Midget engine rebore

[olderisbetter]

Can anyone recommend a sompression tester or even name any to avoid.

[oliver90owner]

Any that work are OK. I would never accept compression figures as an absolute value. They are basiclly there for a ballpark figure with the real use for comparing pots. Pots should be within 10% ideally. Anything better than that is icing on the cake. The actual accuracy of most any 'lower-end' pressure guage is probably worse than + or -10%.

RAB

[philthehill]

The Gunson's Hi-Compression Gauge is a good middle of the road cylinder compression gauge.
As above it is only a comparator of cylinder bore pressure but adequate for most needs
If I have to check cylinder pressure it is the Gunson that I use and which has given good service over many years.
Phil

[bmcecosse]

As Phil says - the actual readings are not too important - the variation between cylinders is what really matters to you - and is something you can then correct! There are plenty inexpensively on ebay that will do that job for you -and you can lend it out to mates!

[philthehill]

http://www.ebay.co.uk/itm/Gunsons-Hi-Ga ... SwzJ5XVUq3

at the other end of the scale cost wise:-

http://www.ebay.co.uk/itm/Sykes-Pickava ... w33ECMWXVA

[olderisbetter]

Thanks phil i have gone for the gunson version as my local machine mart sells them, and bmcecosse these days when it comes to tools i have no mates

[bmcecosse]

So now - let's see the readings! Nice hot engine and accelerator held down with a brick.

[olderisbetter]

Well i did the compression test this afternoon, i did it with a hot engine, all plugs out with carbs fully open and the did it again with a few drops of oil in each cyclinder and got
1. 185 first test 190 with oil
2. 190 first test 195 with oil
3. 180 first test 185 with oil
4. 180 first test 185 with oil
the plugs looked a bit sooty but not heavily coated, i did about 3 miles this weekend so it may be running rich but something just came up that when i put fuel in it was nearly full and it has been standing in a garage before i got it for over a year, i am thinking the fuel is no good, i also got the valve cover off and it does have a 940 head, i don't know if it has big valves or if midgets had them as standard, the only other number in side the tappet cover cover was 28D.

[Chipper]

They seem like very healthy compression readings to me - about the same as my 1275cc MG Midget engine (with Metro unleaded head) gives.

Perhaps it just needs a good old Italian tune-up, i.e., a damn good thrashing! And yes, fresh fuel always helps.

I know you said you'd changed the dizzy cap, HT leads, coil, plugs, etc., but it may be worth measuring each HT lead with a multimeter to ensure they're all within approx. 10,000 ohms (10k) or so, also ensure the engine-to-body earth strap is good - use the multimeter to ensure the resistance between the engine block and the body is close to zero ohms.

[philthehill]

The compressions are fair and I certainly would not do anything about the bores at the present time.
The rockers in your photo are not standard and appear to be roller tipped with a ratio of possibly 1.5.
I.5 ratio rockers do not suit all engines even the large bore ones.
If not already open up the valve rocker clearances to 15 - 16 thou. It may help.
The 1275cc Midget was fitted with the 940 head as standard and the inlet valves in standard form were 1.307" - 1.313" dia and the exhaust valves were 1.1515" - 1.565" dia.
Your head may have been modified and larger valves fitted.
Fuel that has been stood for some time goes off and its use can result in poor performance.
Unless you have a full spec for the engine your engine is a bit of an unknown quantity. Even the camshaft may not be standard which if mated to the wrong components can give a decrease in power.
Phil

[olderisbetter]

Chipper, i will do a test on the leads and use the meter to test for a good earth, Phil i will check and adjust the valve setting if need tomorrow and it does have a swiftune cam, so i will do all the simple/cheap fixes first, i have ordered a new manifold to fit my hif44 carb from minispares.com so that should make it easier for me to adjust the mix, and while i have the manifolds off it might be a good time to remove the head and have a peak inside.

[bmcecosse]

As above -the readings are all excellent. There is nothing wrong with your engine or valve seatings. And yes - I too would get rid of these rockers, especially with the SW07 camshaft - it's already high lift - the last thing you want is even more high lift! And open up the valve gaps - I ran at 18 thou.

[philthehill]

It is a good idea is to keep an engine log book of all the modifications you find and all the alterations you carry out.
Note the valve sizes and the cam number/details ect ect.
Easy to back reference and any future modifications can be planned around what has gone before.
There is nothing worse than spending money to find the part that you thought was going to give a fantastic boost in power does not work with the parts already fitted.
Phil

[olderisbetter]

Thanks Roy, i think when i do the carb change i will replace the rockers with standard types and they are listed in the paper work i have as 1.5 rockers.

[olderisbetter]

Phil from what has been said those 1.5 rockers are noisey and not needed but i think they are sold on looking pretty, i will keep a log to make it easier and i take pictures for reference on most things, i have just took it for a quick italian tune up but it still ticks over the same, oh well tomorrow is another play day for me.

[philthehill]

Those 1.5 rockers do work for some engines. I have full roller 1.5 rockers fitted to my 1380cc comp engine with a very extreme cam but the rockers are part of a complete package that gives in excess of 135bhp at the flywheel.
The package is no good for normal road use though.
Phil

[IslipMinor]

The same 1.5 rockers on our 1380, with a Piper 270 cam and running 0.014"/0.017" tappet clearances is very quiet, hence my previous comment about valve whirring! Definitely not thrashing, and probably quieter than the previous Kent 276 that needed 0.016" with standard rockers, so 0.018"/0.021" with 1.5 rockers, which is the same requirement as the SW7 Swiftune.

What clearances are you running and is there noticeable noise from the valve gear?

Before removing potentially perfectly good rockers, why not contact Swiftune and ask their opinion? They should know their cam's best setup better than anyone?

[bmcecosse]

Have to wonder why the adjuster screws are so far up in the rockers. You'll get good money for them from a Mini mug.

[olderisbetter]

Well i swapped the twin carbs for a single hif44 from a mini 1275 today and all went well but the darn thing does'nt run, I think it needs a carb strip down and rebuild, I tipped some fuel into the inlet and it fired up and it did run for a few seconds is there a link to a rebuild or some info, i am pretty sure i have all the pipes on the right way round

[bmcecosse]

And the piston rises and falls ok? Since it runs with the 'tip' -it's obviously not getting fuel through... Maybe the float valve is stuck shut.