Shaved heads and timing

[thmag99]

Hi guys,

Couldn't find an intro section here so i thought i'd get straight into it.

I have a 4g93 engine (yea i know its not toyota but i need info) and during my build i shaved the head by 1.5mm to scrape some compression.

I rebuilt the head with a stage 3 port and polish and a 1mm headgasket. I timed it all up to stock specs and fired it up.

It worked for about a day and a half but i had a wicked ticking noise which turned out to be the exhaust valves smashing the pistons. In turn my engine died and i had bent all 8 valves.

So i guess my question here is, must i find a new TDC? Or is it my cam timing that is out?

I have been told by numerous people that i need to find a new TDC using a piston stop and degree wheel?

I have thrown the head back on after rebuilding it again, this time im using the stock 1.3mm headgasket.

Any help would be appreciated!

[w810sc]

Your cam timing will most likely be out. Easy way to fix this problem is to get yourself some adjustable cam gears or sprockets for your intake and exhaust cam and if possible degree them.

How are you cams aligned in the standard spec? do you have arrows or notches that need to be in a specific position?

Also before you put your head back on I suggest you put some clay doe in the cylinder chamber and turn the motor by hand and find out just how close the valves are to the piston @ TDC.

My head and block are also shaved 0.010" each and I'm using a 0.8mm metal head gasket, adjustable cam gears are the way to go.

[Ben Wilson]

If it's anything like an EVO motor you probably stuffed up the timing belt tensioner. They are very easy to get wrong...

The numerous people are wrong - You haven't touched the bottom end so the TDC mark on the crank will be OK, you might have to fiddle with the cam timing a little to get them right (interestingly when I shaved heaps off a 4AG head the cam timing lined up perfectly).

[thmag99]

Your cam timing will most likely be out. Easy way to fix this problem is to get yourself some adjustable cam gears or sprockets for your intake and exhaust cam and if possible degree them.

How are you cams aligned in the standard spec? do you have arrows or notches that need to be in a specific position?

Also before you put your head back on I suggest you put some clay doe in the cylinder chamber and turn the motor by hand and find out just how close the valves are to the piston @ TDC.

My head and block are also shaved 0.010" each and I'm using a 0.8mm metal head gasket, adjustable cam gears are the way to go.

Hi,

Thanks for the info.

I have already got the head back on a torqued down.

Only one problem with the cams, i cant really afford an adjustable cam gear at the moment, my head config is also SOHC.

I've also been reading up about dialing in cams using a dial gauge indicator and degree wheel, will i be able to degree the cams to the correct config i need using this method?

Also, will using the stock headgasket (1.3mm) or the MLS Headgasket (1mm) make any difference to piston-valve clearance?

I very much appreciate the help

EDIT: The cam gear has a small arrow on one tooth, the head also has a small arrow, and these are currently lined up, all valves closed except cylinder #3 which has exhaust valves open 1/4 way

[thmag99]

If it's anything like an EVO motor you probably stuffed up the timing belt tensioner. They are very easy to get wrong...

The numerous people are wrong - You haven't touched the bottom end so the TDC mark on the crank will be OK, you might have to fiddle with the cam timing a little to get them right (interestingly when I shaved heaps off a 4AG head the cam timing lined up perfectly).

See this is what i don't get. "apparently" the timing marks for the cam on the 93 are pretty good from factory, we have gotten a 272 cam to work with stock timing marks. The only concern i'm really having is that TDC was way off when i timed it up, hence why it bashed my poor exhaust valves.

Could you elaborate on the tensioner issue for me?

[mullett]

are you using standard cams, or aftermarket? It could well be that you didn't check the timing markes after tensioning the belt (by rotating the engine a few times from the crank with a spanner) and it was a tooth out...

-RM.

[andrew_mx83]

Also, will using the stock headgasket (1.3mm) or the MLS Headgasket (1mm) make any difference to piston-valve clearance?

about .3mm???

[thmag99]

are you using standard cams, or aftermarket? It could well be that you didn't check the timing markes after tensioning the belt (by rotating the engine a few times from the crank with a spanner) and it was a tooth out...

