Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
G
Guest
Guest
Guest
Offline
you have read this or similar right?
https://64.233.161.104/search?q=cache:yUh...&lr=lang_en
https://64.233.161.104/search?q=cache:yUh...&lr=lang_en
-
Hi Guest!
If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
There are some perks with a member upgrade!**Upgrade Now**
(PS: Subscribers don't see this gawd-aweful banner
A bad cam?
- Thread starter Morris
- Start date
Share this page
SilentUnicorn
Yoda
Offline
[ QUOTE ]
Very rapid movements. Roughly 9.5-11 in. Hg at idle and 14.8-17.7 in. Hg at highway cruise.
[/ QUOTE ]
I would have to suggest another look at your valve guides. i would be willing to bet they have loosend up, letting the valves chatter, rather than seat correctly. To do this you will need to pull the head and the valves, use a mic and a bore gage and see just what kind of tolerances you have on each valve to guide clearance. I only suggest this based on your previous troubles with guides. Your compression is ok. How is your timing chain?
mark
Very rapid movements. Roughly 9.5-11 in. Hg at idle and 14.8-17.7 in. Hg at highway cruise.
[/ QUOTE ]
I would have to suggest another look at your valve guides. i would be willing to bet they have loosend up, letting the valves chatter, rather than seat correctly. To do this you will need to pull the head and the valves, use a mic and a bore gage and see just what kind of tolerances you have on each valve to guide clearance. I only suggest this based on your previous troubles with guides. Your compression is ok. How is your timing chain?
mark
Offline
[ QUOTE ]
Problem: wildly fluctuating engine vaccum freaking out my ecu and causing poor performance.
Attempted solutions:
3) Removed and inspected head. Replaced two galled valves and guides. Checked valved clearances several times.
4) Compression check (front to back): 130; 130; 129; 140. This was pretty much the score before the problem arose. I believe #4 is getting a little extra oil resulting in a higher number.
So is it time to pull the cam? Could I have flatted my lobes with my sticking valves?
[/ QUOTE ]
The suggestion to check ALL of the cam lobes for uniform lift with a dial indicator is good.
Why did you only replace two valves & guides? The problem really sounds like you still have intermittent sticking/leaking valves.
D
Problem: wildly fluctuating engine vaccum freaking out my ecu and causing poor performance.
Attempted solutions:
3) Removed and inspected head. Replaced two galled valves and guides. Checked valved clearances several times.
4) Compression check (front to back): 130; 130; 129; 140. This was pretty much the score before the problem arose. I believe #4 is getting a little extra oil resulting in a higher number.
So is it time to pull the cam? Could I have flatted my lobes with my sticking valves?
[/ QUOTE ]
The suggestion to check ALL of the cam lobes for uniform lift with a dial indicator is good.
Why did you only replace two valves & guides? The problem really sounds like you still have intermittent sticking/leaking valves.
D
jlaird
Great Pumpkin
Offline
How about the throtle return spring, all free and nice?
Does it lope at idle? If so plug the vacume line and see if it still does it. If so there has to be air getting in someplace. From what you said I supose that the electricals are all ok and that fuel delivery is fine as well.
It must be air somewhere, try the carb cleaner spray trick again. Throtle rods, all gaskets, and the intake manifold as well gaskets and the body. Tis leaking some place.
Does it lope at idle? If so plug the vacume line and see if it still does it. If so there has to be air getting in someplace. From what you said I supose that the electricals are all ok and that fuel delivery is fine as well.
It must be air somewhere, try the carb cleaner spray trick again. Throtle rods, all gaskets, and the intake manifold as well gaskets and the body. Tis leaking some place.
OP
Morris
Yoda
Offline
Mark: Timing chain is brand new. I haven't pulled the cover since I started having these issues. I am sure that is in my future though.
Trevor: I am not using TPS. And my ignition timing looks pretty good. Mebee .25 degree drift in either direction.
Alan: That article was awesome! Thank you! I have read several vacuum diagnosis articles but none as thorough as that.
Dave: all valve guides are new (about 600 miles old). Two of the guides either came from VB messed up or were messed up by the machine shop during install. The machine shop claimed to have checked over the rest of the head when they installed the two "new-new" guides. But I now know them to be totally worthless. They did not even bother to seat the two "new" valves I gave them (they were from another head I had). I had to do it myself. *SNAP*. I bet that's the problem! I probably did a poor job seating those valves!
Nial: I will definitely try your trick of checking the lift. Thanks.
Jack: I soaked everything with ether this afternoon... again. I got a slight response from the manifold gasket. I tightened it but the problem persisted.
A little good news...
I put a vacuum baffle I improvised in and took her for a test drive and she performed quite well. Well enough to drive around for a while until I get the energy to work on it some more. I really need a little car enjoyment.
Trevor: I am not using TPS. And my ignition timing looks pretty good. Mebee .25 degree drift in either direction.
Alan: That article was awesome! Thank you! I have read several vacuum diagnosis articles but none as thorough as that.
Dave: all valve guides are new (about 600 miles old). Two of the guides either came from VB messed up or were messed up by the machine shop during install. The machine shop claimed to have checked over the rest of the head when they installed the two "new-new" guides. But I now know them to be totally worthless. They did not even bother to seat the two "new" valves I gave them (they were from another head I had). I had to do it myself. *SNAP*. I bet that's the problem! I probably did a poor job seating those valves!
Nial: I will definitely try your trick of checking the lift. Thanks.
Jack: I soaked everything with ether this afternoon... again. I got a slight response from the manifold gasket. I tightened it but the problem persisted.
A little good news...
