Valve to piston clearance
Discussion
So whats the correct method in checking and how much do i need?
I am concerned ive ran too close with recent head work.
I am using similar thickness gaskets ie MLS 50 thou (was Elring composites).
I made some weak springs from wire and fitted the heads and rocker gear. The inlet is touching the piston just off TDC. I only get clearance by double shimming the rocker gear. But there is no preload taken into account in the hydraulic lifter due to the weak spring.
A little confused and a little worried.
Help
I am concerned ive ran too close with recent head work.
I am using similar thickness gaskets ie MLS 50 thou (was Elring composites).
I made some weak springs from wire and fitted the heads and rocker gear. The inlet is touching the piston just off TDC. I only get clearance by double shimming the rocker gear. But there is no preload taken into account in the hydraulic lifter due to the weak spring.
A little confused and a little worried.
Help
Pupp said:
Noticed last night from some pics you posted in a thread over the last day or two that no cut-outs apparent on your pistons; maybe an obvious way out if you have gone too close? However, I'm actually wondering if it's more a cam timing issue - not normally the inlets that clout the pistons but the exhausts (open toward a rising piston) - I'd make sure the cam timing is not over-advanced
Thats interesting but wouldnt the exhaust have more clearance anyway due to the smaller diameter.I should add that the timing was set a while ago by one of our friends on here. The engine idled nice enough and peak power was at 6000 rpm. Its a Real Steel Typhoon.
Maybe i will have to pull get the dial gauge and timing wheel out
Pupp said:
Was assuming you'd had the cam out or timing gear off - scrub that if you've not disturbed anything there. Not familiar with the typhoon, what's the lift and duration etc?
From Real steel web page, @0,50" In .218, Ex .218, Lift In 0.48" Ex 0,48"From other source duration is quoted at 276
macdeb said:
Hi Mate, you need to check clearance with cam timed and lifter full of oil [lifters need to be empty when doing pre-load], plasticine on piston, bolt head, rocker etc, turn through cycle, head off and measure thickness of plasticine. From memory went for 30 thou' clearance but will check on that in my notes.
First thing i will do when i get home Thursday!OleVix said:
I think its strange that you have been able to run that cam without valve cutouts in the pistons! Might be very close indeed! I was told by v8d that to run the stealth I needed the valve reliefs!
The engine was built many moons ago and it was deemed the Typhoon was the biggest cam it would accept before the need for cutouts.I may have run into a problem with recent head work.
Block is a 4.6 crossbolted (ex range rover i believe). Was tophatted just over a year ago.
Pistons are shallow bowl 4.0 no cutouts and sit 1mm below deck height.
Heads are ex '500' with the big valves. Just been rebuilt by Dave Knight.
Used to run standard Elring composites, this check is with a 50 thou MLS fitted.
Cam is Real steel Typhoon.
Rockers were shimmed by myself last time i put it together. I checked and double checked the preloads and had to use slightly different shims on 1 bank.
Note Dave Knight said he had to take 5 thou more off 1 head to match the chamber volumes now measured at 28.5 cc (The chambers are relieved of the bump).
Pistons are shallow bowl 4.0 no cutouts and sit 1mm below deck height.
Heads are ex '500' with the big valves. Just been rebuilt by Dave Knight.
Used to run standard Elring composites, this check is with a 50 thou MLS fitted.
Cam is Real steel Typhoon.
Rockers were shimmed by myself last time i put it together. I checked and double checked the preloads and had to use slightly different shims on 1 bank.
Note Dave Knight said he had to take 5 thou more off 1 head to match the chamber volumes now measured at 28.5 cc (The chambers are relieved of the bump).
phazed said:
Just as well you checked!
Cam timing correct?
If so then it's fly cut pistons.
Drop the dump, release the rods, number the pistons and send to Chesmans on the rods.
They can separate, balance and assemble.
Only constraint, (apart from cash) is time!
I think the timing is out a little but dont think that will clear it.Cam timing correct?
If so then it's fly cut pistons.
Drop the dump, release the rods, number the pistons and send to Chesmans on the rods.
They can separate, balance and assemble.
Only constraint, (apart from cash) is time!
I dont have time to send the pistons off.
ClassiChimi said:
You boys rock.
So won't the piston be weakened by cutting the groove out or is it negligible?
Will it effect the engines balance or will you be doing it to all the valves ?
Alun
I am still undecided on the course of action.So won't the piston be weakened by cutting the groove out or is it negligible?
Will it effect the engines balance or will you be doing it to all the valves ?
Alun
I know people have used this cutter to good effect but it does make me nervous.
All 16 cut outs would be done as identical as possible in order to keep balance.
My other options are to fit a set of 4.6 pistons with new rings. The CR would come down but would still be accpetable.
Ultra thick gaskets could make life easier but lead times mean i wouldnt have them in time.
Pupp said:
Changing the cam profile will necessitate a re-mapping as well as upping the workload considerably to physically dial it in etc. Unless the existing one is thought to be worn, I'd be inclined to leave well alone and at least have the baseline of a known tune to work from if you're intending to run hard from the off. Got to be the better approach to pull the slugs and have them done rather than try to cut them in-situ.
Not really familiar with any of the cams you list, are they more top-end focused than your existing one? Again, the exhaust clearances can get very close indeed with longer durations (don't ask me how I know)
In my case its the Inlets that are currently the worst for clearance. I guess it all comes down to specific cam profiles, valve sizes, set up etc. Not really familiar with any of the cams you list, are they more top-end focused than your existing one? Again, the exhaust clearances can get very close indeed with longer durations (don't ask me how I know)
Theses cams are higher lift and longer duration but still hydraulic. I have the heads to accept them and my CR will still be in the 10's despite the valve reliefs. I would check the tune through the megasquirt but as soon as its up and running would be making a visit to Dale Bladen for a full RR checkover.
If i do get a bigger cam banged in i will also use adjustable pushrods this time.
Pupp said:
It's actually more to do with which way pistons and valves are travelling relative to each other, an inlet kissing a piston will intrinsically be at less risk of damage than an exhaust... actually not uncommon on four and five valve race bike engines with pent-roof chambers for the inlet reliefs to be completely clean of deposits and even have witness marks from contact at high rpms when clearances are absorbed through inertial loads etc
I guess thats why more clearance is given to the exhausts then.Gassing Station | Chimaera | Top of Page | What's New | My Stuff