Engine - Flutter or Misfiring [Now Valve Replacement]

[Monty-4]

Hi folks,

My 4-door 1098 saloon has been driving beautifully up until now. However while out on Sunday I experienced a quite sudden loss of power and what I thought felt like misfiring but after limping it home it seems to run well idle and revving while stationary.

I've checked the distributor cap, rotor arm, points gap, swapped condenser, verified spark on all plugs, no smoke from oil filler hole when running, no mayonnaise in filler cap & no oil in water, scoped timing looked right I think (~6° at lowish RPM, maybe 750).

I'm thinking something on the carb? Something sticking? Dirt in there somewhere? I've never touched a carb before other than adjusting the idle speed and fuel mix.

[bmcecosse]

Check the carb piston rises and falls nicely and add a few drops of engine oil to the dashpot.

[Monty-4]

Thanks bmc, I'll do that after work tonight!

[Monty-4]

Topped up/overflowed the dash pot, gave various bits a poke. Cleaned out a bit of grime from bit with the float and ran some cleaner through the carb. Played with the mixture a bit (it was a little lean, I think) and took the rocker cover off for an inspection and gapped the valves (all dead on 0.012). Drove it round the block and no improvement.

Took a quick video on my phone but I don't think it'll tell anyone anything: https://goo.gl/photos/xri9eLStDWeiXbkt5

Head off tomorrow or further carb investigation? I'm going well beyond my knowledge/experience here!

[bmcecosse]

It's going to be ignition then. Is the vacuum advance all connected and working? Suck the pipe and watch the baseplate move back and forth. Try a different condenser/rotor arm etc and check all connections.

[Monty-4]

Went through the ignition system again, no problems.

Then took the plunge and did a compression test. 160, 30, 160, 160. Uh oh. Head off...



Now I'm out of my depth.

[panky]

OOOOOO that's a nice one
If the seat hasn't been damaged it's just a case of changing the valve. Might as well strip the lot down while it's off and give the valves a good grinding.

[Monty-4]

Is it worth getting all new valves or just the one and grind the existing ones in?

[panky]

Strip it down first to check, no point in buying stuff you don't need. Post some pictures once it's in bits so we can have a look.

[bmcecosse]

You said 'fluttering' not blatant 'running on 3 cylinders' May as well bang in a set of new exhaust valves... This is why the 15 thou gap is important , with regular checking every 3000 miles.....

[Monty-4]

Haha, yes, perhaps I was too subtle in my description of the power loss. I'm new to all this!

Thanks guys. Should I run with 15-thou gaps even with additive?

[bmcecosse]

Forget the additive - it's a complete waste of money. MG / Rover went to 15 thou gaps when unleaded fuel became the norm. I see no reason to not follow that advice.

[Monty-4]

Cleaned up the head a bit, haven't done the valves themselves yet and they're very black and crusty, might just fit a full new set. The old head gasket was shiny grey and had a weird rubber layer to it that's left an imprint, possibly aluminium?

[bmcecosse]

The exhaust seats could do with a light re-cut, or you will be there for ever grinding in. Def get new exhaust valves. Are the guides worn? They look slightly oval in the pic, but maybe just camera effect.

[Monty-4]

I think the oval effect is just the camera. I don't have the equipment to re-cut or the budget or time to send it off - got to get to the national! Perhaps a lot of elbow grease and coarse grinding paste before the fine?

[bmcecosse]

There is a 'cheat' that may help. Cut a square of emery paper slightly larger than the seat - put a hole in the middle - fit the old valve over and push it in the guide. Grip the valve stem with a drill and give it a few light spins.... You may need to do it a few times - finishing with finer paper. Then get grinding! A spare cylinder head is always a good stand-by.......

[Monty-4]

Phew! Done but it did take a while. I did a very small amount very cautiously with the 'cheat', then coarse grinding paste, then fine paste, the cleaned up with a touch of oil and a clean rag. Will look at reassembling it all another night. I've been grinding/sanding any rust down and repainting everything I've taken out so it's turned into quite a big job that's taken over half the kitchen.

I think it'd be fun and worthwhile to restore the whole engine bay - if only I could get out of full-time work to do it as quick as I like!

[Monty-4]

Sorry for the double post but I'd just like to ask if there is anything I should bear in mind for reassembly as I've never done the head before. I'm aware of the following:

• Grease the thermostat cover bolts.
  Clean top of block - glass scraper and oil at hand.
  Clean bottom of head - ditto.
  Head on.
  Tighten bolts "in the right order", I imagine this is in the manual/Haynes.
  Attach everything else - manifold, heater tap, radiator.
  Tappet clearances to 15-thou.
  Rocker cover on, bolt down.
  Heat cycle.
  Tappet clearances to 15-thou.

Missed anything? This car has to get me to the national in two weeks and then move me to Scotland for a new job two weeks after that!

[bmcecosse]

Torque to 44ftlbf. Retorque after the first heat cycle. Just the ex valve gaps at 15, the inlets can safely be left at 12...they don't get as hot as the exhausts. Oh and copper gasket is best, and you may wish to consider ' top hat ' seals on the inlet guides if the car has a blue haze when starting away.

[Monty-4]

All appears to be well after a short trip around town. Thanks for your advice bmc & panky! 'Ol Monty is running again.



*yes I know, the lady won't let me take the peaks off*