4G32 cam in 4G30 - no inlet valve clearance

[75GC]

Is the stock 4G32 cam different than 4G30? I think the answer is yes based on the different engine timing specifications in my Gregory's manual. Here's why I want to try it in my 4G30:
1. Current 4G30 has lumpy/unknown cam
2. Dyno/carby specialist measured very low inlet manifold pressure -7mmHg (vacuum) rather than expected stock engine about -15mmHg, or at least -11mmHg for a lumpy cam
3. All 4 cylinders compression about 95-100psi compared with stock 149psi, despite previous owner installing "flat top pistons, heavy duty springs for 10.5:1 compression ratio"
4. Dyno/carby specialist suggested trying original cam and check valve clearances.
5. I have a spare 4G32 engine in need of an overhaul, so have (I think..) a stock 4G32 cam ready to try!

If I do try the original cam I'll have to reset engine timing as it's currently about 15 deg BTDC compared with stock about 6deg BTDC. Any other concerns you would have given this engine history?

[davetrees]

Note that there a couple of different "stock" 4G32 cams - identifiable by the number stamped on the rear end face of the cam.

"1"= the stock cam in the early (GB/A53) 4G32, and also the 4G31 and 4G33. Total lobe height = 36.363mm intake / 36.412mm exhaust
"6" = the stock cam in the later (certainly GD, not sure about GC ?) 4G32. Total lobe height = 36.517mm intake / 36.569mm exhaust

The "6" has slightly more lift than the "1" - quite similar to the early Galant GS cam (2) actually. The "6" is also the stock cam in the Lancer 1600GSR.

The stock 4G30 cam, according to the factory workshop manual, is a "0". Total lobe height = 36.151mm intake / 36.203mm exhaust

The various cams have different valve timing too .... see below, from elsewhere on this forum :

0 36.151 36.203 18/50 48/20 = 4G30
1 36.363 36.412 20/48 51/17 = early 4G32, 4G33, 4G31
2 36.519 36.571 24/64 67/21 = 4G31 GS (twin carb)
3 ?? ?? 32/60 63/29 = 4G32 in SOHC GTO
4 36.519 36.571 46/74 77/43 = factory competition cam
5 36.777 36.829 46/74 77/43 = factory competition cam
6 36.517 36.569 24/64 67/21 = later 4G32 (those with the "wide head", I think? - as per 2nd gen Galant, LA Lancer)

[75GC]

Great, thanks for the details. My 4G32 is from a 1974 GB, but I'll check the cam number.

[75GC]

I pulled out the 4G32 GB cam and it's a number 1. So I plan to try this in my 4G30, even though it has different lift and timing. Will post how it goes! I plan to pull back the timing to 5 deg BTDC as per stock 4G32 spec (currently at 14 deg BTDC). Also I don't think my vacuum advance is working as I sucked on the vacuum pipe with distributor cap off and it barely moved. I guess it would normally have about 20 degrees of vacuum advance motion? I'll also check compression to see if it increases above the previous 100 psi.

[75GC]

Well, I managed to install the #1 4G32 cam into my modified 4G30 engine today, and all went well until I checked the valve clearance on #1 cylinder inlet valve. The exhaust valve clearance was ok, but even when the adjustment screw was fully removed the rocker arm was still compressing the inlet valve, perhaps only a very small amount. Two photos below. First one shows the inlet valve sitting on the rocker arm even with the adjustment screw removed. I'm concerned that this will mean the inlet valve is not fully closed so will never make any compression and blow high pressure into the inlet manifold.

When I inspected the reground cam from the 4G30 I noticed the non-lobe side appears to be almost flush with the rest of the cam, like it has been ground on this side. I know the engine has "heavy duty springs and new valves" but I don't know if they are stock length. Is it possible the cam was ground on the non-lobe side so that the rocker arm lifts higher than stock to accommodate the longer valve springs? That's the only thing that makes sense to me today but very open to other suggestions! I thought the only difference between the #0 and #1 cams would be the lobe height, thinking this was when the valves were open, rather than the non-lobe side?

