22 replies to this topic

[carbon]

So before i went carving into the head i thought i would do some more measuring just incase, and as Carbon said above i meaasured the exhust valve depths and inlet depths for that matter.

 

what i found is i measured the chambers wrong or read it wrong for one of them so this time the volumes were 18.6, 18.7, 19.7, 18.6 so all very close apart from one of the central chambers, the one closest to the thermostat. measuring the Exhaust valve depth in this one it is over 1mm deeper than the rest so as carbon said this would pretty much make up the 1cc difference in readings.

 

looking at the seat it doesnt look pitted or damaged it looks like it would when cut i think but its just a lot further into the head. all the seats look the same with the valves out and the other valve depth measurements were all very close to each other, max 0.2mm difference.

 

so my question now is what do i do with this one chamber being bigger, seems a bit mad to grind the other 3 out? or is this the way to go? i guess the only other option would be to install a whole new seat, anyone know the cost of doing that and a skim?

 

looking at the compression ratio i think this would give roughly 10.8:1 in three of the cylinder and 10.5:1 in the other, although i do need to check the deck height to check this. is that a big issue?

 

cheers

Unless you're seeking perfection I would use this as it stands for a road engine. May be worth trying all four exhaust valves in cylinder 2, as you may find one which does not recess quite as far.

 

Once the engine is run in I would recommend using a decent compression tester, and check if the reading on cylinder number 2 is measurably lower than the other three. With CR of 10.5 you should be getting about 200 - 215 psi

 

If you are seeking perfection you should also measure the distance from the top of the piston to the deck of the block, with the pistons at exact tdc. With a 21253 type piston the piston to deck clearance should be 7 thou. A 10 thou difference in  piston to deck clearance is 1.0cc.

[samboson]

Ok I found slark, do the others have businesses or contact on here?

Is it normal for one seat to recess, wouldn’t they all recess if unleaded was used on a leaded head?

Thanks

[samboson]

Thanks carbon I was thinking that. I’m going to take my head off the running engine next week and I’ll clean the pistons and check the deck height to be sure on the compression ratio. I think I’ll just put it on and see what happens and do a compression test. If it’s no good I’ll have it back off and get the bits done.

[mini13]

http://www.robwalkerengineering.co.uk/

Turbphil you can get on here that's his username

[samboson]

so i got it all together and made up the 1.5 rockers i fitted but have run into a problem. i cant set the rocker gap on rocker 4 and 8. on 4 it is nothing with the adjuster all the way out and on rocker 8 it is 0.2mm with the adjuster all the way out. i guess this is the issue with going with the recessed valves? i guess valvle 8 is also slightly recessed.

 

i will pressure test once finished tomorrow but i guess this will not be good? i.e. the exhaust valves are not going to close when the engine is warm and this will cause more degredation of the seats. i guess this is what happened to the head in the first place, the rocker was probably adjusted to tight on valve 4 and it burned the seat out.

[unburntfuelinthemorning]

Ideally then you need shorter pushrods but alternatively there's these:  http://www.minispare...|Back to search

[samboson]

yeah i cant seem to find shorter push rods? im sure i have read in the vizard book that there were shorter rods in certain engine builds but cant find them. thanks for the link to the spacers though, didnt realise they existed but guess it makes sense as so many heads are skimmed like the one im using. 

 

should be sorted for the time being. cheers

[unburntfuelinthemorning]

Pushrods can be shortened but I don't know who would do them properly.