-RM.

I am using standard cams, when i tensioned the belt it was a tooth advanced, but when i rotated the engine by hand twice, both TDC and cam marks were spot on. However this time, if i use stock timing i will be smashing valves again, which is what i dont want.

[w810sc]

Hi,

Thanks for the info.

I have already got the head back on a torqued down.

Only one problem with the cams, i cant really afford an adjustable cam gear at the moment, my head config is also SOHC.

I've also been reading up about dialing in cams using a dial gauge indicator and degree wheel, will i be able to degree the cams to the correct config i need using this method?

Also, will using the stock headgasket (1.3mm) or the MLS Headgasket (1mm) make any difference to piston-valve clearance?

I very much appreciate the help

EDIT: The cam gear has a small arrow on one tooth, the head also has a small arrow, and these are currently lined up, all valves closed except cylinder #3 which has exhaust valves open 1/4 way

Degreeing your cam should solve most of your problems, but you will need an adjustable cam gear to make the adjustments. From this you can find out:

- intake cam duration advertised and at 0.050"
- exhaust cam duration advertised and at 0.050"
- intake valve lifts
- exhaust valve lifts
- valve lifts at TDC
- LSA - Lobe separation angle (you need to do some simple calculation.)

piston to valve clearance will depend on your LSA, which you will notice when you measure in/ex valve lift @ TDC. Since your using a standard cam, you might notice a very small amount in performance compared to a higher duration cam in your hi compression motor.

The SOHC will have a set LSA, because both in/ex cam lobes are on the same cam. From factory they are ground to a certain spec. You will only be able to advance or retard the cam to a certain point.

You can try to increase the valve clearance to biggest allowable number to compensate too much valve lift.

I strongly suggest you measure just how much lift it takes for the in/ex valve to hit the piston @ TDC.
- Set motor to TDC
- place dial indicator stalk and compress it on the valve bucket/spring retainer so there is enough length of the stalk to measure the lift when the valve goes down.
- rotate cam slowly and and watch the dial indicator, as the cam hits the piston look at the dial indicator and record the result.

If this still doesn't solve your problem you will need to get a cam with the right specs to suit your motor in terms of lifts and duration.

[thmag99]

Hi,

Thanks for that thats some very useful information.

I will first try my boss's method then if that does not work, i guess its adjustable cam gear time.

[RAd28]

Don't want to hijack this thread, but i've been wondering about shaving heads myself, particularly on the 18RG... my biggest question is how much does a shave of something like 1.5mm translate into compression ratio increase? I know it depends on more then just the amount you shave off, but i'm just looking for rough estimates, or past experiences. Would 1.5mm get you a 10-20% increase in compression? or is 1-5% more realistic?

And is there any real difference between shaving the head or the block?

[andrew_mx83]

no difference for head or block.
rule of thumb is about 1 point of compression for 1mm (40thou)

[allencr]

So i guess my question here is, must i find a new TDC? Or is it my cam timing that is out?
I have been told by numerous people that i need to find a new TDC using a piston stop and degree wheel?

There isn't 'a new TDC', just verifying that the marks are accurate, what with manufacturing slop and a possible well known problem with shifting of a harmonic balancer's marks.

It's surprising that a stock cam piston setup with a few mm off of the head & gasket would have valve clash, interference engine or not. Maybe the head & block have been resurfaced before? What's a 4g93?
The retarded cam timing does put the exhaust valve closer to the piston that is chasing it up the bore during the exhaust stroke. Don't bother checking the intakes, they will still only be opening very little, while the piston is moving down away from them.

[LeeRoy]

What's a 4g93?

1.8L Mitsubishi engine, commonly found in lancers and galants amongst other vehicles.

[jimmmayyy]

4G's are interference engines, and there isn't alot of clearance even in a stock motor. Do the plasticine test first next time before you think of even cranking it.

The fact that your still using a standard cam and you still munched the valves should confirm that too much meat was taken off the head.