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MG MGB Technical - Pic of timing chain with tensioner

What do you guys think?

Samuel Sullivan

Samuel. I think, for what it is worth, that this is an image of an 18V engine (single timing chain) which has been rebuilt (note the yellowish, grade 8 bolts).

Please forgive me if I do not have the time to keep up on every thread, nor to read everyone's mind.

What do you intend here?

Les
Les Bengtson

Les-
This is Sam's third thread on this; see "GT lacks power" and "Pic of timing chain...".

It does look better in this pic, enough to make me wonder if it was changed between shots. I see that in the other pic the lockwasher was not yet bent up. However, the crank must be exactly at TDC for the alignment to be valid, and that cannot be determined from this picture either. It is simple to align the marks by just turning until they line up, but meaningless.
Read again my comments re marks in your original thread.
Do yourself a favor and do the quick check of valve timing as described.

FRM
Fletcher R Millmore

Fletcher. Thank your for the update. Been rather busy here lately.

I would agree with you that this tells us very little, other than that we are looking at, to me, a simplex timing chain of an 18V engine. Why use a simplex system when doing an engine rebuild? (Perhaps this is because Moss, et al, are using an improperly machined camshaft sprocket, as I have noted before?)

When the engine is built up as a short block, it is rather easy to dial in the cam. And, a very good idea such things are.

There are many things which can cause "loss of power" and "failure to perform to expectations". But, unless you know that the engine has been properly built, you can do nothing about anything. No amount of carb tweeking, nor any amount of "custom distributor mechanical advance curves" will retrieve an engine which is out of cam time. Basics are your friend--and the first place to look when there are problems.

When I build an engine, each step is a check mark on an list of "vital things". This includes the torque of each main bearing bolt, each rod bearing bolt, dialing (checking) the cam in relationship to the true top dead center, and every other thing that you do. Some of the are minor.

Check the surfaces of the intake and exhaust manifolds for straightness using a piece of steel. Make sure the nuts you are tightening screw down below the level of the surface you are sealing (or, below the surface of the washer that is the spacer between the surface and the lower portion of the nut).

Take nothing for granted that you have not checked, at least once, AND NOTED ON YOUR PAD OF PAPER WITH YOUR ASSEMBLY NOTES.

Made many mistakes in my life. Very few twice. (Other than the second marriage--and that is, most probably, not a mistake--rather fine, actually.)

Les
Les Bengtson

Sam
Now that you have moved the cam sprocket 1 tooth clockwise it looks correct. - congratulations you can put the cover on now. Don't forget the slinger first though Willy
WilliamRevit

I think you should post additions to your thread to the same thread, not keep creating new ones.

This looks correct to me (assuming dimples are correctly positioned as FRM warns). If this was taken after the other one, seeing as it has the crank nut lock tab bent over and the tensioner fitted, then the valve timing should be OK.
Paul Hunt 2010

I mean cam lock-washer. And judging by the keyway on the crank gear that at least is correct, dimple-wise.
Paul Hunt 2010

Thanks all. I am going to do the rocker test just to be sure.
Samuel Sullivan

Well I pulled off the valve cover and did the 3 & 4 rocking at TDC and they were rocking.
So I guess the cam and crank are in synch.
Compression test showed 175,150,165,150.
My LM-1 A/F meter shows the right readings for WOT and idle.
I have the dizzy timed back to about 8 btdc but still get pinging on hills
in 4th gear with rpm between 2500-3000. Downshift to 3rd doesn't seem to want to pull the weight, and then more pinging. I use Mobil and Shell gas 93 octane. There's a Sunoco nearby that sells 100 octane.
May try that but it's 9 bucks a gallon.
Any suggestions on what to try next?
Samuel Sullivan

Sorry that was 7 & 8 rockers not 3 & 4.
Samuel Sullivan

Has anyone had trouble with timing chains being sold as having a pitch in a fraction of an inch, but are really metric pitch equivalents?


Mick
M F Anderson

No - dodgey retailer I reckon
There is plenty of imperial chain about.
Willy
WilliamRevit

Is this a low compression engine or high? Very unusual to get pinking on a low, especially with only that amount of advance. Did you double-check the TDC pointer and mark against the piston position?
Paul Hunt 2010

What's the history of the distributor? It may be giving you way too much advance too soon in the rev range due to weak springs. RAY
rjm RAY

rjm
Itwouldn't be the first lucas dizzy with rusted (weak) or broken springs Willy
WilliamRevit

"Compression test showed 175,150,165,150."

Without knowing what might have been changed internally over time, these figures suggest a high compression engine if still anywhere near standard components.
Roger T

That's true, hence much more likely to pink. As I understand things America uses PON for octane and UK uses RON, and 93PON equates to 97RON which is one of the higher UK grades, and 7 or 8 is about as high as both me and a pal can go with that but still get a little pinking.
Paul Hunt 2010

This thread was discussed between 03/07/2010 and 06/07/2010

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