Lotus Europa Forums > Garage
821-30 Rebuild/Bent Push Rod
Fred:
The 821-38 S/N 0539 Valve Spring Story
As discussed earlier this build was a joint build between Renault USA in Springfield Oh, and me, in North Carolina. The Renault guys were twisting the wenches and I was providing “Lotus” knowledge. This motor is not on the road so there maybe future issues, I done not think so BUT!
The initial build surfaced issues with one head bolt not holding in the block. They like to run a 10ft/lb over torque and the bolt was losing torque when sitting overnight. After a number of trips to their machine shop it was fixed and the build continued.
The cam specs from the regrind see pictures
As can be seen the valve lift has increased to 0.434”. Unfortunately at that lift the valve springs started to float at a low RPM. The spring were removed and heated to 200 F and tested for strength. They were very weak.
So I started a search, over a three week period I could not find any OEM springs. Research was then started on vale spring specs on the internet. My guess was one of the 1960’s series European cars might be close or even use the same springs. The British valve trains looked similar so I took the valve/spring set to one of the shops in the area that specialized in old “Mature” British cars, Jags, MG, Triumphs, but not much Lotus work. This is one of those neat shops were the owner has been there many years and has two other guys and all they want to do is talk cars, and yes I would not call it a pristine garage just great work a great prices. They looked at the Renault valve and spring combination and pulled out an MGB head and said it look like an early MGB set-up. Turns out from 63-67 and onto 70 the MGB had dual Valve springs.
Below is from an MGB performance tuning manual: See pictures
Early MGB Service manual see pictures
The shop recommended I contact Moss Motors: https://mossmotors.com these guys are British car part people and have showrooms in Virginia and California although they do not list Lotus part if you can cross reference what you need there prices are ½ our Lotus suppliers.
I ordered two MGB valve spring kits:
Product Name Part # Price
SPRING SET, valve 423-430 $23.11
SPRING SET, valve, double, uprated (20%) 423-455 $51.99
Here are my measurements with a digital caliper, maybe off what you would get on a machinist table? See Pictures
The MGB retainer stem diameter is too large to use on the Renault valves we keep the OEM setup. Renault Springs/Retainer 63-67 MGB Springs
During the head rebuild it was decide to go with the standard MGB outer spring (Above) and because of the extra length of the MGB inner spring to use the stock Renault inner spring. If when we get on the road and if we notice early “valve float” limiting RPM we may go to the MGB inner spring also, or the 20% stronger MGB outer spring time will tell.
REMBER I am not on the road yet so cannot tell if we will have any issues BUT I do not think we will. Everything is running great with about 2 hours on the bench stand.
There was a lot more work done to get to the MGB decision but I just cut to the chase to tell you where we are.
Questions??
Thanks Fred
dakazman:
Thank you Fred , I have read your post several times . I will heed your warnings, and again I say
I know it takes time to put together a post with that much information concisely and to the point.
I’m sure I will have more questions about these 821 engines. Thank you again!
Dakazman
GavinT:
Hi Fred,
Lots of investigation going on there, obviously, so that’s good.
Does your third pic describe the Lotus 821 spring rates?
I ask because I don’t recall the Europa manual having the full spec. on the stock springs.
I’m curious as to how you determined the MGB springs as suitable. As far as I can see, there’s no mention of the number of active coils in your 2nd pic so presumably you deduced suitability from the rate given?
So, no coil bind issues, then?
Did you calculate seat and open pressures so as to be able to make a comparison with the stock springs?
Is it too late to obtain spring recommendations from Crane Cams?
Just a couple of other notes:
Be careful if you’re proposing to use the MGB retainers that the angle etc. of the collet seat is the same. Also ensure the MGB retainers will maintain the same installed height. Don’t expect alternative retainers to automatically do this.
Remember too that the exhaust and inlet valves on the Renault use different collets IIRC . . I have no idea why.
Fred:
Thanks for asking, I am sure I still have left out details.
I tried to answerer your questions and did it in bold type not to yell just to highlight the answerer.
Lots of investigation going on there, obviously, so that’s good.
Does your third pic describe the Lotus 821 spring rates?I ask because I don’t recall the Europa manual having the full spec. on the stock springs. The third picture is from an MGB manual NOT a Europa, sorry for the Confusion.
I’m curious as to how you determined the MGB springs as suitable. As far as I can see, there’s no mention of the number of active coils in your 2nd pic so presumably you deduced suitability from the rate given? The second picture from an MGB tuning manual shows active coils 4 1/2 on the MGB outer spring, secondly the physical measurements and side by side comparison (See picture 4) led us to believe we had a winner.
So, no coil bind issues, then? We measured springs at the full 0.434" lift and had adequate spacing, no coil bind.
Did you calculate seat and open pressures so as to be able to make a comparison with the stock springs? We looked at the MGB spring rate in the shop and felt it was a little higher but not excessive with this cam we were comfortable with just the MGB outer spring as the starting position. AS I mentioned above we still have a 20% over spec MGB spring set if we need more.
Is it too late to obtain spring recommendations from Crane Cams? Yes out of business for a number of years.
Just a couple of other notes: We did NOT and could not us the MGB retainer the MGB valve stem is to large.
Be careful if you’re proposing to use the MGB retainers that the angle etc. of the collet seat is the same. Also ensure the MGB retainers will maintain the same installed height. Don’t expect alternative retainers to automatically do this.
Remember too that the exhaust and inlet valves on the Renault use different collets IIRC . . I have no idea why.
It is my understanding that collets are different so you cannot mix up exhaust vs. Intake valves, however the retainers are the same.
GavinT:
All good, Fred.
It looks like I misread about the MGB retainers and misinterpreted that 3rd pic.
I probably need to drink more. :))
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