Valve Clearance problem

[Bobboloo]

Well I'm stumped.

I'm rebuilding a stock 2.4T. I've set the camshaft timing at 2.6mm lift at overlap TDC per the recommended amount. Problem is I only have a minimum clearance of .25mm at the point where the piston and intake valve are closest.

I've already shimmed the deck height up to 2.05 mm with 1.75mm worth of copper shims (1+.5+.25) which is already excessive.

What gives?

The P+C's are stock. Yes they are installed with the intake valve pocket up. Stock crank and rods. I verified the cam as a T cam. (measured it's lift with the dial gauge)

[Tim Walsh]

What about case resizing or head's being shaved?

[camgrinder]

What casting number are the cams?

[Bobboloo]

Well I think I've found the problem.

I checked clearance on cyl. 4 and got at least 2.5mm clearance so I knew something is not right on cyl. 1 so I turned the crank 180 deg from Z1 so I could verify that the valve adjustment screw is working properly on number 1. Same thing happened. I could only screw in the valve adjustment screw .25mm with the piston at BDC.

I guess this makes a good arguement for using solder or modeling clay to check clearance.

Time to tear the motor down and take out the 1mm shims and start over.

Tim, heads were not shaved. Case had spigots resurfaced but I initially added a .25mm shim on top the .5mm that was previously there. Then I added 1mm when I ran into this problem.

Cams are 901.105.133 and 901.105.134 but I measured the lift incase they might have been reground in a previous life.

[camgrinder]

measure the nose to heel of the cam and check that against the factory spec of 36.25 int / 35.51 exh. If they were reground in the past this number will be smaller of course. Grinding the "e" profile on "t" cams is very popular. Even with E cams you should have clearance.

John

[john walker's workshop]

so set them at the lower end of the spec. 2.40mm. if you shim out the cylinders/heads/cam towers, the cam thrust plate won't center in the chain housing.

[Bobboloo]

I pulled the rocker arms and sure enough the adjustment screw stops about half way. It must be slightly bent. Ditto for the exhaust rocker arm on # 1.

I have between 2.5mm to 3mm clearance on #4.

I'll replace the rockers on #1 tomorrow and check clearance.

[Wayne 962]

Good info - I didn't think to mention this in the book...

-Wayne

[NevenM]

Bobby

Thanks for the microswitch!

guess this makes a good arguement for using solder or modeling clay to check clearance.

I don't think this would work for a 911, 'cause by the time you had set the timimg the solder/clay may have been squished inacccurately

What I've done is asssemble heads 1 and 4 with only the inner valve spring, To check clearances you then just use the z-block and DG. With only one spring in you can press the valve down by hand, it saves all this pissing around with the adjuster screws and you cannot do any damage

Neven

[Bobboloo]

No problem Neven. Hope it works well for you. Your technique for checking clearance sounds good. I was hoping that I would put the motor together, verify the clearance and move on but it didn't turn out that way. The short cut turned into a longcut.

As for the rocker arms it turns out that just about all of the rocker screws do not turn past a certain point which makes them un-useful as a means of checking clearance. It wasn't a bent screw but it seems that the threads aren't tapped all the way through on most of the arms. Really all you need is one that you can move around to measure intake and exhaust on #1 and #4.

[NevenM]

Bobby

Yeah the pre-assemble thing, The advice I got from my mentor/machinist was pre-assemble the whole engine, which I have done and it worked out well, its not onorous as you can leave out a whole lot (oil pump, all conrods and pistons except for
1 & 4) Then do all your checking. The theory is that one this is done you just pull the thing apart and bolt/glue it together in
complete confidence (Thats the theory)

Neven

[Grady Clay]

Bobby,

What is the history of the engine?
Did you have it running prior to disassembly?
What changes were made prior to reassembly?
Are you sure of your cam timing measurements?
Are the pistons in right side up?

Give us more info and perhaps we can spot the problem.

Best,
Grady

[Doug Zielke]

After Walt Watson told me how to do it correctly, I used solder to check the piston/valve clearances. It worked well. I did not like the method of screwing the adjusters in, for the reasons mentioned by Bobby.

[Wayne 962]

Originally posted by Bobboloo
No problem Neven. Hope it works well for you. Your technique for checking clearance sounds good. I was hoping that I would put the motor together, verify the clearance and move on but it didn't turn out that way. The short cut turned into a longcut.

As for the rocker arms it turns out that just about all of the rocker screws do not turn past a certain point which makes them un-useful as a means of checking clearance. It wasn't a bent screw but it seems that the threads aren't tapped all the way through on most of the arms. Really all you need is one that you can move around to measure intake and exhaust on #1 and #4.

