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MG Midget and Sprite Technical - Duplex timing chain kit. Will a Mini one fit?

I've been waiting for what seems like ages for a Duplex timing chain kit from Moss, who can supply everything except the cam wheel. They tell me there are none in their system at the moment. However, there are some on Ebay for Minis. So. Three questions. Will the Mini kit fit my 1098cc engine. Can I use offset keys with it and finally does anyone know the correct offset for a 731 camshaft? Thanks in anticipation.

Bernie.
b higginson

Yes, you can use the mini duplex - it's the same animal.

You need to replace the two hex-headed screws behind the crank sprocket with countersunk screws.

The offset key - if required - will depend on how accurately the keyways in crank, cam and sprockets have been machined.
Dave O'Neill 2

Bernie

For engine components forget Moss (unless you want crappy service and high prices)

every thing on the engine exept the front/backplate,crank and maincaps is the same as on a mini

minispares is verry good in sevice and price.

To answer your questions:

yes it will fit because it is the same kit.
If going from a simplex to a duplex chain the cover might need a small tap with a hamer since the sometimes foul the chain.

yes you can use offset keys to time a 731 cam

no no one can tell you what offset key to use that can only be determined by puting it in dot to dot and meassure the timing an then correct.

it is recomended to time full lift at 110 deg

Though i am running a 731 profile in my 1380 and just droped it in dot to dot (that is how it was fitted before) and it works great.

Next time the engine comes out i think i will go with venier timing gear and a diffrent cam but that is just because i can't help tinkering with it ;)

power is great now


Onno Könemann

if you want to avoid off set keys, go for the venier, it really makes timing a snap...If I remember I think you can just get the venier sprocket by itself thur mini spares... and not the whole kit if need be. and its considerably less expensive over there then here
Prop

Thanks guys.
Prop. I'm sure you're right about the vernier sprocket, but they are still quite expensive here too.

Onno. When you say you are going to try a different cam, which one are you thinking of and are you looking for outright high revs performance? My 731 is much better than the standard cam but is still quite useable at lower revs whereas a hotter cam might make it rather lumpy lower down.

Dave. I beleive the brake drum securing screws are suitable. Is this the case?

Bernie.
b higginson

I have moved cam timing a degree or 2 either way from desired/advised and have been unable to measure any difference on a rolling road.
As Duncan would say on Dragons Den (In a Scottish accent)

For that reason offset keys and verniers are a waste of time!
Robert (Bob) Midget Turbo

Bernie

Yes, 1/4" UNF IIRC, so should be fine.
Dave O'Neill 2

<< go for the venier, it really makes timing a snap >>

Yes, literally with a Mini Spares timing belt after only 3,000 miles!! Car due back at the end of this week from France, so will find out over next weekend what horrors I will find inside.

Needless to say I will not be using the timing belt kit anymore. Will check the timing using the as supplied 'dot-to-dot' and then either fit an offset key to correct if the error is <=4°, or otherwise a vernier chain kit if more.

Bernie,

The countersunk screws should be 1/4" UNF hex socket head Allen screws, brake drum screws are Phillips cross head - not sure if they will tighten enough, or if so might be difficult to get out in the future?

Richard
Richard Wale

Bernie

I am thinking of the Grayham Russel profile RE13 or anny thing in the 286/295 range
I don't mind cammy engine's and you cna compensate a bit with a higher CR (i have a verry high CR head in stock)
Onno Könemann

Richard. Thanks for the advice about the screws. I had been wondering if there might be a problem with cross heads not being tight enough. I hope you don't find too much damage in your engine. That's the problem with belts, they don't let you know via noise when they're going to go. At least a chain will tell you that it needs replacing.

From what I'm reading here, I may as well cancel the offset keys I ordered from Moss. Dot to dot it is then.

Onno. I've got a spare 12G295 head that I'm going to get gas flowed, so I'll ask the machine shop to take a bit off to increase CR. Then I'll probably get a different dissy. We just can't stop messing can we? LOL.

Bernie.
b higginson

Bernie

Do go for the offset keys they never harmed anny one and dot to dot is not always good there can be a lot of diffrence in timing even between the same cam from diffrent grind batches (especialy with regrinds)

I only timed dot to dot because it was previously fitted like that and worked fine.

Be carefull with that 12G295 they have some cracking habits (realy they crack)
And the have a lot of chamber volume since they originaly where used with D top pistons instead of flat or dished ones.
So they have to get a big chunk milled off which can not always be done considering the path of the oil ways.

If you have a 12G202 i would get that done since the 295 only gives you a benifit in standard form and the 202 is more reliable.

Onno Könemann

Hi, Robert (Bob) midget Turbo's comment about timing the cam not being measurable on the rolling road is the first time that I have ever heard that. In fact, most engine builders I have spoken with over the years have stressed the importance of getting the cam dialed in right, and their dyno results supporting it.

I wonder if there could be a factor on a turbo'd engine that would make it less sensitive for Bob, than is normal for a normally aspirated engine?

Norm "curious" Kerr

Norm Kerr

Nothing to do with Turbo mate, I have only done the turbo thing in the last year or 2.

Before that I have been racing and using A Series engines for about 40 odd years.

At one time I did a lot of work on cam timing and have stated my findings who has evidence from a rolling road to the contrary.? I would be very interested
Robert (Bob) Midget Turbo

I can't make an informed comment about the A-series, but I do know that on some engines the vernier timing is quite useful and some cams come with a chart to help you pick a starting place based on lift ratio and valve size and/or desired onset of powerband. The variance is often more than 2 degrees.

I have a vernier unit in my sprite. It allowed me to time it exactly as the cam grind specified. Does it make a difference? I don't know. Why didn't the cam grinder make the grind such that dot-to-dot would it to time as specified? I guess maybe because of the nature of the blank he started with.
Trevor Jessie

Yep must admit my research was not on a dyno but on a rolling road which I suppose is slightly less accurate than and engine dyno. Would love a couple of days playing with an engine dyno but spent a fortune on a rolling road for a couple of days many years ago.

The results of cam timing that I found were for a couple of degrees either side of "optimum", then advancing perhaps lifted the power band slightly (as you would expect) whilst retarding perhaps had the opposite effect.

In a championship that regulated the cam then having an offset key and advancing the cam a couple of degrees could maybe give an edge on power due to the raising of the power band. :)

Well thats how I convinced myself at the time. LOL
Robert (Bob) Midget Turbo

Onno. Thanks for the tips. I've sent the head away to be pressure tested first before I try and do anything with it, so nothing is certain yet. I'm in no hurry so maybe I can find a 12G202 in the meantime.

Bernie.
b higginson

This thread was discussed between 24/09/2010 and 29/09/2010

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