Valve Clearance Criticality

#1
My SC Auto has been off the road for 2 years. The engine has been professionally rebuilt by a shop that specialises in older equipment.
I've probabably done 2 - 3 hundred miles since she's been back on the road & I've been chasing a problem with rough idle and poor bottom end performance. Not all bad, she cruises beautifully and runs at 81 degrees C
I still have some carb work to do as she is running very rich.

I checked the valve clearance (dead cold) and came up with the following:

No 1 Inlet 0.005" , Exhaust 0.010"
No 2 Inlet 0.005", Exhaust 0.011"
No 3 Inlet 0.005' , Exhaust 0.012"
No 4 Inlet 0.007", Exhaust 0.009"
Compression test shows a consisitent 150PSI across all pots.
Will these tight clearances contribute to the rough idle/poor bottom end?
 

Demetris

Well-Known Member
#2
In my experience yes, the valve clearances are important. With these being so tight i wouldn't expect it to idle nicely. Moreover you are asking for trouble when you run the exhaust valves tight in these engines, because they are prone to burn anyway. Try to have them at the middle of their range. It will be noisier, but it will run much more happier.
 
#3
Thanks Demetris, so that would be 0.009" intake and 0.014" exhaust.
The manual suggests you can take one cap off at a time and use spacers to keep the head in place. Does this tend to work if done carefully?
 

harveyp6

Well-Known Member
#4
I agree with all that Demetris has said, and would add that those clearances won't have closed up from what they should be to what they are in a few hundred miles so it doesn't say anything good about the shop that rebuilt it, especially seeing as there is a nice little plate with the clearances on screwed to the cam cover.

You can use spacers to reset the clearances without removing the head, but you need to be very careful about the order you slacken the caps off.
 
#5
Thanks Harvey, I think I will do them myself to ensure they are done correctly. I will lean on the shop to make up the spacers and sort out the shims but will do all the work myself.
Do you know what the diameter of the head stud is. If I can find this out I can measure the required length/s without disturbing the head.
Would appreciate any advice regarding the order
I won't know the shim combination they have used until I get the cam and cups off but is it as simple as removing thickness to open the gap up (i.e. reducing the inlet shim thickness by 0.004" on 1 through 3?
 

Demetris

Well-Known Member
#7
I have adjusted the valve clearances a few times myself without removing the head, following the procedure described in the factory manual, and have never had any problems. But yes, i took my time and was very careful, double checking with the manual every time (dim short term memory doesn't help...). The original head and gasket have never been removed from this engine, 110 K miles later.

Following Harvey's comment on the need to reset the clearances on a newly rebuilt engine, i have also bought this engine freshly rebuilt from an abandoned project, actually not even properly run in, and the valve clearances were also tight. I wonder if there is something that upsets the clearances during the first run of a new / rebuilt engine, hence the need to be addressed soon later.
 

Demetris

Well-Known Member
#8
Regarding the cam timing, you just lock the crankshaft and camshaft so that you don't disturb the timing with the cam removal. If you have the factory manual, the detailed procedure is there.
 

harveyp6

Well-Known Member
#9
i have also bought this engine freshly rebuilt from an abandoned project, actually not even properly run in, and the valve clearances were also tight. I wonder if there is something that upsets the clearances during the first run of a new / rebuilt engine, hence the need to be addressed soon later.
I've never experienced that. They may be difficult to set initially, but in my experience making the effort to set them correctly means that they stay set for a long while afterards.
 

Dave3066

Well-Known Member
#10
I've also reset valve clearances on my 2000 several times without removing the head. Ideally you need to know the sizes of the shims fitted as well as the current clearances to work out what size shims you need to correct the clearances. It's a pretty straightforward job and can be done in half a day if you have the right size shims. Shims come in specific sizes so it's not always a straightforward case of opening up the clearance by a given figure. You may have to compromise by 1 or 2 thou to get them all in.
 

Demetris

Well-Known Member
#11
I've never experienced that. They may be difficult to set initially, but in my experience making the effort to set them correctly means that they stay set for a long while afterards.
A coincidence then. To be fair, i could not think of anything that would "give" in the first run and close up the clearances, but i thought i 'd better ask just in case i am missing something.
 
#12
Thanks for all the advice. Does anyone have an old head stud they could measure up (or know the shaft diameter off hand) so I can make up a set of spacers?
 

harveyp6

Well-Known Member
#13
Does anyone have an old head stud they could measure up (or know the shaft diameter off hand) so I can make up a set of spacers?
They're bolts, I have some somewhere. They have a shoulder on the top under the head IIRC so I'll try to find and measure one tomorrow. The OD can't be too big either otherwise it fouls the dowel.
 
#15
I believe 2 m14 nuts are the same depth as the shoulder so can be used as spacers.
I took a head bolt into the hardware store and bought some oversized nut to use a spacers.

While you are there buy a few grade 8 washers for the head bolts. The original washers get a little mushroomy sometimes, and many need replacing.
 
#16
I guess taking one of the middle bolts out to measure and then reinstalling it (slightly under tensioned) is low risk, in terms of damaging the head and/or gasket
 
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