Rocker arms breaking...

Post by **TDaxGav** » Sun Nov 13, 2005 5:05 pm

Okay,

This is turning out to be a VERY frustrating build, I obtained an old MG Metro Turbo engine, with the idea of using it build up a nice engine for the Morris... as it turned out the crank's could not be swapped since they were different sizes..

In the end decided to stick with the standard block (1098cc), and just use the mg turbo head... After opening up the water ways to mate up correctly....

All went well, started up on the button ran a lot healthier with the bigger valves.. went out on a test run and it snapped the turbo head's rockers (one of the forge aliminium ones), put the old the set of rockers off the original 1098cc head on, and within 2 hours it snapped the steel rockers....

Took the head off the engine, completely rebuilt the head, valves lapped in, valves polished and narrowed... the head has been ported and polished.. including grind into the head face to angle the spark..

Engine was running sweetly on idle, had a lovely burble, sounding very sweet.. Double checked everything, set the tappets to 12thou, top up the fuel tank with Tesco 99 Octane...

Car was running well until guess what, it snapped the third set of rockers.....

Any ideas what would cause the rockers to snap... have checked everything... valves are all still clean, pistons show no marking...

Has anybody got a clue why the same rocker is getting snapped OVER and OVER..every time it is the same one.....

I'm might go back to working on my 3l supra engines that I'm used to...

Gav

Post by **Matt** » Sun Nov 13, 2005 5:14 pm

Presumably you are using a 12g940 head for a large bore (1275 motor). Its possible the valve are just contacting the piston/block and this could make it break! Try taking the head off and put an thin layer of placticine on the end of the valve, turn the engine over on the handle and see if you can see any impression on the plasticine....

Post by **Onne** » Sun Nov 13, 2005 5:21 pm

he writes he is using the standard head

Post by **TDaxGav** » Sun Nov 13, 2005 5:23 pm

It isn't the standard head on the engine..

The block is a 1098 bloke
The head is from an mg metro turbo with the big valves (the valves that are fitted to the standard head)....

Will be taking the head off by the looks of it... and looking at a complete engine transplant, either a 1275 or a 1500 and then use this engine for a build over time project... probably take the carb off it and put a fuel injection system on it.

Gav

Post by **Matt** » Sun Nov 13, 2005 5:23 pm

No he says he is using the metro turbo head, which is a 12g940 designed for a big bore engine

Post by **TDaxGav** » Sun Nov 13, 2005 5:30 pm

Just had a quick look at the old head gasket and there are no marks from the valves bouncing on it or anything...

Just taken the rocker cover off to have a look, and this time it is actually a different rocker that has snapped, one over in fact....

Could the pushrods be too long?

I restate my previous statement, give me a supra 2JZ any day....

Gav

Post by **bigginger** » Sun Nov 13, 2005 5:31 pm

A what? What's a 'Supra'?

Post by **TDaxGav** » Sun Nov 13, 2005 5:33 pm

Supra..... I've got two toyota supra MKIV's...japanese sports car, mine runs around 500bhp.... but the morris is the father in laws so I've been working with him to get it running sweetly...

http://www.mkiv.com/mkiv_gallery/index.html

Gav

Post by **bigginger** » Sun Nov 13, 2005 5:33 pm

Just Googled it - It's a little Toyota. Hmmm...

Post by **TDaxGav** » Sun Nov 13, 2005 5:36 pm

It's a little Toyota. Hmmm...

Hmmm, don't know about little, but then I can see the charm in morris minors as well, even if they aren't my preferred car of choice...

Saw some nice minors up at the rally this year....

Gav

Post by **Matt** » Sun Nov 13, 2005 5:38 pm

Gav, is it a standard cam and rockers?

Post by **TDaxGav** » Sun Nov 13, 2005 5:39 pm

Gav, is it a standard cam and rockers?

Yes, the block itself in the car has not been touched... it is completely standard 1098cc...

You thinking the cam durations may not suit the metro head?

