I can now post the title of my thread, but I'm not able to put the text into the thread!
What's going off now?
I can now post the title of my thread, but I'm not able to put the text into the thread!
What's going off now?
Last edited by HonkyWhiteTrash; 25-09-2017 at 09:17.
Great question, depends on build spec. BDA, BDP, BDG, all different CR's, cams all come into consideration.
Then getting the correct springs.....
I'm also interested in specific answers.
James
I'll try again! I tried posting my original post again and Turbosport still doesn't like the text!
Basically my thread was questioning the spring load rates I've measured in an Atlantic spec BD I'm rebuilding - the springs are 235 lbs at full lift. The engine's a 9500rpm engine with approx 0.446" inlet cam and 0.400" exhaust cam.
Having done some further checks both inlet and exhaust valve springs give 235 lbs at full lift which is either a tremendous accidental coincidence or evidence of some care taken to build the engine correctly so I'm now of the opinion that these are likely to be correct.
It'd still be good to know other people's experience of spring loads on a similar engine despite me feeling more confident about the springs in question.
sorry i cant do specifics, but given 9500 then id say that spring pressure is probably about right
The thing that was concerning me was that in comparison a Lotus Twincam runs with about 210 lbs on the nose at full lift in a 8500 rpm race engine with much larger valves - per spring there is more weight for the valve to be brought to a stop so in a BDA with lighter valves I would have expect to see a slightly lighter spring.
I reckon a 225 lb spring at 9500 rpm in the Lotus would be about right so just couldn't see how 235 lb is sensible.
Perhaps it is down to the rate of acceleration/deceleration of the springs in a BD that makes the difference?
Even with the spark plugs out the engine is tight to turn over due to the springs (crank and pistons all turn nicely on their own). Starter motor is going to take a hammering!
Last edited by HonkyWhiteTrash; 29-09-2017 at 06:54.
8500 and 9500 are worlds apart in terms of controlling the valves though.
i have a 16v vag abf lump out there, we only rev that to 8, but that is on 220 lb springs, which i did quiery with the cam grinder because my thinking was it wouldnt need such stiff springs seeing thats more than i use on a pinto which goes to the same revs, but apparently not!
Some interesting food for thought there Graham. If I'm honest I wouldn't be able to spec a set of springs myself even if I did decide these are wrong! As the springs aren't marked clearly what they are I was hoping to be able to make sense of the spring rates to identify them but haven't been able to obtain any info.
Will keep up the search and ask questions next time I'm able to speak to a BD specialist or cam grinder.
Has anyone an idea what the rate should be on a 1700cc BDR and/or the original 1600 BDA (which i believe had single springs)
I'm asking as i'm going through this also. But the max upper range limit for the engine would be around 7500 to 7750 RPM. I was thinking 180lb single springs using a 350 lift cam at full lift.
James
The standard RS1600 and RS1800 engines use single valve springs with max pressure of 123 lb - those engines were limited to 6500rpm.Originally Posted by James Jordan
I've got some info from Cosworth regarding a BDB engine (1701cc and 200 BHP) that uses a BD3 cam which is 288 degrees (seat to seat) and 0.350" lift - interestingly the spec list states that standard valve springs are adequate for this cam upto 7500rpm (ie the limit of a standard cast iron crank). There's mention of making the fitted length slightly less (I guess to increase spring pressure) to between 1.250" & 1.270".
HTH
While we on the subject of BDA head and Cam tray. Can anyone identify this? I think it came with somer BDA part i bought.
Thanks
James
While we on the subject of BDA head and Cam tray. Can anyone identify this? I think it came with somer BDA part i bought.
Thanks
James
What size thread is it?
Looks like a head stud - one of two with bigger collar than the other eight - to locate the cylinder head.
Thats what i thought it was, Its 1/4 looks like UNC on one end and UNF on other. 2 7/8 long.
Any idea where i could get the other one?
Thanks
James
It's not a head stud then - far too short and not big enough thread. Studs are approx 7/16".
I thought it could be for these 2 locations (red arrows) it replaced the (bolt / dowel) with the UNC / UNF stud pictured and incorporated the locating 1015 dowel.
See picture
James
That's a camcarrier locating dowel. Used at each end of the centre row that holds the camcarrier to the head. Burton sell these.
Cannot see them at the Burton website but that's where I bought mine.
Do you know this company? They have them listed.
http://www.bdaengines.com/Prod4CastingHardware.htm
Burton do a Spacer the 1015 item. Yes I’m familiar with Burke sky, the sell the KAM developers parts.
Thanks
james
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