spitting back and won't run!

[willipig]

Being quite new to the OHC engine, can anyone suggest what's wrong with UR4313?
It was running well, then suddenly , luckily 400yards from my house, it suddenly lost all power, would only idle but not rev or pull and constantly spits back badly through the carb, unburnt petrol vapour being ejected, spitting back when idling every 2/3 seconds, worse when you try to rev....However, it will restart from cold (or hot) but with exactly the same symptoms...I have checked the following.....Ign timing and gap is spot on, coil and condenser have both been substituted,plugs and sparks all ok, carb stripped and cleaned( wasn't dirty) piston rises cleanly but flutters violently when engine runs, petrol checked and ok..no dirt or water in it, wiper vacuum bleed pipe ok.....OK, looks(and sounds) like valve timing has slipped, but on a visual check, seems ok...dynamo yoke appears directly across the car when No 1 piston on tdc on firing stroke but hard to be exact....can valve timing suddenly slip a bit, enough to cause such symptoms, yet not enough to stop car idling? Have I got to take rad off,dynamo out and check bevels etc, or am I missing something and could it be something else altogether? What visual checks can anyone suggest before I get to serious dismantling? Some urgency as it is entered in VSCC LCES rally at end March....Thanks, Bill Piggott

[Ian Grace]

Good morning Bill,

Welcome to the Forum - and glad we managed to overcome your registration difficulties.

Have you taken the cam cover off? It is not likely that the valve timing has slipped, as the various bevel gears are pretty well held in place, unless a major derangement has happened. I had a similar event happen to me (funny enough, in a fabric saloon) at the VSCC Jubilee Light Car Rally - it was caused by a broken valve spring.

While you have the cover off, you can double check the valve timing - when No. 1 is at TDC , the pair of lobes for No. 1 cylinder should form a perfectly symmetrical upright 'V' as viewed from the front.

Hope this helps,

Ian

[Ronald]

Bill, do a compression check...... sounds suspicously like head gasket failure to me...... sorry to say!

[ColinWLee]

Hi Bill.
Yes, I had exactly the same problem.
I found the head gasket had disintegrated between cylinders two and three, so they were "sharing" each others' compression, exhaust etc.
I replaced the gasket and the car was back to normal.

[willipig]

Thanks Gents for your very useful input....Ian Grace was nearly right...turned out to be a broken rocker shaft right at the back operating (or not!) no 4 exhaust valve...shaft totally sheared through...Spoke to Mike Dowley who says this is a common problem on these "small cam " engines, and they always break just there, 2inches from the rear...He hasn't got one in stock, but will make me one for next week, as it is a part he machines himself...luckily he is just up the A49 from here in Ludlow...
Have checked the compressions....70/75psi on cyls 1,2 and 3....seems a bit low, albeit even...is 75psi about right can anyone tell me? Bill Piggott

[Ian Grace]

Bill,

This is a weak point and Mike does a very good mod. which involves bolting a bronze support casting on to the rear pair of head studs and elongated rocker shafts which engage with it so there is no overhang behind the original rear rocker shaft support - which he might have in stock.

Ian

[ColinWLee]

The symptoms you described were the same as i had, so i was convinced your head gasket had blown between cylinders.
Isn't it amazing that the same symptoms can be produced by completely different faults.
Glad you sussed it though.
See you in Wales