Misab plate failure

[Roy Gillett]

Hi

I thought I should post just to register what I think is an unusual failure on my +2's twincam. I was having problems balancing the Dellortos with a Carb balancer so finally checked for air leaks around the sandwich plates between carbs and manifold (Why is it known as a 'Misab' Plate??). Squirting Easystart round the joint caused the revs to rise so I was pretty sure I had a leak. On stripdown three of the four Misab plates had multiple small cracks in the grooves for the 'o' rings which were obviously affecting the seal. Has anyone come across this before. None of my Lotus chums have seen it before.

Four new plates and new 'O' rings and things are very different and it is running well again.

They never lose the power to surprize, these cars, do they!

Roy

[cliveyboy]

Hi Roy
I have had the same problem. The plates are cheap cast metal and not particularly well designed as the metal is too thin in parts.
Clive

[ardee_selby]

(Why is it known as a 'Misab' Plate??)

See: download/file.php?id=21015

Swedish company? M.I.S AB perhaps? (AB ~ Ltd ~ PLC ~ Inc)

Glad to hear of an easy-to-fix fault...

Cheers - Richard

[john.p.clegg]

It's obvious

Metal plates In between to Suppress Any viBration

John

[Elanman99]

I've never heard the term 'Misab' before but while I was wondering how to top John Clegg's wit, I Googled it. Now I know what they are I am even more confused!

The original plates Lotus uses were diecast and held two 'O' rings so presumably would have double the vibration absorption of these 'genuine' Misab manufactured plates? I think that genuine in this case means made by Misab, rather than being a Lotus specified part. (unless Lotus did fit them at some stage)

Is it the diecast type that cracks? If so I wonder what the cause is, its not exactly a highly stressed part.

Ian (just going into the garage to look at my forty odd year old ones)

[ardee_selby]

It's obvious

Metal plates In between to Suppress Any viBration

John

Might I Suggest Another Basis?

Is it not the rubber component (O-rings) of the "sandwich" that does the actual "suppression"? The plates merely locate their radial position.

Richard (Mis-Information Stated And Balderdash!)

[ardee_selby]

I wonder what the cause is, its not exactly a highly stressed part.

Ian (just going into the garage to look at my forty odd year old ones)

Fatigue fractures? Low load but high frequency cyclic stresses over extended period?

Richard

[Galwaylotus]

Link to MISAB website: http://www.misab.se/tillbmont.php?kid=4-140-353-355. This page doesn't show the version that came with my engine which is a thin plate with an o-ring moulded to the ID - sandwiching it so to speak with a rubber thickness of 5mm and plate thickness of 1mm. Like the one on this link http://www.fastroadcars.co.uk/shop/index.php?act=viewProd&productId=106.

[Chancer]

Yes, your last link is a genuine Misab plate, I think the OP has mistakenly referred to his ones as Misab plates.

Genuine Misab plates were brought out to resolve the exact problem that the OP has with whatever his ones should be called, that and the sucking in of the 0 rings under high vacuum and hence are the best solution for teh OP.

I had a manifold on a X/flow once that had grooves machined for O rings but I could never find any the right size so I solid mounted carbs using gaskets, very wrong I know but they were Dellortos and showed no signs of problems.

When I sold the vehicle the person checking it for the buyer recognised the manifold and told me he used to work for the company C&T if I recall, he said that they didnt have the money to tool up for the O rings so used something that was then commonn and available, Hoover Junior dust bag retainers!!!

I saw the vehicle maybe a decade later still running well with solid mounted carbs!!!

[Roy Gillett]

Mine are the type illustrated on the Misab website with a groove each side and two 'o' rings per plate. It was the base of the grooves where the metal was very thin where the cracks started and theyspread out from there.

As I understand it the 'other ' type have only one 'o' ring onto which both manfold and carburettor abutt. Mine that cracked were not like that.

Roy

[Quart Meg Miles]

Mine are the type illustrated on the Misab website with a groove each side and two 'o' rings per plate. It was the base of the grooves where the metal was very thin where the cracks started and theyspread out from there.

As I understand it the 'other ' type have only one 'o' ring onto which both manfold and carburettor abutt. Mine that cracked were not like that.

Roy

I don't believe you can make a single 'O' ring version unless it is in two parts with a loose centre to stop the ring being sucked into the manifold.

[Galwaylotus]

http://www.rallynuts.com/user/products/large/CSP001_600.png
Check out the photo of the Misab plate that uses a single O-ring moulded to a plate. This is what came on my car.

[Quart Meg Miles]

Can't argue with that! Looks a pretty fat "O" ring so may have enough strength to resist the inwards suck if the bolts go slack.

Edit: Ah, I note the words "moulded to the plate". That's cheating!

[Galwaylotus]

Can't argue with that! Looks a pretty fat "O" ring so may have enough strength to resist the inwards suck if the bolts go slack.

Edit: Ah, I note the words "moulded to the plate". That's cheating!

Take it up with MISAB, Sweden. Perhaps it's what Mark Donahue used to call the "unfair advantage"!