head re-fitting problems

[mrmorrisminor]

Hi,
I've been working on a standard 1098 engine that blew its head gasket beteen 3 and 4. Previous to this all had been relativly ok the the exception of a slight misfire at tick over.

When we removed the head the top of the block was ok and there was a slight mark on the bottom of the head. Taking the valves out for a re-grind we saw that there was a cracked exhaust seat (which tied in with the misfire) so it was decided to go for an unleaded re-con head from a trusted supplier.

We have fitted all new studs and manifold gaskets as well as a new head gasket. All the surfaces were clean before refitting and the nuts were tightned in the correct order to the amount as per the manual. it's about the 20th time I've fitted a head on one of these so felt quite confident......... all was going very well.... or so I thought!

The engine will now only run on 3 cylinders, number 2 is a no go. the only action from this cylinder is a spit back through the carb when you try to rev the engine. So far we have tried/tested/changed-

-New HT leads
-New plugs
-clean/ reset the points
-There is a good spark on all cylinders!
-Static timing ( distrubutor was not touched anyway)
-Compression evident with the 'thumb' test (need to use a proper tester next)
-checked and re-checked the valve clearances

The only thing that I can see is that the inlet valve spring on number 2 is much softer to push than all the others, you can push quite easily with 1 thumb where as you need 2 hands for all the others. Could this be the cause? My thoughts are that if it is slower to shut then this could possibly explain the spit back as the ignition happens when it is still slightly open??

Any thoughts gratfully recieved, this one has me beat!

[ISELLHH]

Sounds like you on the right track. For the cost of Valve spring I personaly would change it.

[mrmorrisminor]

I have some spares from another head....... would be worth a swap I suppose to rule it out. I have been told it is quite possible to change a spring in situ... not tried it yet though

[chrisryder]

possible i guess. so long as the right piston is at tdc. only trouble is how to safely compress and release the spring without firing it miles into the air!

[mrmorrisminor]

I have had a little practise on a spare head on the workbench... If there are 2 of you, one to push the spring and one to remove the collet I recon it'll work....

Do you recon it could be the problem? I'm clutching at straws, been down all the usual avenues....

[chrisryder]

seems possible. can't imagine how anyone 'reconditioning' a head would miss a soft spring, but who knows?

i'd almost be tempted to try and change the spring in situ. if you drop a valve then you'll end up taking the head off anyway! nothing ventured nothing gained.

could be an idea to make a jig or frame or something to pick up on some of the head studs. gives you something to push against to compress the spring and release it gently.

it might not be so hard to get the soft spring off, but fitting a hard one might be difficult!

[mrmorrisminor]

A mate of mine who restored minis years ago recons you can do it with 2 screwdriviers

maybe we'll need a third person..... to watch where the spring flies!

As you say nothing ventured, nothing gained!

I bought a reconed engine a year or so back from a well-known place and it smoked like a pig.... turned out to be the rings fitted upside down.... so I'd rule NOTHING out!

[mike.perry]

For the sake of an hours work I would take the head off and have a final look down the bores and check every other part of what is now a suspect head. And no grovelling on the floor for lost collets which could escape down the push rod holes into the engine resulting in a complete strip down.

[Bazzalucas]

I changed all my valve stem seals a few years ago with the head on. Remove the spark plug and feed some soft rope into the cylinder. Compress the cylinder against the valves, then get to work above. I made a tool out of a piece of steel about 24 inches long with a 'hook' on one end and a piece of pipe a little smaller than the diameter of the spring. Drill a few 1/2 inch diameter holes in the pipe to access the collets with a needle nose pliers and/or magnet. Hook the hook around the rocker shafy, position the pipe over the spring, and lever it down. Remove the collets, and presto. Easier than it sounds.

[bmcecosse]

If one spring is 'soft' - what chance do the others have ?? And what faith can you have in the rest of the head - has it had new guides fitted - new valves - new oil seals - is it guaranteed to NOT be cracked or porous???? Has the head surface been ground flat?? Return the head and get your money back - you don't need an 'unleaded' head anyway!

[mrmorrisminor]

I can see it has had new seats on the exhausts and been skimmed. The head has been bought from one of our MAIN well known Morris suppliers and is billed as fully reconditioned.... I share your concern and it does not bode well for the quality of parts we are being sold.

All this aside.... Do you think a lazy spring would have this effect? My thoughts are that if it is slightly slow to close then it may be slightly open a the point of firing.

[bmcecosse]

You obviously are loath to name the MAIN supplier here - but if it's who i think it is - there have been problems reported before..... I would however think the compression would push the valve shut - are you sure the HT leads are on correct order - 1342 anticlock around the dizzy cap ?

[mrmorrisminor]

I'm confident on the order of the HT leads, all the other cylinders are firing, if you remove a lead at a time, the revs drop very noticably apart from number 2, this has no effect. As stated on the first post, we've changed plug, lead and dizzy cap. I'm going armed with a compression tester tomorrow, I,ve only used the thumb test so far.

The cylinder does eventually join in partly when the revs are raised quite high.... I suppose this could be when the compression is taking over... I'll report back tomorrow after another look.