I think my options now are:
1. Re-install the 4G30 cam and live with the valve overlap and low compression/vacuum at lower revs
2. Have the #1 4G32 cam ground on the non-lobe side so the rocker arm can lift high enough so the inlet valves close
3. Rebuild the head with stock springs/valves so the stock cam fits.
4. Any other suggestions?

Inlet valve clearance


4G30 cam; appears ground on the "non-lobe" side?


Thanks, Andrew

[tandanus]

Are you sure you put the rocker arms back in their right places?
T.

[75GC]

Hi, yes definitely sure of the rocker installation, I didn't change anything in the rocker arms/springs, all held together when I swapped the camshaft (and arrows pointing forward). I had another look today and it looks like to me the rocker arms on the inlet side have already been ground to allow clearance for the inlet valve springs. I presume the replacement "heavy duty springs" were longer than stock and the "solution" was to make extra clearance by grinding the space in the rocker arm. The replacement stock cam (#1) from 4G32 engine looks to have slightly more lift on the opposite side to the lobe, when means the rocker arm sits higher on the cam and presses very slightly down onto the valve spring. It must only be open a small fraction of a mm, but since I don't have any valve clearance I'm not confident to try and turn over the engine.

Guess I'm thinking of pulling off the rocker arms and maybe grinding them slightly more to give the extra clearance. I'm a little concerned about grinding moving parts that could cause future issues, but not sure I can be bothered taking the head off and replacing the inlet valves/springs... More fun!

[75GC]

Anyone else have concerns about grinding rocker arms further?

[77GDWAGON]

I had this problem many years ago after fitting custom stainless O/S valves to my 4g32. Was fine with a reground cam that I was using at the time when the machine shop installed the valves but when I went back to a stock no6 cam I had the same problem. So out came the grinder to give some clearance. Just take your time and not let the rocker arm heat up to much.

[geezer101]

Me personally - I wouldn't do it. I'd be trying to do what you're already doing and work out what is causing the valve clearance issue in the first place. Have you looked at the rocker assemblies in a 4G32 to see if there is a physical difference between the 2? The rocker rails might sit higher in the cam bed which would change all the angles and clearances (and it would allow for a meatier cam)...hmm, this is a tricky one

[davetrees]

... or just go back to stock valve springs. There's no advantage in running HD springs unless you are going to be running 6000+ rpm regularly, and with a stock cam profile you won't be.

In any case, uprated springs if selected properly, shouldn't be any longer than stock ones - just stiffer ?

I reckon you have some other problem ...... have you checked whether the valve stems are stock length or not ? Is the problem only on #1 inlet valve, or all 4 ? You don't say in the original post.

[75GC]

Thanks, all good suggestions/comments.
I will check whether there's a difference between the rocker assembly 32 vs 30. Also I have only checked cylinder 1 clearance, so will go through all of them to check. All the inlet rocker arms appear to have been ground.
Yeah I think the engine was intended to be very high revving, but really doesn't work for my street cruising. In fact it really doesn't work well even when revving so that's one reason why I wanted the stock cam.
Appreciate the input as it's all new to me, but at least I'm learning and haven't broken it yet!

[geezer101]

IMO it won't be the new springs causing the issue. They can only expand as far as the retainers will let them. It has to be either the length of the valve stems, the rocker arms or the entire rocker assembly that is causing the issue...

[simon]

hi, is it using different spring retainers and/or colets?

[75GC]

Sorry, I'm not sure. I understand geezer's comment that the spring won't cause the valve to sit higher. Either the valve stem is longer, or something like the collets as you mention. Could it be the valve seat has been ground in the head causing the valve stem to sit higher? Either way, I have a clearance problem that either requires me to further grind the rocker arms or take the head off and fix it "properly". Although I will make sure all the inlet valves have the same issue.

