25 replies to this topic

[Northernpower]

The problem using a ruler is it can only check along the length of it it can't compare that measurement with the for and aft measurement. The only way to do is with a surface plate and some fine wet and dry gently rubbed over the block face to identify low spots.

[Mito]

It appears that it has been blowing slightly between all cylinders. You can see carbon deposits on the bottom of the gasket between all of the cylinders and carbon deposits are on the block between the cylinders. There's also indications of heat between cylinders 2&3. Surely the block wouldn't be warped along the length of it? Wouldn't this be a an indication that either i've not tightened it down correctly (it was tightened to the torque specified in the haynes) or that something has held it off, resulting in it not being torqued down correctly?

 

I don't have access to a surface plate, so it's not really an option.

 

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Edited by Mito, 29 April 2017 - 10:33 AM.

[Mito]

The problem using a ruler is it can only check along the length of it it can't compare that measurement with the for and aft measurement. The only way to do is with a surface plate and some fine wet and dry gently rubbed over the block face to identify low spots.

would a sanding block do? What grade wet and dry should be used? And I assume it should be sanded dry?

[Mervyn]

Gosh that's running rich as a *******. Get it setup

Edited by Mervyn, 29 April 2017 - 01:00 PM.

[Northernpower]

The problem using a ruler is it can only check along the length of it it can't compare that measurement with the for and aft measurement. The only way to do is with a surface plate and some fine wet and dry gently rubbed over the block face to identify low spots.

would a sanding block do? What grade wet and dry should be used? And I assume it should be sanded dry?

A sanding block is no good; it'll deform under the pressure of your hand as you start to rub it over the block. You need something more substantial. Use 600 grade dry sanded, you're only rubbing it lightly over the block to highlight any low spots; you mustn't try to reface the block. You'll only get one go at it so don't apply too much pressure

[tiger99]

If in doubt strip it and get it very lightly surface ground. The steel rule check is not very effective. A very flat thing such as a sheet of plate glass and some engineer's blue might be more revealing., or it is possible to do flatness checks with a DTI. But all this needs the services of a properly equipped machine shop. Some things really can not be done reliably at home.

 

But before going to those drastic measures, have you taken out all the studs and very carefully used a countersink to deburr the holes, in case a raised burr is preventing the head from seating properly? It is one of the few simple things left to try.

 

The other thing is that it is, as said already, possibly running rich. Not sure that I am fully convinced, but given that it is out of sorts in either the fuel or timing departments, or both, has there been any detonation (pinking)? Unfortunately you can't hear high speed detonation, which may also have been happening. The reason I ask is that the peak pressures involved would do the engine no good at all, and could account for the head possibly being bowed across, not along, its width, given that both sides of the combustion chambers are clamped down by the studs but there is nothing on the centre line. Transverse bowing would certainly cause the gasket to be leaky down the centre, but would it be the head, or block, or both that was bent?

 

If you do decide to deburr the holes (carefully do the underside of the head too) and give it another go, with a known reputable gasket, I suggest torquing up in the correct sequence, 10 lb ft at a time, with oiled threads. Loosen the only nut you are doing slightly before bringing it up to its next multiple of 10, and continue till you get to the full torque. Give it a quick run up to temperature, immediately retorque (loosening the one nut very slightly each time) to the full torque, and of course readjust the valve clearances (you will be getting very good at that!). Run it on the road for a couple of hundred miles, and do the retorquing process again. If there are still problems soon after, it needs to go to the machine shop as there is nothing else useful that can be done.

[Mito]

I think I'll give that a try tomorrow. I don't think it was running that rich before it really blew and I did run it on choke to get it up the drive and then a bit more while diagnosing whether or not it was the head gasket, so may be this is why it looks like it was running mega rich. 

 

Since I don't want the car off the road for a long time and I haven't yet got the space for stripping an engine down and rebuilding it, I'll probably look at buying another running 998 and drop it in rather than take mine to an engineers. Actually, the local engineers has an a series 998 in their foyer. May be I'll ask them about buying it!  Then look at rebuilding this one when I have the space. A spare rebuilt engine has to be a handy thing to have waiting...

[Mito]

So, countersunk the holes as suggested and put it back together. Tappets are set up and I've just run it up to temperature and re-torqued the head.

Something looks very wrong going off of the spark plugs though...



1 & 4 don't appear to be firing???

[panky]

How about trying the fuse wire trick

 

Check this out at around 1 minute.

 

[Mito]

How about trying the fuse wire trick
 
Check this out at around 1 minute.
 

I considered that.

I've just got it running again though and going back to an earlier comment about it being too rich, it looks like the opposite was the case and it was running far too lean. I've richened it up a bit now and will check again after I've rechecked the valve clearances.

[tiger99]

Well done! If it was lean, that may indirectly account for all the problems.

 

Have fun!