Engine build

[TimW]

Hi All
I have a MK2 2.5PI engine that has a recessed block but flat pistons.  I am sending it to the engine builder on Monday.  My question is can i have this block decked and do away with the recess in order to get the compression up to 10.25:1 (along with a head skim)?  If so would i then use a non-recessed head gasket?  

[GT6 M]

what you worried about Tim, going thru like  Mr Brucie  did,!!!!

just stick to a 9.8 or 10 max,  as it gets very fussy, when the hot weather is here,!!!!!

so unless you running a knock sensor, keep it doon a bit,

regards marcus

[TimW]

796 wrote:

what you worried about Tim, going thru like  Mr Brucie  did,!!!!

just stick to a 9.8 or 10 max,  as it gets very fussy, when the hot weather is here,!!!!!

so unless you running a knock sensor, keep it doon a bit,

regards marcus

Marcus
Should i keep the recess and not skim the block? or deck the block do away with the recess and take a little less off the head to keep it to 10:1

[Nick Moore]

It might be best to leave this until you've seen how far up the bore the pistons travel. If they're at deck height at TDC, any decking of the block would have to be accompanied by skimming the pistons.

Some people (eg the yellow tuning manual) recommend removing the fire rings, but others go to great lengths to keep them and have no problems. I'll face this decision in a few months as well...

[Scottie55]

339 wrote:

Hi All
I have a MK2 2.5PI engine that has a recessed block but flat pistons.  I am sending it to the engine builder on Monday.  My question is can i have this block decked and do away with the recess in order to get the compression up to 10.25:1 (along with a head skim)?  If so would i then use a non-recessed head gasket?  

Tim, I had exactly what you describe done to my spitfire 2.5 engine. Don't know what CR I'm left with though. I had to deck the block due to deep scroes on the surface and then had pistons skimmed. I'm not aware of any issues with this approach.

[TimW]

429 wrote:

Tim, I had exactly what you describe done to my spitfire 2.5 engine. Don't know what CR I'm left with though. I had to deck the block due to deep scroes on the surface and then had pistons skimmed. I'm not aware of any issues with this approach.

Thanks Roy

The only issue i can see is push rod length.  If i just have the head skimmed then i think i may get away with using the stock push rods but decking the block may leave the push rods a little long.  I don't want to change the push rods if poss.  Anyone know if i can get the 10:1 compression by just skimming the head?  I have read the GT Tuning manual, Vizard's Tuning standard triumphs over 1300cc and the Triumph competition preperation manual all of which cover the non-recessed blocks only.  

Anyone know of a publication that covers the recessed blocks?

[GT6 M]

Tim, im running 10.8.1 on a head skim,, only reason the comp is this high is because I had this head on a 300 deg cam, so needed the comp to make it work low doon,.
but its really too much for the cam i got noo,. 268 deg

as mentioned before, you going to have moer work to doo, if you skim thee block,
as you got to put it all together, then measure it all up, then dismantle again,. :-/ :-/
and then maybe ,skim a piston or two, then if ye doo, balance all pistons, :-/ :-/

just aim for a 9.8 1 ish max,.

out of intrest, what cam you going to be running,

and more to the point, are you increasing the CC,s  cos if you are, the this ALONE,
will increase the comp ratio

so if you get what you think,by just a head CC measure,.
then it will be too high,due to extra CC,s of engine

Marcus

[TimW]

796 wrote:

Tim, im running 10.8.1 on a head skim,, only reason the comp is this high is because I had this head on a 300 deg cam, so needed the comp to make it work low doon,.   So do you have a recessed block?
but its really too much for the cam i got noo,. 268 deg

as mentioned before, you going to have moer work to doo, if you skim thee block,
as you got to put it all together, then measure it all up, then dismantle again,. :-/ :-/
and then maybe ,skim a piston or two, then if ye doo, balance all pistons, :-/ :-/   I have no problems in having this done if removing the recess is the way to go

just aim for a 9.8 1 ish max,.

out of intrest, what cam you going to be running,   I am running a TR5 cam (270deg) but may change as time and funds permits

and more to the point, are you increasing the CC,s  cos if you are, the this ALONE,will increase the comp ratio I'm not increasing cc's because the block is in good condition and doesn't need a rebore.  


so if you get what you think,by just a head CC measure,.
then it will be too high,due to extra CC,s of engine

Marcus

I  just need to know if i should have the recess machined from the block or leave as is?

[JohnD]

bq,
Why are you so fixated with skimming the block top?
You can achieve the CR you want just by skimming the head face, unless you are very unlucky and have a head with a shifted core, so that skimming breaks through into the water jacket.   Even so, that only occurs with excessive skims.

Skimming the block face incurs some other problems.
  You need to drill out the top thread of the stud holes, else they will raise the face around them, making it impossible to maintain block/head sealing at any CR.
Unless you intend to deck the block properly, equalising the piston heights, it will exaggerate the inequality.

ST adopted the recess and the fire-ringed gasket for good reasons, to maintain a better seal.
I'd keep it and deal with the head.

Decking can be indicated.  I'm building an engine with a rather specialised head that I can't skim any more, even though the chambers are bigger than I would like and the resultant CR isn't as great as I would want.  I'll skim and deck the block and arrange the pistons to pop-up, to achieve the desired CR.

John

[GT6 M]

If it were me, then just skim the heed,

Marcus