[geezer101]

There should be a visible section of the tappet between the rocker and the valve stem tip (a couple of mm at least). For the valve head to be recessed that far into the combustion chamber it would've had the valve seats savagely cut back. I don't know about compatibility but how much difference is there between the cast iron rockers and the alloy ones in G32B belt drive engines? They might have a shallower contact face to the cam (although I'd be worried about how the alloy ones would handle the uprated valve springs).

[75GC]

All good thoughts. My current thought is to measure the valve spring length both with the rockers installed (contact with valve spring) and with them removed. I would think the difference would be approximately how much I would need to grind the rocker arms to allow the inlet valves to fully close. Either I'll take the rocker arms to an engine reconditioner to machine/grind, or I'll take the whole head off with cam/rockers intact and just ask for their opinion of what to do.

[75GC]

Update. Inlet valve spring length (fully closed, rockers removed) about 42mm. Stock 4G32 spring length 38mm. Clearly the valves in my 4G30 engine are longer than stock. Previous owner and engine builder tried to grind inlet rocker arms to provide adequate clearance, however it looks like the valve spring/retainer has still been contacting the rocker arm in several places, as shown by the arc indents in the rocker arm!

I measured the spring length with the rockers installed and removed, and I couldn't measure any difference in length. I think this means I only need a fraction of a mm additional clearance by grinding the rocker arms so I can then adjust the appropriate valve clearance using the adjusting screw. Let me know what you think of the rocker arm grinding, as I think there is ~ 3mm+ removed already...

4G32 stock inlet valve spring length approx 38mm


My 4G30 inlet valve spring length approx 42mm


Cylinder 1 inlet rocker arm showing previous owner's grinding to achieve clearance, but evidence that valve spring/retainer has been contacting rocker arm in several places. I think this means not enough clearance from grinding.

[75wagon]

I wonder if you can get valve spring retaining collets (or whatever you call them) that will lower the top of the valve spring.

In the 2 pics you have there, the retaining collets seem to be the only real difference.

Dave...

[75GC]

Interesting thought Dave, of which I have no idea..! Previous owner said valve springs were "shimmed for additional seat pressure", but that shouldn't change spring length. I agree, either the fully closed valve spring length needs to be shorter (new collets?) or more grinding of rocker arms, or head off and replace valves/springs.

[simon]

I agree with Dave, IF you can swap collets you might gain the clearance you need
simon

[geezer101]

There's an obvious difference between the collets and retainers in those pics. It almost looks like the collets aren't installed properly (but they must be or they would've shot out and into the rocker cover by now). And the collets on the offending valve looks damaged? I'd try this - get an original set of collet halfs and the valve retainer and swap it onto the problem valve. It should solve the issue unless the machined groove in the valve stem is higher up the stem towards the head. If that is the issue there's only one thing for it - remove the head and replace that valve. Annoying - yes. But that'll be the end of the drama and you can get down to finally driving it.

[davetrees]

According to the workshop manual, the installed height of the valve springs (inlet & exhaust) in a 4G32 is 37.3mm (38.3mm max)

Same for both the "stock" and "GS" springs. (Free length of the stock springs is 45.85mm, GS is 46.3mm .... GS springs have higher seat pressure, but the difference is in the spring tension, not the installed height !)

[75GC]

Yeah thanks, I read that in my Gregory's manual also. Maybe there is just something incorrect about the inlet valve installation or collets/retainer. Seems like a 38mm installed valve spring length would solve my problem.

[75GC]

Update. Decided to get some professional help with the head. Inlet valve seat pressure was only 15 lbs due to the longer installed length/height, so after trying a few options, ended up changing the inlet valves out from a Toyota (not sure what model), which matched the larger diameter head, but the collet grooves were ~ 3mm lower. This compressed the springs for ~ 50lbs closed seat pressure, and also gave the required clearance from the rocker arms. So now it's all bolted back together with new gaskets, stock cam and reconditioned carburettor. It idles much smoother (as expected) but needs a tune. So hopefully this will be the end of my engine mods for some time!

[geezer101]

Cool - I was wondering how this valve issue panned out.