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MGB-GT Engine Problem 74MGB GT
- Thread starter jimz26
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Did you install new valves, by any chance? Or springs? What are the valve spring free lengths, and installed heights? I would have done a leakdown test immediately after finding the low compression numbers. Something here just flat isn't adding up.
Your ring gaps, if they are in the .025"-.030" range, are way too large, but not to the point to give you compression numbers as low as that. Did you by any chance have the head milled significantly. ie more than .050", and use stock pushreods?
We can chase our tails on-line on this one forever!
Dave, when the valves aren't open, don't you just assume 14.7 as ambient, and multiply by the compression ratio to get the proper numbers?
ONLY JOKING, FOLKS1
Jeff
Your ring gaps, if they are in the .025"-.030" range, are way too large, but not to the point to give you compression numbers as low as that. Did you by any chance have the head milled significantly. ie more than .050", and use stock pushreods?
We can chase our tails on-line on this one forever!
Dave, when the valves aren't open, don't you just assume 14.7 as ambient, and multiply by the compression ratio to get the proper numbers?
ONLY JOKING, FOLKS1
Jeff
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<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Bugeye58:
Dave, when the valves aren't open, don't you just assume 14.7 as ambient, and multiply by the compression ratio to get the proper numbers?
ONLY JOKING, FOLKS1
Jeff<hr></blockquote>
I guess so, but only if the piston starts exactly at bdc & stops at TDC. Kind of hard to get just 1/2 revolution on a test.
D
Dave, when the valves aren't open, don't you just assume 14.7 as ambient, and multiply by the compression ratio to get the proper numbers?
ONLY JOKING, FOLKS1
Jeff<hr></blockquote>
I guess so, but only if the piston starts exactly at bdc & stops at TDC. Kind of hard to get just 1/2 revolution on a test.
D
Well, I suppose either keep the intakes gapped, or cycle the tested piston to the bottom before testing, or something like that. The main idea is to work through a series of tests in a methodical order. If the gauge isn't bad, then it sounds like getting air in shouldn't be a problem in any case..
tony barnhill
Great Pumpkin - R.I.P
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Bugeye...we can chase ourselvesforever on this one, however...
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>did the valves and seats and they are new rings<hr></blockquote>
...if we could get more info on this statement, it might point us toward the head or block...what do you mean by "did the valves and seats"?
...&, I'm back, also, to what you did in the cylinders...as I understand, all you did was knock the ridge off the top & replace the rings???
....since different words apparently mean different actions to each of us, please walk us through what is different today than before you started on the car....
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>did the valves and seats and they are new rings<hr></blockquote>
...if we could get more info on this statement, it might point us toward the head or block...what do you mean by "did the valves and seats"?
...&, I'm back, also, to what you did in the cylinders...as I understand, all you did was knock the ridge off the top & replace the rings???
....since different words apparently mean different actions to each of us, please walk us through what is different today than before you started on the car....
The ridge I took off was small I honed the cylinders --------- I took off the head,it's warped between #2and 3 with a rule across and light behind can see light between head and rule.
i'll take it to machineshop tomorrow.Hopefully this will rectify problem.
Thanks JIM
i'll take it to machineshop tomorrow.Hopefully this will rectify problem.
Thanks JIM
tony barnhill
Great Pumpkin - R.I.P
Offline
It may have a slight warp but could still be pulled down with torque & a good gasket...plus, there's no guarantee the level is perfectly straight...only machine shop will tell...still, don't see how that could cause all 4 cylinders to be so low
Gary Lloyd
Jedi Knight
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I agree!! That has nothing to do with the real problem!! Get the machine shop to check the valves, but I would doubt that too!! Can you describe how you set the valves. It seems to me that you mentioned that when you messed with them the compression went up slightly!!
Gary Lloyd
Jedi Knight
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Well, what did the machine shop say????
Gary Lloyd
Jedi Knight
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I thought you said the valves were done???? It's starting to sound like a combination of things!! You will need new rings too, because the end gap is so large!! It's only a couple of hrs work to pull the engine out when the head is off!!! I wonder if you shouldn't pull it and take it to the machine shop!! I hope you didn't get in over your head!!
There would be nothing worse than getting it going only to have it blow up on you!!
tony barnhill
Great Pumpkin - R.I.P
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Gary...now you know how frustrated we got trying to help out long distance!
Gary Lloyd
Jedi Knight
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Tony, I think the hard part is when somebody says something is done, but for some reason or another it has to be re-done!! Like my balancing and the re-conditioning of my rods!! It was just not done properly by the first shop!! I still can't believe the tweek in that flippin' rod!!! They could never have balanced it!!!
Same here, if the valves have been done, but they have to be redone, how can you identify the problem??? I am now worried about the end gap, it sounds way to big for me, but I don't have the specs in front of me!!
Same here, if the valves have been done, but they have to be redone, how can you identify the problem??? I am now worried about the end gap, it sounds way to big for me, but I don't have the specs in front of me!!
Gary Lloyd
Jedi Knight
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It does happen sometimes Jim!!!
Be careful!!!!!
tony barnhill
Great Pumpkin - R.I.P
Offline
Jim....took he day off from school today to get all my orders caught up....yours has to go via US Post Office so have to get there before 3:30pm my time!
Garry, you're right, last one I blew was a 59 Porche on Harewood{airport track]
Tony, thanks.
I bought this car in NY in April from a guy that had it 6 months,and couldn't get it running.He got it from a guy that started work on it but------now 7years later. Last MG I had was a 57 coupe never had any trouble with it [ It was new then]
I put this on the Forum as this was a new one on me and thinking this was might be a problem familiar to MGs but it seems to be an isolated problem. NEVER BEFORE----Winston
Ta 4 now JIM
Tony, thanks.
I bought this car in NY in April from a guy that had it 6 months,and couldn't get it running.He got it from a guy that started work on it but------now 7years later. Last MG I had was a 57 coupe never had any trouble with it [ It was new then]
I put this on the Forum as this was a new one on me and thinking this was might be a problem familiar to MGs but it seems to be an isolated problem. NEVER BEFORE----Winston
Ta 4 now JIM
tony barnhill
Great Pumpkin - R.I.P
Offline
Jim...just got back from post office....Canadian mail is strange! I'm always perplexed about it....Anything under 4 pounds is real cheap, over 4 pounds costs an arm & leg! I left the bottom track on the glass in case you don't have one...