MGB Worrisome compression test results on my MGB 18GK

[davester]

I certainly wouldn't pull the head until I had done a leak down test to figure out exactly what the problem was. If you can find a mechanic who's experienced with leakdown tests, use him. However, bear in mind that there are a lot of mechanics who are clueless about this, or worse, they think they know how to do one but don't really.

Here's a link in case you want to do it yourself. https://www.xs11.com/tips/misc/misc3.shtml

 

[AweMan]

Re: Worrisome compression test results on my MGB 1

Valves that are too tight {Or Burnt} can cause compression loss!
Valve guides or guide seals, I wouldn`t think would cause any significant compression loss. {Unless the guides were EXTREMLY worn then it would smoke blue smoke horrendiously on start up}
All of your wet cylinder test came up {Increased} about the same percentage compared to the dry test. This to me indicates that although the rings may have some wear, they are serviceable.
The only other thing that would cause a compression loss would be a blown {Between cylinders} head gasket. And YES it could be leaking between cylinders and not leaking coolant into the cylinders or oil.
Tight valves would prevent the valve from completely closing during compression hence the loss of compression through the valve or valves.
loose valves, although they would make noise, would NOT cause compression loss at all. Although if they were extremely loose may cause low compression readings. {they would be extremly noisy while the engine was running} {If it ran at all}.
My suggestion is re-adjust the valves {a little loose is better than too tight} then redo the compression test both dry then wet. If you get the same result as before {Variation between cylinders} it is time to remove the head and check the gasket and valves for a burnt condition.
A leakdown test will tell you, you have a problem {but then you already know that}.
I was taught the "Old School" way. Initial adjustment, engine off, rotate the engine until each valve is completely closed and make each adjustment.
Once this is completed, start the engine bring it up to op temp and re-adjust each valve engine running at idle and up to op temp. {Solid lifters only}
{Hydrolic lifters are a whole different ballgame}
Just my nickles worth on this subject.
Kerry

 

[davester]

Re: Worrisome compression test results on my MGB 1

A leakdown test will tell you, you have a problem {but then you already know that}.

I beg to differ. If done properly, a leakdown test can pinpoint where the leak is occurring (i.e. if it is a burnt valve, and which one for example), and is a lot less hassle/expense than yanking the head. Personally, I like to feel very confident of the problem before ripping things apart.

 

[vping]

Re: Worrisome compression test results on my MGB 1

How does one perform a Leakdown Test?

 

[jlaird]

Re: Worrisome compression test results on my MGB 1

But but, that's all well and good but we know it is the valves and the only way to get to them is pull the head, shrug.

I tend to get right to the nitty gritty.

 

[tony barnhill]

Re: Worrisome compression test results on my MGB 1

I don't know that its in the valves!

 

[jlaird]

Re: Worrisome compression test results on my MGB 1

Hmm, seems that numbers 3 and 4 are low both on dry and wet compression checks. Wet check, as I understand these things seals the rings, sooooooo.

Please correct me if I am wrong folks. Never too old to learn.

 

[tony barnhill]

Re: Worrisome compression test results on my MGB 1

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Wet check, as I understand these things seals the rings[/QUOTE]

His numbers:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]DRY:

#1 1st- 149lbs 2nd- 149
#2 1st- 145lbs 2nd- 145
#3 1st- 107lbs 2nd- 107
#4 1st- 130lbs 2nd- 130

WET:
#1 1st- 155 2nd- 158
#2 1st- 155 2nd- 155
#3 1st- 126 2nd- 125
#4 1st- 143 2nd- 143[/QUOTE]

After adjusting valves:

Afraid it didn't make a huge difference though:
#1 157 157
#2 155 154
#3 128 128
#4 143 141

That's what I also thought & his went up minimally after he did the wet check & basically not at all after adjusting valves, sooo....

 

[jlaird]

Re: Worrisome compression test results on my MGB 1

Yep, not to say a complete rebuild is not in order but then the low #s 3 and 4 even with the wet check lend me to beleive that a quick fix for awile of course is the valves or the valve guides or both.

 

[davester]

Re: Worrisome compression test results on my MGB 1

How does one perform a Leakdown Test?

Look at the link in my post above yours.

I'm also thinking that Jack is probably right. Just different philosophies I think. After decades of owning/working on sports cars, I'm a bit gun shy of ripping things apart before I've nailed things down. I've done it before...tear things apart, fix what I thought was wrong, put it back together and still have the same problem...then listen for the curse words echoing around the garage.

