Troubleshooting by exhaust temperature

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Troubleshooting by exhaust temperature

Postby kgroombr » Sun Dec 22, 2013 11:44 am

I am trying troubleshooting a 72 Vega engine I just rebuilt. I had a local shop do the valve job on it. It fires up OK, but it was running a bit rough. I checked spark, all cylinders getting good spark, but I noticed that when I pulled the wires off cylinders 1 and 4 that it didn't make much difference in the way the engine ran. When I pulled the wires off cylinders 2 and 3, there was big difference in the way the engine ran.

I used a temp gun and I found the exhaust on cylinder 1 running at about 200 degrees (essentially nothing), cylinders 2 and 3 at about 500 degrees, and cylinder 4 running at 800 degrees.

I am thinking that the shop that did the valve job messed something up. Maybe possible doing the valve job, and then mixing up the valves between cylinders 1 and 4. Any guess what what would cause such as variation in temps? The springs are original too, so could it be related to weak springs?

I googled a bit and found some information on exhaust temps and valve problems, but it didn't go into detail.

Thanks,
Ken
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Re: Troubleshooting by exhaust temperature

Postby vegrent » Sun Dec 22, 2013 12:04 pm

had that happen to me ...pull the two cold wires off cap side, lay them loosely on cap so they spark to wire.see if temp. comes up and run smoother.sounds crazy but give it a try...
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Re: Troubleshooting by exhaust temperature

Postby kgroombr » Sun Dec 22, 2013 12:15 pm

I will give that a shot. Assuming that helps, what would be the ultimate fix?

By you mentioning this, I should check to make sure I didn't swap wires 1 and 4.

Ken
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Re: Troubleshooting by exhaust temperature

Postby vegrent » Mon Dec 23, 2013 3:29 pm

bad wires , plugs fouled, my problem was a bad bad spark plug ...not sure about yours ,just trouble shooting for now... :wink:
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Re: Troubleshooting by exhaust temperature

Postby hammerdown7 » Mon Dec 23, 2013 4:44 pm

As I understand you are not using the stock plug wires because cyl 4 wire will not reach cyl 1. Possible the crimp on the plug wire is bad or loose. Swap plugs between 1 & 2 to see if the problem travels with the plug. Are you using a new distributor cap or is it a used one? If this doesn't solve the problem do a compression test, all cylinders should be within 10 psi of one another.

Dick
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Re: Troubleshooting by exhaust temperature

Postby kgroombr » Mon Dec 23, 2013 4:48 pm

Probably not going to help me. Brand new wires, and plugs (correctly gapped).

I am hoping it is as easy as swapping wires 1 and 4, but I am guessing that isn't it, since I put cylinder #1 at TDC, installed the distributor in accordingly, and wired starting with cylinder #1. I could see cylinders 2 and 3 mixed up as that would be going counterclockwise as opposed to clockwise, but I am only human and have screwed up some pretty easy tasks before. :)

Ken
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Re: Troubleshooting by exhaust temperature

Postby kgroombr » Mon Dec 23, 2013 4:52 pm

hammerdown7 wrote:As I understand you are not using the stock plug wires because cyl 4 wire will not reach cyl 1. Possible the crimp on the plug wire is bad or loose. Swap plugs between 1 & 2 to see if the problem travels with the plug. Are you using a new distributor cap or is it a used one? If this doesn't solve the problem do a compression test, all cylinders should be within 10 psi of one another.

Dick


Stock wires, but I could have had to swap them at the distributor for them to reach. Everything is new: rotor, cap, wires, points. Doing a restoration so trying to keep it original. I have an HEI distributor that I may toss in if I can't find anything.

A compression test would be the sure thing to tell me if there is a valve problem. I know the cylinders and rings are good as it is a newly sleeved engine with new pistons and rings.

Ken
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Re: Troubleshooting by exhaust temperature

Postby hammerdown7 » Mon Dec 23, 2013 4:54 pm

My mistake on the plug wires Ken, wasn't even thinking about a mix-up on the distributor! Guess I would try the compression test.