Wait a sec - I think you guys have got it all wrong. For the piston clearance check, you only need to make sure that you have 1.5mm on the intake and 2.0 on the exhaust. This means that you only have to turn the rocker arm screws 1.5 turns for the intake and 2.0 turns for the exhaust, after properly adjusting the valves. There should be no issues with the rocker arms bottoming out, as all of the rockers should be able to turn in at least two turns.

A shortcut for doing this check is to turn the intake screw 1.5 turns and the exhaust screw 2 turns, and then rotate the engine to see if the pistons and valves touch. This is mentioned on page 174 of the Engine Rebuild Book. This method is more risky though, as if you're not careful, you may damage your valves.

-Wayne

[NevenM]

Wait a sec - I think you guys have got it all wrong.

Wayne,

I think you should read my post again, What I've done is pre-assemble the engine with the inner spring in 1 & 4, I then have set the clearance to 0.1 mm and set the valve timing. I can now measure the V to P clearance without altering the clearance (I just press down on the valve with a dial gauge setup). The reason I'm doing this and not just a simple 'check' is that I'm trying to raise the comp on my 2.4E as high as poss (I'm aiming for 9 to 1). In my opion you are more likely to damage valves by screwing in the rocker arm screws than you are by hand!

What I have found is that despite all the 'theory' when you are rebuilding a 31 yo engine you treat it as a totally new experiance and assume nothing.

What Bobby has experianced can be totally explained by ground cams and refaced rocker arms

Neven

[Grady Clay]

Neven,

Go look at the thread “Measuring deck height” on this forum and twin plugging question

Getting close without touching takes very careful work, particularly going from 8.0:1 to 9.0:1 with stock pistons. Been there, done that. Feel free to e-mail me or call.

Best,
Grady

gradyclay@hotmail.com
303-756-7308

[Wayne 962]

Originally posted by NevenM
Wayne,

I think you should read my post again - The reason I'm doing this and not just a simple 'check' is that I'm trying to raise the comp on my 2.4E as high as poss (I'm aiming for 9 to 1). In my opion you are more likely to damage valves by screwing in the rocker arm screws than you are by hand!

Neven

Okay, so everyone is a little confused here. What you are doing is not *checking* the piston to valve clearance (as the original poster was doing), but instead creating a *map* of the piston to valve clearance, similar to Figure 82 on page 172 of the Engine Rebuild Book. Then yes, your method would work well, but is way overkill for the 99% of people who are simply performing the standard clearance check.

-Wayne

[Bobboloo]

Hi guys, I just got back in town and noticed the activity on the thread.

I just wanted to recap a few things to help clear things up.

First off, the motor is a stock 2.4T. A bottom end rebuild was required because the motor had low compression due to worn out P+C's. It ran fine as it had recently had a top end rebuild but it showed bad compression numbers.

After measuring a deck height of .33mm with no shims I added .25mm shims on top of .50 shims to give me a deck height of 1.08mm.

The problem I encountered was on cylinder #1 when after setting valve lash I was only able to turn the valve adjustment screw an additional 1/4 turn or .25mm if you will after setting cam timing. I assumed that I only had .25mm clearance so I added 1mm shims on top the .25mm and .50mm shims. When I reassembled I once again could only turn the screw an additional 1/4 turn which stumped me.

(My problem should have been obvious at that point but I posted this thread and shortly thereafter it occured to me what might be happening)

The problem has now been rectified and clearances are good using just the .50mm shims that were originally on the motor. My deck height is now .83mm which is a little lower than I believe most would recommend but since I have atleast 1.5mm clearance now for exhaust and intake I feel that is adequate. Since the pistons are stock 2.4T pistons (7.0:1) I feel keeping the deck height as low as possible is a good thing.

I'll let you guys know how things go when I finish assembly and start the motor up.

As they say, there's more than one way to skin a cat. Each of the methods for checking clearance have their validity as far as I'm concerned. I just think that the lesson here is that if you choose to use the valve adjustment screw to check clearance you need to first verify that it can be used for that purpose by atleast making sure that you have atleast 2mm of extra adjustment. This can be done by turning the crank to BDC for #1 after setting valve lash and then seeing if you have at least 2 extra turns available in your adjustment screw. Then reset, check lash and go from there.

[NevenM]

Bobby

Did you CC the heads and dome vol?

Neven

[Bobboloo]

Neven,

I didn't CC the heads. In all honesty, I just want to get the motor in the car so I can sell it and devote my time to my 71'S. I didn't go for any mods to speak of for the motor since I'm selling the car and the next owner can do what ever they want. After this car is out of the way I'll be building a 2.7 or 2.8 RS motor for my 71'S.