 

[tony barnhill]

Re: Worrisome compression test results on my MGB 1

That's my point - when I take it apart, I want to know as positively as is possible what the problem is...it could e valve seals, it could be a bad head gasket, it could be a bad valve, it could be a broken ring...not enough info yet to pull head, IMHO.

 

[RonMacPherson]

For more precise diagnosis, the next step is a cylinder leak down test. Or pressurizing the cylinder at top dead center and listening to where the air is escaping, intake, exhaust or oil filler cap.

The evidence is suggesting top end(cylinder head), may also be ring wash or wear, due to the smoke.

 

[wkilleffer]

Here's what happened when I started the car this morning. When it first started running, there was no smoke at all. I didn't get smoke until it had been going for about 5 seconds, then it put out some dark gray, petrol-smelling smoke. I'd pulled the choke too far. I adjusted it, the engine smoothed out, and the smoke disappeared. Since I was driving the car to school, there was no chance to do another compression test while it was still cold and dry.

I'm about to take it on a run on US-11 between Chattanooga and Trenton, GA to see if I can carefully blow it out a bit.

Several years ago, I had the chance to drive a B that had a burnt valve. That's part of why it was for sale. I remember it well. The engine ran roughly with a distinctive popping sound. It blew smoke all the time and lacked power. My car's not like that. The idle is inconsistent at times, but that could be a fuel system problem. When driving and working through the gears, it sounds fine. It might could be more powerful, but it's not a dud by any means.

You don't know how furious I would be if a full engine rebuild was needed at this point after less than 15k miles. There might have been some things that I could have done better, but I don't see how I could have made a complete wreck of things. The company that rebuilt it has a good reputation in this area for their rebuilds. I could deal with the inconvenience, but the money's just not there now. I really don't see how this could happen.

Even though head work's not the easiest, I'm hoping that's all that's wrong.

Thanks,
-Bill

 

[piman]

Hello Bill,

15,000 miles is very little on a rebuilt engine which is why I suspect it is no more than just carboned up. If the valve clearance was that tight that it had burnt a valve you would have minimal compression on that cylinder. You have nothing to lose by giving it a hard drive.

Alec

 

[AweMan]

Re: Worrisome compression test results on my MGB 1

Adjusting the valves would not help at all if there is a burnt valve or headgasket problem.
The only cylinder that significantly increased wet was #3 It Could have a ring problem {cracked or broken}
If it isn`t a valve problem, it HAS to be a ring problem. Compression has NO WHERE else to go. {Unless there is a crack in the piston, head or cylinder wall} Other than through the guides and even if some compression is escaping through a guide it is MINIMAL and of NO consequence.

The bottom line is ....... I.M.H.O. the only way to fix whats wrong is tear down and inspect for problems.
I.M.H.O. it is CRAZY to run a NEW engine on synthetic oil.
At least "Break it in" first.

 

[wkilleffer]

Re: Worrisome compression test results on my MGB 1

Ok, I took the drive. It's about 20 miles each way, and that's all I had time for in between class. I didn't feel comfortable going much more than 70, so I would drive the speed limit for a bit, then gas it up to 70 really fast. I'd hold it there, then let it go back down, cruise for a bit, then get on the gas again. It pulls, and sounds growly and rumbly while doing so.

At the turnaround point, I stopped for gas and lifted the hood. There is definite seepage on the non-manifold side of the head in the gasket area. I've read that can be normal, but it seems odd. Is that a clue that the head gasket is bad?

If I pull the head, would I be able to look down at the cylinders and see visible trouble? I may call the rebuilder and see what they say as well. I don't mind pulling the head, but I remember changing the manifold gasket earlier in the year, and getting the exhaust to move out of the way was a real PITA.

As far as the oil goes, what I remember them telling me was that they put dino juice in it first, and that I should drain that at 1500 miles. Then, refill with 10w40 dino and drain again at 1500. After that, use 10w40 full synth and change every 2500 miles. They didn't require the synth, just recommended it. Should I use some 20w50 dino juice next oil change?

No matter what might be the trouble, it's irritating to think that something I did probably caused it. I'm not trying to avoid the blame, but learning the hard way is the worst thing.

 

[jlaird]

Re: Worrisome compression test results on my MGB 1

Sorry, no such thing as a normal head gasket leak.

Yep that's a clue for sure.

Like I said earlier I would pull the head, take it to my builder have the valves checked and have the head checked for level.

But before you do all that, retorque the head and see if it helps at all. If oil or water is seeping out can compression be far behind?

