misab plates

[Bob_Rich]

hi again 

 

in other earlier post  I got useful info re- fuel rating of hose --that was very helpful. I have now got the twin 40DCOE back in the car (S3 lotus 7 sprint spec crossflow)  and I was wondering how tight should the 8 bolts that hold the carbs be?  I assume a check with a feeler gauge should give a clue  see pictures attached below 

 

thanks in advance for any help

 

bob richardson

[Bob_Rich]

having trouble trying to upload the pictures so trying to add them here

bob richardson

[Miker7]

I don't think you can use a feeler gauge. They want to be tight enough to hold on the carbs, but not so tight the carbs can't move if rocked. The idea is they insulate the carb from the engine to reduce vibration and frothing of the fuel. If you can rock the carbs 10mm up or down, they're too lose. If you can rock them a few mm they're probably about right. An alternative view is the metal cups on the bolts should be squished so they're between 1 to 2mm apart.

[anthonym]

I just refitted mine and the eight nuts were all different tightnesses so the gaps were all different, consequently getting the mixtures right was impossible I now know. 
 

Feeler gauges no not really. I used a vernier caliper, the internal measuring legs, set to around 2mm from manifold face to carb face, using one corner that was already about that, then adjusted all others to match, which with that first gap fixed tight was easy (ish!) to do. The inner lower nuts can be difficult when all components are in place (Dellorto).

I will be checking them again per mike7 above.

 

Edited July 11 by anthonym

[Roger King]

Bob, your photo of the "cotton reel" bobbins looks about right. I'm afraid this isn't an exact science because the steel cups are not made to a precise and consistent dimension. Miker7's description is about right re. the amount you can move the carbs up and down at the air filter end so long as this is done without exerting significant force (yes I know that's really vague). Tiny air leaks are an absolute no-no at idle, but will have no significant effect at full throttle.

What you can do is to spray WD40 or similar over the Misabs when the engine is idling. If it makes a noticeable change to the idle speed or smoothness that suggests a leak (which the spray has temporarily sealed).

[Bob_Rich]

thanks for all the replies-- all useful info.

they do seen about right based on Miker 7 comments and supported  by most others posts

will try the WD40 trick when I get to setting up the idle

thanks for all the useful advise

cheers Bob

[Gridgway]

The rolling road people checked mine by rocking them by hand at idle and at a faster speed, say 3k rpm.  If it changed the rpm then it was too loose. 

[Bob_Rich]

thanks for that Gridgway  --I will give a try.

I am still struggling with it as I had started to sort it got it going  following a note form REDLINE (USA one)and went for a run about 20miles and then it started to shudder and misfire  and conked out and would not start.. while waiting for a mate to arrive checked fuel it was getting to the carbs OK.   when he arrived about 15 minutes I tried to start it burst into life and not entirely smooth but OK got home about 4 miles OK.

once home checked sparks all ok (see picture)  thought the rear carb was looser than the front  so tightened it a bit.  checked tappets a couple were quite a bit out ( based on Tony Weale Book setting for a sprint crossflow) also they are off a type that does not use lock nuts ( see picture) and a couple were very easy to adjust - - should they use loktite?  after this adventure  checked the plugs ( they were new !) they are really sooty (see picture).  Also checked the carbs  balance with a syncrometer and they were not too badly balanced. Checked the timing with a timing light and it seems about right  at a round 10 degrees BTDC but does not respond as I expected  when I rev the engine   (should it advance more?) distributor is one of the Lucas rally ignition units

Currently it starts OK runs bit lumpy but revs OK. A lot of spitting and  with some backfires. I have ordered a new set of misab and grommets and I think I might have to order some more tappets.

any further advise would be appreciated 

Bob

[Gridgway]

Have you put the plugs in the picture back in?  If so, try new plugs and I suspect it'll start and run fine.

The ignition timing should advance.  If it doesn't something is wrong.  The Lucas rally ignition is very unreliable, that could be a problem.

But overall it looks like it is running rich and fouling the plugs.  I am less convinced about the plates.

I'm no expert on the tappets, but if they are very easy to turn with no locking capability that's a disaster just waiting to happen!

If it were me, I'd get it to a rolling road session to get it sorted.

[7 wonders of the world]

Adjusters are self locking and require a fair torque to move them.

Spacer tubes would have been worthwhile adding but more importantly I would closely examine all the collects as I suspect you have no gap in yours... pretty common on x flows... this means they cannot fully grip the stem and can become dislodged leaving the valve in free fall.... destination piston crown.

