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how do I know if I need to rebuild my engine?

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MKramer Matthew Kramer
Ann Arbor, MI, USA   USA
Finally decided to post on this because, as much fun as a full engine rebuild would be, I would like to have a little time behind the wheel to fall back into love with the car before I devote myself to it.

74 Midget - first time midget owner - handy - non mechanic - done alot on other cars but don't know terminology and always have to learn as I go in new things - sometimes even things I used to know.

owned car 3 yrs approx. It was pretty hacked when I bought it but I felt sorry for it and wanted to learn new (Brittish car) things and wanted something that would take up less space. Best it can tell, original engine miles like 60-70k. Had a weber carb., electronic fuel pump, matte black spray can paint, sawed off bumpers, no top, etc. There were many parts for the car and extra in boxes came with the car. SU carbs were in a million pieces in boxes. ( I had never seen SU carbs before)

It ran rough when I got it and leaked everywhere. I removed engine and replaced seals, clutch and related parts. Found a bent distributor shaft that was probably making it a 3 cyl. Fixed most of that and speedo gear, put engine back in with weber and drove for a while - life was good. Pulled the body off and fixed all that, painted, replaced rubber and all door and window parts (stuff I knew how to do) and drove it for a while. Life was good and I was falling in love with the car.

It never ran very well as higher rpm and spit and sputter and sometimes fart.

One day it just stalled and died. I was able to limp it back to the house and tried everything to adjust carb, points, plugs etc.

Decided to rebuild SU's and replace weber. Did that (lots of learning and fun there) After installation, car ran but only at idle for a little bit. Did all the adjustment and setup routines. pulled plugs - relatively new and black, replaced and reset everything. The car would idle rough but stay running - lots of gas in the exhaust but would not power up with throttle.

Checked compression on all 4 cyl. 1-150, 2-160, 3 -155, 4- 120/125

Would prefer not to do a complete rebuild yet if I can do something to get it on the road and enjoy it until next winter. Rebuild would be fun, but I would be more excited to do it if I loved the car again.

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NOHOME P P
O, ON, Canada   CAN
1967 MG MGB GT "Maggie (GT From Hell)"
Best indicator of engine core health is a "leak-down test". it will tell you as a percentage what amount of your compression is escaping the cylinder. It will also with a bit of attention, tell you if it is going out the valves or the rings.

A poor mans version would be a compression tester to make sure you have reasonable compression in all cylinders and that none vary by a huge amount. Generally, if the engine has good compression, it can be made to run acceptably well; it may smoke a bit or a lot, but it should run OK.

Another useful tool is a vacuum gauge. Cheap to buy an it will tell you a lot about the core health of the engine. Quick Google search will lead you to tutorials on how to use a vacuum gauge to learn all about your engine's core health.

Pete

maraud Avatar
maraud Gold Member Sean K
Longwood, FL, USA   USA
With #4 being so far off the compression readings on 1-3 I would honestly be looking at the head, specifically the valves. Again, just a guess, but you may have a damaged / worn out spring, bent valve stem, or perhaps the valve seat is somehow damaged. Very well might the rings, but I'd start with the head myself.



Edited 1 time(s). Last edit at 2018-02-14 01:44 PM by maraud.

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MKramer Matthew Kramer
Ann Arbor, MI, USA   USA
So - to be clear - I am not afraid of learning and am fairly persistent and want to be independent (want to learn and do it myself) but there are a lot of things people talk about on this forum that I don't understand and feel stupid for it.

Also - I would really enjoy a complete rebuild of this engine, but feel like I would have a lot more motivation if I had recent memories of how it felt shifting from 3 to 4 with the pedal down.

I think I have a vaccum and pressure testing unit that I have never used. Don't know how to use it. Also, I have watched the leak-down tests online and have compressed air, but no tester. I would have to watch again

In anyone's opinion, could my problem be related to maladjusted valves? If I readjust them all, could that be it.

Alternatively - as someone has said, could I focus on the head? Replace a valve stem, spring and be ok - what is the probability? I would like to do everything to rule out an rebuild that is anything but for fun.

Chas 906 Avatar
Chas 906 Chuck Peterson
Iron Mountain, MI, USA   USA
1961 MG Midget MkI "Little Red Rider"
Never feel stupid about asking for help here. These guys are the best and have been there themselves. Start with a compression test of the four cylinders then report back with the results.

dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
You're over-thinking this. Your compression readings are entirely adequate for good street performance, even at higher rpm's. Other than your compression readings, which do not point to a particular performance problem, what is your oil pressure at hot idle and what oil are you using?

