Engine goes bang

[P3Steve]

Just what you need at the start of a season, Took the Rover out for a pre seasion run today as Ive been off all this week and have been local so have been using it all week as my daily just to make sure every thing was all right. Parked it on my high street and when I came back to it about an hour later it started but with a clatter and a misfire, stopped straight away and got my daughter to tow me the mile home with her 4x4. when I got home I pulled the plugs and disconected the fuel pump - it turned free enough on the starting handle with no tight spots but a slight knock/clatter was heard when it was spun on the button. I need to borrow a compression tester (mine is broken) as I think/hope it might just have "dropped" a valve or lost the head off one (with the rocker cover off all the stems for the inlet are there) - will know better when Ive done the test, I dont think its the bottom end and with a long thin screw driver down each bore in turn and turning it over on the handle all the pistons seem to rise and fall uniformly so I dont think its a con rod. will keep you all informed on the progress. pitty its always been such a sweet engine.

[Paul Gregory]

Very sorry to hear this Steve. I hope you manage to find the problem quickly and that it isn't too serious. Sorry I haven't got any immediate suggestions on identifying / solving the problem. With a bit of luck the compression test will give you a good idea of where to look further ...then it will probably be a head off job unless you know someone with an endoscope - not something many of us have an our toolboxes unfortunately. Let us know how you get on.
Paul

[P3Steve]

Well I think I’ve had a lucky escape. Took the head off fearing the worst, straight away though I could see it was No. 5 piston as there were a couple of bits of chewed up metal laying there and a few marks on the piston crown but all the valves were intact. At first I couldn’t figure out where the metal bit had come from but then having a good look around the inlet manifold it soon became clear. Inside what the parts and work shop manual call the inlet manifold centre pot which is the main body under the carburettor is a dividing plate which sits on two small Dowels (part No.210662) these oscillate in two slots allowing the dividing plate a few mm of movement from side to side. One of the dowels had become dislodged and the slot it moved in had been gauged out so it could come free and travel down the manifold into one of the pistons. Although the bit of metal were a bit chewed up you could see from there size and shape that this is what it used to be thankfully because it was so small it had only marked the piston top not punched through and the engine its self seem in very good shape with no noticeable wear on the bores and turning over very smoothly, although the valves seem ok as I’ve got a spare set of exhaust valves I’m going to decoke it any way and replace them. Next question is how to fix the problem making a new dowel wont be enough as the slot that it sits in has opened up and it would just break free like the old one so possible solutions 1) a replacement manifold – any got one? Or 2) drill out and tap the bottom of the manifold and make screw in dowels but this would stop the plate from moving as much (what effect would this have do you think. the original idea was to allow for air press equalization I guess) so working to the idea that the car is only driven gently would this make much difference to fuel and performance after all the plate is quite a “loose” fit with a gap under it so there must be a certain amount of air/fuel that can get by - what do you think? I would really value your thoughts on this. The main thing is the engine its self seems in fine shape. Steve ps although it means dropping the carb off it might be worth any P3 owners out there having a look as caught in time might save an engine strip!

[lakesrally]

Glad to hear the damage is limited Steve. I know nothing about this dowel and moving plate but, as the carb spends more time off the car than on it, I'll have a close inspection next time the carb is off. I might have a spare manifold in my barn, next time I'm over there I'll check it out for you. Best of luck.

[Paul Gregory]

Glad to hear that you have managed to track down the problem and that it looks like it hasn't done any significant damage. I wasn't aware of this plate arrangement so I guess I'll have a look at mine when I next have the carb off.
Hope you manage to get it all back together quite quickly.
Paul

[lakesrally]

Hi Steve, managed to visit my barn today, I have a complete cylinder head with manifolds and water pump so I could help you out if you still need a manifold. The plate you are talkng about is there but I cannot detect any movement at all.

[GOY189]

I would need to confirm, but as far as I know there is a 75 inlet manifold in the club stores.

Mike

[P3Steve]

I’m beginning to wonder if the “flap” was added as a late modification for production cars with out having to redesign the whole manifold after they found that having the manifold open under the carb was causing a swirling turbulence of the air fuel mixture a bit like having both car windows open on either side of the car at the same time – one side give you a nice air flow but opening both can cause quite a buffeting of air around your head so I wonder knowing the P3 was a “stop gap” car it wasn’t worth redesigning a new manifold at such a late stage of development so a quick “bodge” was used to get round the problem. I might have a go at fixing mine first where as the original dowels sat in holes in the base of the manifold and the dividing flap sits in slots in these dowels I was thinking of drilling and tapping two holes where the dowels sit and screwing some new longer dowels into these threaded holes so the flap cant move and the dowels can never break free (Two short pieces of threaded rod with slots in one end would be all that was needed) Let me give it a try if it doesn’t work I might need to take you up on one of the manifolds on offer but let me try this possible cheap but hopefully strong fix first.

[P3Steve]

Hi all i've only just had a chance to look at the Rover as I've been workinh away then my wife broke her leg so have been a bit busy but as I was cleaning up the manifold where the dowels sat my screw driver went right through into the water way below meaning the manifold is only good for scrap the metal being worn so waffer thin that it had almost worn right through so haqs any one got a P3 inlet manifold? let me know please. Regards Steve

[neil.henderson]

Hi P3steve,
Sorry to hear about your wife's leg - my wife just had to have a replacement of her hip replacement - because the 1st one started to leak cobalt - not good for you...............
Anyway, I have a spare inlet manifold on my spare engine (uses a Solex carb), but do you want to pay for postage from Australia? Just let me know....
Regards Neil Henderson