (unknown).
These are the specifications for new SAS Weber head, "street ported":
New LM25TF Casting to original dimensions
Cam bore machined into head (No cam bearing required)
Inlet port machined and hand polished to 40mm Weber 1.3 diameter
Inlet Valve seat cut for 1.625 dia valve- (Inlet valve not included)
Exhaust port machined and hand polished 1.25 dia
Exhaust valve seat cut for 1.4 dia valve- (Exhaust valve not included)
Colsibro valve guides fitted finished for 5/16 valve stems
Combustion chamber machined and hand polished @ 4.640 head height
Standard spark plug 14mm
All core plugs fitted
Full pressure test prior to despatch
Head supplied fully machined with valve guides and valve seats cut, cam caps & cam studs
Valve seats are in sintered material suitable for unleaded petrol.
Interestingly the SAS inlet port size indicated is smaller than that measured by promotor (1.3" vs 1.53"), but perhaps measured at a different location. On the other hand the SAS exhaust port is indicated as bigger at 1.25" vs 1.14".
But, subsequently during build, my engine builder opened up both intake and exhaust ports to a larger dimension (unknown).
'69 Elan S4 SE
Street 181 BHP
Original owner
Street 181 BHP
Original owner
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