Engine prep info as requested

[S_Gault]

As im finishing off a wee engine and I have recently read that a certain person has suggested swinging the cam timing using verniers on the rolling road, it struck me as to how dangerous this little bit of "advice" was.

heres the point- you swing the camshaft, it changes the valve to piston clearance by quite a margin.

So when I build an engine I measure the clearances (not just at TDC but also several degrees before and after (as valve acceleration is much faster than piston).

Then I know how far i can swing the timing before it becomes an issue.

First using a dial guage (with head off) get a good accurate TDC mark. I tend to mark this on flywheel tooth as its pretty accurate pointer... as in pic.

 

[S_Gault]

next assemble head with 2 dummy valve springs, and place on block, fit timing belt and set to marks. PLace a dial guage on the valve retainer and zero, then manually push down and check the vlave to piston clearance. turn engine slightly and repeat.. then repeat for exhaust valve.

All as below.

 

[S_Gault]

then move the cam timing one way then another till the clearance starts to get tight when you check it.

Then take your vernier pulley and mark on the scale the "NO GO" areas.

as below.

BUT and ITS a BIG BUT, you cant do this with a hydralic follower coz the clearance will be different once the engine starts!! I let you work that one out for yourself.

Steven

 

[S_Gault]

forgot the pic

 

[Adam]

Cool, so say in cars with hydraulic followers like my car, what would you do?

 

[Baz C]

u really know u stuff dude!

 

[Phil-Ray]

the amount of trouble u must go to do to this stuff is quite astounding

would most engine people do this amount of work?

 

[andy_gdon]

what can you do for my dirty derv??

 

[VEN©M]

Cool, so say in cars with hydraulic followers like my car, what would you do?

i'm also running HLA's, hopefully converting to solid shims with the new cams!

 

[RMS_CLK]

How come the engine in the picture has hydraulic followers, or is that just for demonsration purposes?

 

[S_Gault]

I have a way of doing it with a hydralic follower but I have to keep somethings a secret!! Taken me many years to come up with some ideas... cant give it all away in 5 mins flat..

engine in pic has hydralic followers but not in clylinder that im checking the clearance on.. something quite different.

ANd hydralic followers are no disadvantage.. only in a racer.

Steven

 

[VEN©M]

steven i was told that the HLA's in my car would rattle like a bitch if i went to aggressive on the cam profile as reducing the base circle too much on a re-ground standard cam was baaaad.

can u discuss more on this issue? my car is running HLA's and i was led to believe that solid shims would be a better approach for cams of duration 290' and more.

 

[Fast_CAV]

sr nova engine...

 

[Jason]

steven i was told that the HLA's in my car would rattle like a bitch if i went to aggressive on the cam profile as reducing the base circle too much on a re-ground standard cam was baaaad.

can u discuss more on this issue? my car is running HLA's and i was led to believe that solid shims would be a better approach for cams of duration 290' and more.

pete lad why wud u want such lumpy cams?? would be a bitch to start/idle/drive/fuel etc!

 

[Fast_CAV]

But will be fast!!!!!!!!!

 

[Jason]

he'll have to raise the limiter and do internal work to get the most of it.. prob jus blow up the engine!

 

[Fast_CAV]

Oh well Its all fun and games anyway...

 

[S_Gault]

why use big cams with a turbo engine? doesnt make sense.. all the boost goes out exhaust valve on overlap at TDC.

but to answer the question, yes decreasing the base circle is bad as you can run out of range of the hydralic follower adjustment, but it may not be soe bad if you look at whole pic- if you cut the seats in the head, the vlave moves up .. you get it back.

Steven

 

[RMS_CLK]

Thats not always a bad thing, as the scavenging mixture can work like anti-lag igniting in the manifold and keeping the exahaust turbine lit!

 

[S_Gault]

no, doesnt work like that... I wish it did, its not the mixture that causes scavenge its the pressure wave and I wrote a thesis on it when I was at Queens on a grand prix bike engine and its uses.

Steven

 

[RMS_CLK]

No i totally agree with you that wild cams are not what you want on roadgoing turbo engines, but I did also read that a bit of mixture escape on overlap can keep a turbo spoolling - never tried it myself.