Dick
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Re: Troubleshooting by exhaust temperature

Postby vegrent » Mon Dec 23, 2013 4:59 pm

did you try the gap plug wire thing ?? did exhaust heat up??
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Re: Troubleshooting by exhaust temperature

Postby kgroombr » Sun Jan 05, 2014 5:39 pm

Just wanted to post the follow-up to this. Sorry it took so long but didn't work on the car through the holidays.

I did a compression test and #1 was nearly nothing and #4 wasn't much better. Before pulling the head, I took off the valve cover and checked the valve adjustment. #1 intake and #4 exhaust were tight. The adjusters were already as loose as they would go.

What really sucks is I purchased this head from a shop that rebuilt it years ago while I was up in the Washington DC area.

I have another head that is in good shape, and a new set of valves and springs, so will take them to a shop and let them know the minimum/maximum for the valve height. If they can't get it to fall within tolerance, then I guess it will be new valve seats.

Lesson learned. Will make sure to check measurements before accepting a head from a shop, or before installing it.

Ken
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Re: Troubleshooting by exhaust temperature

Postby rpoz-29 » Mon Jan 06, 2014 5:33 pm

I had a head years ago that had been sitting for a while. I took it to a shop for a valve job and the seats had to be cut. (apparently there was a little rust in the seats). When I got the head back, the valve stems were too tall to allow the lifters to be adjusted . They cut a little off the top of the valve stems, and it was good to go.
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Re: Troubleshooting by exhaust temperature

Postby kgroombr » Mon Jan 06, 2014 6:17 pm

rpoz-29 wrote:I had a head years ago that had been sitting for a while. I took it to a shop for a valve job and the seats had to be cut. (apparently there was a little rust in the seats). When I got the head back, the valve stems were too tall to allow the lifters to be adjusted . They cut a little off the top of the valve stems, and it was good to go.


I thought about having that done. If the other head doesn't pan out, then I may go that route. I wish I had a machine to do it myself. I hate trusting somebody else do do something right.

I think the head is in good shape, I just think the valves have been ground too much, so I sent to pull the valves out and the keeper area is binding up as soon as it hits the guide. I don't want to pull them out hard as I think it could damage the guide. Anybody know of a tool to trim down the edges of the keeper area? I think the lip expanded a bit causing the binding. I would use a file, but on the 140 head the keeper area is inside the tapper area so that is a no-go.

Thanks,
Ken
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Re: Troubleshooting by exhaust temperature

Postby kgroombr » Sun Jan 12, 2014 7:04 pm

I think I found one more option. In my shop manual it states:

NOTE: Tappet adjusting screws are available in three size ranges - standard and two undersizes

I see in the parts manual it lists the following:

5232770 screw tip plain .430/.451 - .375/.397
5232771 screw tip blue .438/.459 - .383/.405
5232772 screw tip copper .422/.443 - .383/405

Not sure how to read these to determine which one is standard and which two are the undersized. I would gues that 5232772 is the standard, and the others are the undersize, but it all depends on the reference. Also not sure why there are two starting and ending numbers.

Anybody know which one is which?

Thanks,
Ken
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Re: Troubleshooting by exhaust temperature

Postby MonzaRacer » Sun Apr 13, 2014 7:41 am

Well as an ASE master Machinist and very experienced head builder the previous shop didnt know crap about rebuilding heads obviously.
ANY competent head shop would KNOW that when you grind valves and seat you ONE) remove double the amount removed off valve face from stem, and TWO) You always check valve height before reassembly and also check and shim the springs to proper seat pressure. Heck the valve clearance (if on overhead cam heads)should have been set and locked down at cold settings at shop.
You dont replace seats unless the valve is recessed too far into the head, generally dropping in a new valve cures most issues.
I have seen so many SLOPPY, slap dash head rebuilds in my life. Sounds like you got one here.
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