I think my exhaust valves are burnt
 

Hello,
When I purchased my 30 Tudor it ran pretty good. It did have a little bit of a stumble during idle, but overall it ran well. I have put about 10,000 miles on it since then and it still runs well going down the road, but stumbles more than before during idle and you can hear it in the exhaust.

As far as I know the engine is completely stock, does not burn any oil and when i change the oil it still looks clean....I pulled the spark plugs and did a quick compression check about an hour after a long drive...so the engine was warm, but not hot. cyl #1-55psi cyl #2-63psi cyl #3-35psi cyl #4-65psi.

My gut feeling is a burnt exhaust valve on the #3 cylinder and the #1 cylinder may be suffering too. I see things on forums about marvel mystery oil working wonders, but I think that is on cars that have been sitting, this is a daily driver. I think it may be time to pull the head and inspect the valves, but I wanted to ask some expert opinions before just tearing into the engine.

What do you think?

Re: I think my exhaust valves are burnt
 

Pull the head and the side valve chamber plate and take a look. Not that hard of a job and then your going to know for sure.

Re: I think my exhaust valves are burnt
 

throw a little of the old red down it and see if it straightens out. then I would pull the side cover and roll it over and look to see if cyl 3 valves are coming down then take off the head and valve job/replacement. i gave my engine a new set of valves. set at .015 gap.

Re: I think my exhaust valves are burnt
 

Many Model A’ers regularly use MMO.....4oz per 10 gallons of gas.....

Re: I think my exhaust valves are burnt
 

I guess I will order some gaskets and prepare to pull the engine apart....but I do have a follow up question. I live in Southwest Michigan and I was wondering if there is anyplace that I could just take the car and have the service done...like I would in a modern car.
I know that when you own a model A you have to plan on fixing your own car, but I work full time and have a family so my free time is limited. I am not in a club so my only contact with other model A owners is through this forum.

Re: I think my exhaust valves are burnt
 

You could perform an abbreviated version of a leak down test.

Get #3 to TDC on the compression stroke, then with your air compressor and the proper fitting, charge that cylinder with compressed air...maybe 30-40 PSI.

Listen for where the air is leaking out (exhaust pipe, carb, oil filler tube) and look for bubbles in radiator. That should tell you what needs repair (exhaust valve, intake valve, rings, or head gasket).

Even if you are not in a club, you can contact one and there are probably folks there that would help.

Re: I think my exhaust valves are burnt
 

Before you get too carried away and start pulling the engine apart I think you should first pull the valve cover.Check the valve lash,if it has original lifters then you will have to pull the head to adjust the.If it has adjustables you can set without pulling the head and buying an expensive head gasket.Is there something going on that points you to,burnt,instead of,tight valve? I won't say burnt valves are a thing of the past,but they are a lot more rare than they used to be.In the 70's I used to see a lot of farm tractors burn the valves.Now I see the same tractors with loose and rattling valves,but not burnt.

Re: I think my exhaust valves are burnt
 

More gap or lash on the valves gives more time for the valves to remain on the seat . More time on the seat better cools the valves and reduces the risk of burnt valves .

Re: I think my exhaust valves are burnt
 

I read that Henry said with a little noise the engine will keep its poise .

Re: I think my exhaust valves are burnt
 

I would always suggest that pulling the head should be a last resort . The chance of wringing off a head stud in the block can be a big risk either when removing or replacing the head .

Re: I think my exhaust valves are burnt
 

[QUOTE= I won't say burnt valves are a thing of the past,but they are a lot more rare than they used to be.In the 70's I used to see a lot of farm tractors burn the valves.Now I see the same tractors with loose and rattling valves,but not burnt.[/QUOTE]


I agree that burnt valves are not very common today. I have a 31 Vickey that I bought several years ago. The engine in it had major work done on it back in the early 80's. All the exhaust valves are marginal and are not sealing at all well at all. The compression is down a bit and I can tell it is down on power but it still idles OK and runs good enough for around the town driving until I can find time to get all involved with rebuilding the engine and transmission.


I think running the valves extra loose will have little to no effect on the exhaust valves especially if they are already starting to burn. Once the exhaust valves start to deteriorate and do not contact the seat well, you have lost a most of the heat transfer from the valve to the seat.


Hard seats and better material in the valves will do wonders to longer exhaust valve life.


My opinion,


Chris W.

Re: I think my exhaust valves are burnt
 

I agree with Dick S. Do a diagnosis first. Obtain (or make from an old spark plug) an air fitting that will screw into the spark plug hole on #3 and hook up a compressor hose to it. Do the abbreviated leak down test. You will need a compressor, but a small one will work fine. Where you hear air escaping will tell you what's wrong. Carburetor = intake valve, exhaust pipe = exhaust valve, oil filler tube = rings or hole in piston, bubbles in radiator= head gasket. I would set the parking brake and chock a wheel in case the piston is not exactly at TDC.

Re: I think my exhaust valves are burnt
 

You should probably do a leak down test on another cylinder to compare air leak noises.

Re: I think my exhaust valves are burnt
 

squirt oil in #3 and repeat the compression test,if it comes up its rings,if it stays the same its valve. I you find an outside shop that will do the repair,look for two things..experience doing model a's and being capable of doing a correct diagnosis, start any repair with a shop with a 'diagnose and advise'..it helps avoid sticker shock,that unsettling phone call that starts with 'we found' after you authorized repair.

Re: I think my exhaust valves are burnt
 

After the symptoms appear and the valves are burnt, its too late for adjustment to solve the problem . I set my valves , intake and exhaust at sixteen thousands . Snyder's recommended this setting several years ago and it has worked well for me . I use this setting with original cams and my Winfield 3/4 race regrinds .

Re: I think my exhaust valves are burnt
 

Retrofitting modern valves and seats cure the burned valve issue through advancement in metallurgy.I run a 'C' grind cam (high lift B) with a .015 clearance based on this. Ford recommended a .022 clearance originally,to help cure the burn issue.Seat duration,as stated before,cools valves..if you run original ford valves pay heed.

Re: I think my exhaust valves are burnt
 

Are the plugs a consistent color? Is #3 very white or oily looking. A scope on a cell phone can give you a look at the valve head. Could just be a head gasket leak.

Re: I think my exhaust valves are burnt
 

My spark plugs all look good and are a consistent color. I guess my next step is a leak down test. My gut feeling is a leaking exhaust valve.

Re: I think my exhaust valves are burnt
 

The leak test is the best and easiest way to find out. Generally a burnt valve will show a compression reading of zero. If it is a valve then it is just starting to burn. It may just be sticking or not have enough lash,etc. If it is getting burned though it'll need to come out and be fixed. Its worth the time to find where the problem is before tearing to much stuff apart.

Re: I think my exhaust valves are burnt
 

MMO helps lube top end valve stems etc.ethonal gas very dry! U know that.!