Your compression is OK. If your oil pressure is similarly OK, then your performance problems are most likely related to the overall state of tune of both your ignition and fuel systems. It may be worth your while to have a professional go through the tuning process, especially if you can watch and learn as he does. An alternative would be to find a local club member who is knowledgeable and willing to walk you through a thorough and proper tune.

If you do, you'd better have some good beer, and maybe a few extra shekels, around to show your gratitude... winking smiley

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

ice Avatar
ice Gold Member Larry Ice
Lawrenceville, GA, USA   USA
Mat, start with a good LBC manual, read how you tune up the engine and start from there. Like Sean mentioned valves would be high on my list of usual suspects. Not a big deal to pull the head and check it out.



Iceman

Atlanta GA

60 AH MK1
62 AH MKII
67 Midget
71 Midget

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zabond Russell Meehan
Neerim East, victoria, Australia   AUS
1966 MG Midget "Bridget"
remove the spark plugs, put 2 or 3 squirts of oil from an oil can into #4 cyl, rotate the engine a couple of times on the starter then do a comp test on that cyl, if the comp reading comes up then you have a ring problem, if it stays low its valve leakage, check the valve clearance, if clearance is ok you would need to do a valvegrind
Russ

S1 Elan Kurt. Appley
Akron, Ia., USA   USA
In reply to # 3681362 by zabond remove the spark plugs, put 2 or 3 squirts of oil from an oil can into #4 cyl, rotate the engine a couple of times on the starter then do a comp test on that cyl, if the comp reading comes up then you have a ring problem, if it stays low its valve leakage, check the valve clearance, if clearance is ok you would need to do a valvegrind
Russ

X2!

Worn out engines are a relative thing. I have a friend with a MGB who gives them a Rislone treatment and then loads them up with Lucas oil treatment. Drives them till they won't go and then fits another one.

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pixelsmithusa Avatar
It could be incorrectly adjusted valves, but that's and straightforward and simple fix. I agree with Dick; listen to his advice. It sounds like to have some tuning issues, especially with the carbs, but electrical issues sometimes mimic what seems like fuel problems and vice versa, so get that sorted out first. SUs are simple but require the right procedure in the right order to get dialed in correctly. I leakdown test will be helpful, but Russell's approach would give you an idea as well. The thing about a leak down test is it will give you a better idea how bad the problem is.



Gerard

http://gerardsgarage.com/


jmac Avatar
jmac Silver Member Jere McSparran
Greenup, IL, USA   USA
1978 MG Midget "Therapy"
1978 MG Midget "(SOLD)"
In reply to # 3681357 by dickmoritz You're over-thinking this. Your compression readings are entirely adequate for good street performance, even at higher rpm's. Other than your compression readings, which do not point to a particular performance problem, what is your oil pressure at hot idle and what oil are you using?

Your compression is OK. If your oil pressure is similarly OK, then your performance problems are most likely related to the overall state of tune of both your ignition and fuel systems. It may be worth your while to have a professional go through the tuning process, especially if you can watch and learn as he does. An alternative would be to find a local club member who is knowledgeable and willing to walk you through a thorough and proper tune.

If you do, you'd better have some good beer, and maybe a few extra shekels, around to show your gratitude... winking smiley

Dick

Dick said what I was thinking. This engine doesn't sound too bad. I'd give it a good tune up and valve adjustment and then drive it till the wheels fall off.



JMac
JMAC Engine Shop
http://www.jmacengineshop.com

MKramer Matthew Kramer
Ann Arbor, MI, USA   USA
when I can get to it, I will try to adjust the valves, test again and then proceed with other things. Is it possible that bad valve adjustment could cause both compression and rich fuel mix? I worked a long time on the carbs and many many adjustments according to a lot of the site experts here.

jimandcassdavis Jim Davis
Swanton, OH, USA   USA
Run through the checklist
Adequate spark?
Points set correctly?
Timing?
Advance working? Vacuum leak?
Compression?
Valve adjustment (start loose)
Adequate fuel pump ok and new filter
Carbs
Pistons move freely?
Floats set correctly?
Needle adjustment? start lean and richen as needed
Carb synched?

Good Rule: if you hear hooves think horses not zebras

GeorgeOhr Nonya Business
Yes, confused, USA   USA
When it stops leaking oil. winking smiley

S1 Elan Kurt. Appley
Akron, Ia., USA   USA
If you have been through the carb setting and adjusting procedure and everything stays rich try turning on you key so that the fuel pump is running. Then lift each carb piston with your finger and see if gas is running out of your jet. I'm suspecting a leaking float valve.

Kurt.

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