I put a vacuum baffle I improvised in and took her for a test drive and she performed quite well. Well enough to drive around for a while until I get the energy to work on it some more. I really need a little car enjoyment.
jlaird
Great Pumpkin
Offline
"Jack: I soaked everything with ether this afternoon... again. I got a slight response from the manifold gasket. I tightened it but the problem persisted."
You do understand that the slight vacume leak at idle or low RPM will increase as you put a load on the engine.
Think I would work on that a bit not replace gasket necessarly but add a bit of gasket sealer and let it set up as the instructions say.
You do understand that the slight vacume leak at idle or low RPM will increase as you put a load on the engine.
Think I would work on that a bit not replace gasket necessarly but add a bit of gasket sealer and let it set up as the instructions say.
Offline
[ QUOTE ]
You do understand that the slight vacume leak at idle or low RPM will increase as you put a load on the engine
[/ QUOTE ]
Since engine vacuum is highest at idle & light loads, with the exception of coasting with the throttle closed, how would a "vacuum leak" increase as engine load increases & vacuun drops?
D
You do understand that the slight vacume leak at idle or low RPM will increase as you put a load on the engine
[/ QUOTE ]
Since engine vacuum is highest at idle & light loads, with the exception of coasting with the throttle closed, how would a "vacuum leak" increase as engine load increases & vacuun drops?
D
Offline
[ QUOTE ]
Less vacume at idle, really?
[/ QUOTE ]
No, more manifold vacuum at idle. Greater suction on the leak. Progressively less as the engine is loaded / throttle opened, The effect of a small vacuum leak would be greatest at idle & progressively less as the throttle is opened with engine load.
A given "leak" would flow much less percentage of the total air flow as the throttle is opened & the total air flow greatly increases.
D
Less vacume at idle, really?
[/ QUOTE ]
No, more manifold vacuum at idle. Greater suction on the leak. Progressively less as the engine is loaded / throttle opened, The effect of a small vacuum leak would be greatest at idle & progressively less as the throttle is opened with engine load.
A given "leak" would flow much less percentage of the total air flow as the throttle is opened & the total air flow greatly increases.
D
aeronca65t
Great Pumpkin
Offline
I'm still going to suggest a stone-cold and then hot compression test.
If that yields no big differences, then I'd do a leak-down.
Considering your previously reported valve-guide problem, I have to wonder if it wouldn't eventually be a good idea to pull the head and ream the guides....just thinking out loud here.
If that yields no big differences, then I'd do a leak-down.
Considering your previously reported valve-guide problem, I have to wonder if it wouldn't eventually be a good idea to pull the head and ream the guides....just thinking out loud here.
OP
Morris
Yoda
Offline
So, if the car remains driveable, I think my plan is to keep it going until I save up enough to build my "dream head."
Ported, polished, flowed... Oh yeah baby, and roller lifters... and a hot street cam. [drools]
BTW, Jack, I had it backwards, too, until I took on this EFI project. So at least I am learning a few things...
Ported, polished, flowed... Oh yeah baby, and roller lifters... and a hot street cam. [drools]
BTW, Jack, I had it backwards, too, until I took on this EFI project. So at least I am learning a few things...
Offline
[ QUOTE ]
So, dizzy vacume advance provides lots of advance at idle tapering off as far as weights and spring will allow at full throtle?
[/ QUOTE ]
Pretty much so. There are two main types of advance vacuum. The first one takes distributor vacuum directly from the manifold & would work as you say.
The second type (ported vacuum) takes distributor vacuum advance from a location that is slightly outboard from the throttle butterfly. This allows zero vacuum advance at idle but applies full vacuum as the throttle is advanced a bit from idle. Some engines idle better & have lower emissions if there is not full vacuum advance at idle.
A few systems even vacuum retard at idle & then progressively vacuum advance as the throttle is opened. It's all related to various emission control theories, of which there have been many. The retard at idle is based on the idea that the carb will give better mixture vaporization if the throttle is open a little more than normal at idle but this would cause the idle to be too fast unless timing was retarded to compensate.
D
So, dizzy vacume advance provides lots of advance at idle tapering off as far as weights and spring will allow at full throtle?
[/ QUOTE ]
Pretty much so. There are two main types of advance vacuum. The first one takes distributor vacuum directly from the manifold & would work as you say.
The second type (ported vacuum) takes distributor vacuum advance from a location that is slightly outboard from the throttle butterfly. This allows zero vacuum advance at idle but applies full vacuum as the throttle is advanced a bit from idle. Some engines idle better & have lower emissions if there is not full vacuum advance at idle.
A few systems even vacuum retard at idle & then progressively vacuum advance as the throttle is opened. It's all related to various emission control theories, of which there have been many. The retard at idle is based on the idea that the carb will give better mixture vaporization if the throttle is open a little more than normal at idle but this would cause the idle to be too fast unless timing was retarded to compensate.
D
OP
Morris
Yoda
Offline
Not clear on what you are asking.
With a ported vacuum source, there is no vacuum going to the vac advance at idle. So I set my idle advance to 10 (or whatever) and the vac advance does not affect that. Whether the vac advance is working or not, my idle advance is 10.
As I understand it, vac advance mainly affects emissions and fuel economy. The affect on performance is hardly noticable. But I could be wrong on that statement.
With a ported vacuum source, there is no vacuum going to the vac advance at idle. So I set my idle advance to 10 (or whatever) and the vac advance does not affect that. Whether the vac advance is working or not, my idle advance is 10.
As I understand it, vac advance mainly affects emissions and fuel economy. The affect on performance is hardly noticable. But I could be wrong on that statement.