Post by **bmcecosse** » Sun Nov 13, 2005 5:46 pm

The problem is that the exhaust valves are hitting the block ! The bores are not big enough to let the valve slide down - I bet it is all exhaust valve rockers that have ben snapping. You can either cut the valve seats down by 40 thou in the head - or make little 'pockets' in the block under the valves - but either way you must get clearance. the engine will also run better if you can get an MG Metro camshaft - note the turbo camshaft is slightly better than a standard Minor camshaft - but not enough to be worth changing - the one to get is the standard Mg metro cam.

Post by **TDaxGav** » Sun Nov 13, 2005 5:51 pm

Hmmmm....

Would an additional head gasket get round the issue, just thinking it would be a lot easier than trying to grind into the block...

I think the current plan is to rebuild the standard 1098cc head and simply reinstall it back on...

Then I will rebuild a new morris engine on the bench with the mg turbo cam, mg turbo head, and put oversized pistons in the new engine... and then finally top it off with a fuel injection system...

Father in law is not a happy man with it snapping rockers...so revert back to stock for a while.

Thanks for all your help tho guys.

Gav

Post by **rayofleamington** » Sun Nov 13, 2005 5:57 pm

Would an additional head gasket get round the issue, just thinking it would be a lot easier than trying to grind into the block...

Probably not.
It may have bent the valves - I've run the 12G940 on a 1098 but it does need the valves to be seated further into the head. Pocketing the block sounds drastic but according to BMCEcosse it is really easy.

Post by **bmcecosse** » Sun Nov 13, 2005 6:01 pm

No - double head gasket very BAD idea ! Easiest thing is to sink the exhaust vlaves into the head by 40 thou - then no mods to the block. Turbo cam is pretty much useless unless you are going to be turbo-ing the engine. Far better with MG Metro non-turbo cam. the turbo head has very unusual (= expensive) sodium filled exhaust valves with thicker stems than normal. Otherwise the head has no advantage over a normal 12g940 head - you may do better trying to sell it to someone who can make use of the valves - although you may very probably have bent them with your 'adventures'. In general the Mini lads would give their right arms to NOT have fuel injection on their cars - so consider this very carefully. far better with the big single 1.75" SU off an MG Metro - with the inlet manifold. Again - note the Turbo inlet manifold is useless - it is specifically badly designed (log style) to build up some resistance and ensure good fuel/air mixing and fuel evaporation when used with the turbo - it's hopeless for a natural induction set-up.

Post by **TDaxGav** » Sun Nov 13, 2005 7:18 pm

Any guides or how to's regarding the pockets in the block?

Thanks

Gav

Post by **TDaxGav** » Sun Nov 13, 2005 7:51 pm

bmcecosse... thanks for the detailed write up...some good points there, we aren't using the turbo manifold, we stayed with the existing one..

I didn't realize the valves where sodium filled... the head is coming off anyway and the stock one going back in, and we are going to build up a bigger engine without resorting to hybrid/frankenstein style creations...

I've checked all the valves are they are dead straight (thank goodness)... but the head isn't going to be going back on this block...

Thanks

Gav

Post by **bmcecosse** » Sun Nov 13, 2005 10:04 pm

The little pockets can be (slightly crudely) ground into the block under the exhaust valves with just simple grinding stones in leccy drill. Of course - you need to seal off all the engine against ingress of stone dust/cast iron - and clean everything away afterwards. It really is much easier to simply sink the exhaust valves into the head by 40 thou. Of course this loses a tiny bit of power - but the gains from the head will out-weigh this no problem. I had my toolmaker at work do this on a head for me - it took him all of 5 minutes to do all 4 valves - he simply used a large 45 degree countersink in a vertical drill - great job. You also need to be sure to use 1275 rocker gear with a 1275 head - the valves are on slightly different centres - if you use 948/1098 rocker gear the rockers don't line up with the valves correctly. You can however strip and re-align the small bore rocker gear - it just takes a while !! Much easier to use 1275 gear.

Post by **Alec** » Mon Nov 14, 2005 7:39 pm

Hello Bmce,

I still feel that pocketing the valves is a bad idea, you significantly shroud the valve, decrease the compression ratio and misalign the valve to rocker geometry. Pocketing the block is a far better solution.

Alec