Compression Tester

[flashgit]

Can anyone recommend a value for money compression tester? This is for DIY occasional use so I'm not looking to spend wads of cash on something very sophisticated. It will be used on an MGB and a Mini to start with.

[v8250]

would this do the job?

http://www.amazon.co.uk/AUTOMOTIVE-PETROL-ENGINE-C...

[nta16]

I don't know about the one above but I've heard of a couple of cheap ones that don't even work when fresh out of the box

[flashgit]

Those on Amazon and eBay are the ones I have been looking at - the reviews are very variable which is what has prompted this thread - rather go by a recommendation here from an "owner". I'm happy to pay around £20 (+/- £2) to get something of reasonable quality :-)

[nta16]

from what I've seen you do need to know how to use the tester fully to get accurate results and then often the results are interpreted as giving absolute diagnostics rather than more accurately giving an interpretation of possible diagnostic results

[ATE399J]

Interesting this, firstly because l recently bought one from Halfords (£25) and had to take it back as it didn't work.

Anyway, just tested this evening as the "old girl" was popping and banging and lacking any power- I was thinking it was a burned out valve. Results of test, cold, dry, were 130, 122, 126 and 131. Just about within 10 psi of each other. I re-checked the timing and set it up with the vacuum advance disconnected. When l connect it the timing shifts by about 20 degs which, to me, doesn't sound quite right. Having set it up like that it runs much better but still misses when pulling from low(ish) revs and wide open throttle.

Any ideas as to (1)why the vac adv makes such a change and (2) why it won't pull on WOT??

[HumbleJim]

When setting timing on these old engines I treat the manufactures figures as guide lines. If your dizzy is worn it will make set up very difficult.

I advance the timing till it's pinking and then back it off a bit, but worth starting from scratch as per the manual.
Valve clearances, points, etc etc.

[v8250]

HumbleJim said:

When setting timing on these old engines I treat the manufactures figures as guide lines. If your dizzy is worn it will make set up very difficult.

I advance the timing till it's pinking and then back it off a bit, but worth starting from scratch as per the manual.
Valve clearances, points, etc etc.

This +1. Number of folk out there whose distributors are shot is remarkable. I have a friend with a GT. His distributor is the original from 1974. It's never been touched except for points and rotor arm. The thing drifts to every setting except 5degs TDC and has the most useless power curve known to man...it coughs, splurts, farts, bangs and always over runs on turning the ignition off. The answer's simple...buy a new distributor. And to make matters worse...it's a bloody automatic

So, OP, what's your compression like...any news?

[nta16]

I've read that the dissys were out within 2 or 3 years of the cars leaving the factory so imagine how they are after decades of use and no maintenance

then there is the question of how accurate the timing gun actually is

were the tappets checked at the start (then cb points, plugs)

[flashgit]

All, I see this topic took a stroll
I eventually got a £25 special from Halfrauds - the Gunson model, and did the test at the weekend.

I was warned to warm the car up to normal temperature beforehand and then did the "dry" test. I got 150, 140, 147, 156, so I'm well above the recommended figures and not far out on the 10% variance (140 + 10% = 154; 156 -10% = 140.4). As these figures were reasonable I decided that the "wet" test was not necessary. [I did notice something at this stage which I will return to later ...]

But, still getting the lumpy idle and misfire under load, I realised I needed to run through all the basics again. As I have thoroughly cleaned and serviced the carburetors in the last 6 months, and checked the dynamic timing and valve clearances as well, it left fuel filter check (clean) and electrics. Spark plugs are OK, HT leads swapped around to cross check and seem to be OK.

So, I had a spare capacitor/condensor to hand. So, opened the dizzy (original, so likely worn - comments noted), replaced the capacitor and whilst there removed, cleaned, replaced and setup the points again. Those familiar with this process will note the rotor arm needs removing to achieve this. When I tried to start the car again there was no joy. Removed and checked a spark plug - no lightning! Replaced rotor arm , car started and seemed to be running more smoothly on the subsequent road test.

[... and now back to the discovery]
A slight weeping of oil was noticed from between the head gasket and the cylinder head, but more strange was the small "bubbles" that were there as well. So, job for the weekend is to lift the head and replace the gaskets. I'm assuming and hoping that the head gasket change might improve the variance on the compression test figures.

I will update after the coming BH weekend unless I can't wait until then to do the job

[flashgit]

Change of head gasket completed and I now have a pressure range of 130-135. There is still an occasional misfire (more a hiccup). I will run the car a few more time to let things "bed in" before making any more changes (HT leads and spark plugs next)

[nta16]

you don't want to be changing parts just for the sake of it and you need to do a step by step diagnostics to find the cause of the misfire

but if you want very well made and good quality leads at a reasonable price (that doesn't mean cheap if you're the usual type of tight-fisted B owner) then 'performanceleads' by Fast Lane are it, they make leads for others to market as their own so only do retails sales through phone enquiries via their web site - http://www.performanceleads.co.uk/

also be aware of p*ss poorly made rotor arms that can cause faults, Distributor Doctor is a source of good quality dissy parts - http://www.distributordoctor.com/

NGK are the recommended plugs but if you want I have some top line Champion plugs I can sell you for a lower price