 

[AweMan]

Re: Worrisome compression test results on my MGB 1

A leaking head gasket is NOT GOOD! IF you decide to pull the head, have it magnafluxed for cracks. It isn`t uncomon to develope a crack between or under the valve seat surfaces especialy when replacing the valve seats. {I hope this is NOT the case}. Hopefuly all of the cylinder bores are nice and smooth. {No gouges or scrapes from a broken ring}.
IF a valve is burnt, you MAY {Or may not} see it, depending on the severity.
Were it me, I would take the head to a reputable automotive machine shop and have it thouroughly checked out {for cracks, trueness, and valve condition.} Also mention that the valve seats have recently been replaced and have them check the seats for any problems.
IF the cylinder walls show any gouging or scraping action therein may lay a broken piston or ring. all cylinder walls should be smooth with the exception of the honeing hash marks {very light marks left on the cylinder walls by the honing action}. These "Hash Marks" even dissapear with time and wear. So if there not there not to worry.
A piston ring can break very easily on instalation {especially the scraper 2nd ring or the compression, top ring} And not cause cylinder gouging or scraping But its rare.
The only way to check for a broken ring is {Sad to say} is remove the pistons from thier bores and inspect them.
IF your head turns out to be in REASONABLY GOOD condition then the rings are the next place to look for a problem.
I`m betting on the head, either gasket or burnt valve. {hopefuly not a crack}
Kerry

 

[tony barnhill]

Re: Worrisome compression test results on my MGB 1

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]As far as the oil goes, what I remember them telling me was that they put dino juice in it first, and that I should drain that at 1500 miles. Then, refill with 10w40 dino and drain again at 1500. After that, use 10w40 full synth and change every 2500 miles. They didn't require the synth, just recommended it. Should I use some 20w50 dino juice next oil change?[/QUOTE]
I wouldn't believe anything they told me! They might know how to assemble an engine but they don't know MGB's! The factory called for 20W50 from brand new...& I agree with Aweman: 20W50 from the 'git-go' & changed at 500 miles when you retorque the head then every 3,000 miles.

As for the weeping at the head, its either a head gasket, unlevel head, or cracked head...but, regardless of what any expert says, there's no such thing as a normal head leak! & don't try the rope trick!

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]If I pull the head, would I be able to look down at the cylinders and see visible trouble?[/QUOTE]
Only if there's visible scarring along the cylinder walls where a broken ring cut it...but that's not necessarily something you'd see.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I don't mind pulling the head, but I remember changing the manifold gasket earlier in the year[/QUOTE]
Why'd you have to change a head gasket on a newly rebuilt engine? That almost tells me something isn't level...did they deck the head (or block) before rebuilding?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]it's irritating to think that something I did probably caused it[/QUOTE]
Don't beat yourself up - its probably something the builder didn't do though you'll never be able to prove it....or its simply just a part that gave way.

If you do end up pulling the pistons/rods...be real careful that you put the rods in correctly - not necessarily how they came out! If they put a rod in backwards, you'd have oiling problems in that cylinder.

But the fact you've had to replace the head gasket worries me. & why would they change all the valve seats? That's just asking for leaks & cracks!

Aweman is probably heading in the right direction - at least doing that would eliminate head problems....but take it elsewhere than where it was repaired before! & have them magnaflux it, pressurize it, & check it for flatness.

If there's nothing wrong with the head, you're gonna have to pull the engine & think rering/rebearing....but its hard to tell what's what with the new info you just provided.

 

[wkilleffer]

Re: Worrisome compression test results on my MGB 1

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I wouldn't believe anything they told me! They might know how to assemble an engine but they don't know MGB's! The factory called for 20W50 from brand new...& I agree with Aweman: 20W50 from the 'git-go' & changed at 500 miles when you retorque the head then every 3,000 miles.

My memory could be faulty. You've heard of Rivergate up here, Tony? They're the ones that did the rebuild.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I don't mind pulling the head, but I remember changing the manifold gasket earlier in the year[/QUOTE]
Why'd you have to change a head gasket on a newly rebuilt engine? That almost tells me something isn't level...did they deck the head (or block) before rebuilding?[/QUOTE]

Not the *head* gasket, but the manifold gasket. I was beginning to think that I had a carb vacuum leak not involving the bushings nor shafts. So, I changed all the carb-related gaskets. It may be a fresh rebuild in terms of milage, but it is at least six years old from a chronological standpoint.

I know of one other person that I might could trust with a head examination, and that's John Rossi in north Georgia. I hate to keep harping on this, but I know so many people who were very satisfied with Rivergate's work. They seem to work on more Spridgets, but still... Won't know anything till I get the head off, and that might should wait till the semester break. Probably won't, but it should.