[Gridgway]

Presumably "collets"?

[Roger King]

If you are running the standard valves with three collet grooves, which you most likely are if the engine is a Sprint, then the collets are sitting correctly, since they clamp against each other leaving the valve free to rotate (to even out wear). 

The plugs are a concern and as Gridgway says, the ignition should advance as the revs increase. Ideally, with an idle figure of 10 degrees you should see around 34 degrees at 4500rpm plus.

I don't know the age of your engine, but later ones were fitted with a God-Awful so-called "unleaded" distributor which was timed in at around 14 degree idle and only achieved about 24 degrees at full advance. If you have one of those, get rid of it and you'll see a major performance increase, although it appears that yours may be stuck, in which case you'll see a HUGE performance increase with a healthy dizzy. The above timing figures assume you have a fuel RON of at least 95 Octane. Any ignition system (even contact breakers) is better then the Lucas system that Caterham supplied as standard. You have one of these if your rotor arm has a slotted steel skirt attached to its underside. In fact, this may be the cause of your ignition problem because that skirt controls the ignition timing and frequently breaks loose from the plastic of the rotor arm causing timing havoc. Also the plastic of the rotor arm can wear where it slots onto the dizzy spindle, also causing timing havoc. Check the rotor arm to see if the steel skirt is loose and then fit the rotor arm to the dizzy to see if it is a snug fit and can't rotate loosely on the dizzy shaft.

Earlier Sprint engines had an A2 cam profile, but later ones just retained the standard Ford camshaft. The Ford camshaft has clearances of .014" inlet and .021" exhaust, whereas the A2 has .020" inlet and .022". Unfortunately, the two cam profiles have near identical lift, so telling which is which is difficult without a strip down. My best estimate is that the cam profile changed in the early 1990s if that is of any help.

Regarding the loose tappet adjusters, using Loctite is a bodge, but if the engine is for your own use (and not sold commercially) it can actually work quite well so long as you use a high strength thread lock and thoroughly degrease before applying it. Then set the adjustment quickly and leave to set, preferably overnight, although that is being hyper cautious. Check regularly at first to be sure it has held.

Your plugs are a disaster. It may be partially caused by a rotten ignition system (see above), but you need to check the carbs thoroughly, particularly the float height, the needle valve condition and the idle screw settings. It is of course possible that you simply have completely the wrong jetting. One other thing is the fuel pressure; you only need around 2psi. Too much and fuel can force its way past the needle valves causing the carbs to run rich.

Edited July 22 by Roger King

[Bob_Rich]

Hi All

 

A lot of useful info there-- Some I am not familiar with if  I am honest!  Refitted the carb with the existing Misab plates and when it spits back I can see the spit  back, by eye,  past  what appears to be a gap in the misab plate of number 2 cylinder.  Have ordered a complete new set of Misabs and the  attendant grommets.  As the carb will be off  I was going to look at the distributor, which with a timing light better shielded from ambient light does appear to show around  10 degrees before TDC at ~ 1000rpm  and does advance  as the engine is reved up.  The dizzy part number is 41964-59DM4  0606

is there any service info around for this dizzy?  As I understand it uses a normal mechanical advance   despite being electronic and magnetically triggered.  

thanks for all the help so far

regards

Bob

 

 

[7 wonders of the world]

I'm not sure I agree with you on that point Roger, the valve rotation is taken care of by spring resonance and the torsional deformation that occurs during compression and subsequent extention.

If there is clearance between the collects and stem this leads to fretting and the formation of burrs and ultimate failure.

 

[Roger King]

In many cases you are correct and this certainly happens with the valve material that Caterham used on the Supersprint (E214N I believe), but with the same three groove collet design that Ford fitted to standard valves). It was almost inevitable that these valves could not be removed from the guides, even after a few miles, without first grinding off the burrs around the collet grooves. That kind of valve material requires a single groove collet that locks firmly onto a single groove valve as well as its retainer so the valve has no free movement within the retainer. The standard Ford valves, which are a completely different material, use three collet grooves and matching collets that actually lock against each other and the retainer, but not the valve. They do not suffer from the burring problem. Indeed, you can fit a three collet groove valve with its retainer and collets and it will freely spin within the assembly. If a Crossflow was uprated to the extent that it needed the better valve material I used to fit single groove collets and valves (plus different retainers) so the burring issue didn't occur.

Edited July 22 by Roger King