Backplate problems

[billlobban]

Is there any logical reason for a difference in two backplates from 2 different 1098 engines

Senario is this removed engine and just happened to notice that the backplate was cracked - still in one piece but cracked in 2 places (before you ask I was an Inspection Engineer for a number of years so I know what a crack looks like). No problem - thinks I - got the backplate on an 'old' engine I'll swap it over. - Now the real problem

The backplates are identical in every respect bar 1. Thickness, bolt holes, external shape all identical. Except the large hole for the oil pump which is ofset upwards by about 3/16ths and this means that it fouls the oil pump. It fits the engine it came off of (10MA) but wont go near the 'new' engine which is still a 1098 although originally from a late model low compression van.

Confused I am

Since there is no way the replacement backplate will fit can I weld the cracked one?

[Alec]

Hello Bill,
cast iron can be welded satisfactorily, but the problem could be distortion. If bolted to the back of the engine as a jig it may tend to cause stress to the weld as it cools. That said peening of cast iron welds is recommended I believe, to relieve stress.
The options are to machine some clearance for the oil pump if there is sufficient material or to mechanically strap across the crack to reinforce it. The gearbox will in some way do that but depending where the crack is?

Alec

[billlobban]

Hi Alec
Machining out the hole would seem to be a non starter as the oil pump cover would no longer fit properly.
I just compared both with the gasket which fits the cracked one perfectly and doesnt fit the 'new' one very well. So I guess its probably down to bad quality control. It didnt matter on the donor engine as it has a standard oil pump but I've fitted an MG Merto cam which meant changing the oil pump and its quite a bit bigger.

[bmcecosse]

It's quite common for these backplates to crack - you will know to drill holes at the end of the crack - and perhaps a few along it's length - groove it out on both sides - and stitch weld it up going from side to side in short bursts. Some of the later pumps are a bit bulkier - doesn't matter on a MIni - there is nothing behind the pump. You can safely file/machine some metal off the back of the pump - or look for a slimmer one! Not understanding your comment about a 'gasket' ??

[billlobban]

Not understanding your comment about a 'gasket' ??

The gasket between the backplate and the block Roy. It matches exactly the cracked backplate. But is nowhere near the 'replacement'. Too late for the holes I'm afraid cracks extend all the way across from the 'triangular' cut out behind the main bearing to the starter motor hole. One further up from the oil pump hole to the outer edge.

I'm surprised about the difference in the oil pump hole location. I'm too stingy to buy another new pump. so I guess its the welder I need more practise anyway so I'll give it a go

[polo2k]

I think its reccomended to preheat the casting in the oven and then a blast with a blow torch to reduce the stresses.
I think its quite straightforward with TIG and cast iron Rods.

You mentioned thickness. There is a user on here called pskipper and I was talking to him about this the other night. He found out the hard way that they arn`t interchangeable!

[RobThomas]

10CC serial number Midget engines had oil pump moved in relation to the crank. 10CC backplate fits 1275, also. Maybe your low comp engine has 12G432 or 435 cast below the oil primer plug? This is the 'big journal crank' engine. IIRC, the pump cover is also slightly larger diameter.

[Alec]

Hello Bill,

unless you have a source of cast rods it may be more cost effective to get a second hand one? What type of welder have you as a matter of interest?

Alec

[billlobban]

Alec - I've decided against the welding route - now I'm on the scrounge for another backplate.

Rob no such luck I'm afraid neither of them are 10CC engines worse luck. Ive just rebuilt the 10V low compression as high compression.

The one with the cracked backplate, the one that fits, is (or more correctly was) a 10V
The other, the one that doesnt fit, (the original engine from the car) a 10MA
That is not to say that either of them have the backplates they were born with and you would not have noticed the difference on re-assembly unless you changed the oil pump for a 'spade' drive type to fit MG Metro cam. It could be that I have a backplate from a 10CC engine but both the pump covers are identical. looks more like horrendeously bad quality control.

[PSL184]

I seem to remember that we have been here before and had decided that the backplate was dependant on what type of pump was fitted - or am I over simplifying.....

[bmcecosse]

The oil pump has NEVER been moved in relation to the crank! Over the years there have been various different oil pumps - but they are always in the same place - just some stick out a bit more than others. I really don't think the backplate is 'cast iron' - surely just a piece of flat steel - low quality, admittedly!

[billlobban]

When you think about it logically if they moved the pump they would have had to move the cam which would mean a completely different block
My money is on very poor quality control.
Interested to find out if the backplate is indeed cast or low grade steel. If its steel I'll have a go at MIG welding it with pre and post weld heat treatment via the oven (wifes away so what she dont know )

[bmcecosse]

I think you would do better with 'stick welding' Bill! But no harm trying the MIG - just do short runs - and keep turning it over and doing a bit on the other side.

[billlobban]

Dont have the facility Roy so its MIG or nothing. Got a scrap engine with a broken backplate might just practice on that first. Might be a problem with penetration though as I've only got a horrible Migmate 130 turbo which is OK for chassis tin but might not cope very well on a piece of 'steel' plate

[bmcecosse]

Stick welders are dead cheap - and cheap to run too - and good fun ! Handy to have.......

[IslipMinor]

I don't think any of the backplates are cast iron? I would grind out a 'V' all the way down the crack line, on both sides of the plates. Ideally deep enough to go halfway in on each side. Turn the welder up to its maximum current setting and use a gas containing Argon, pure CO2 will very likely produce a porous, poor quality weld, and weld a maximum of 2" on each side at a time, and let it cool down, before repeating the process. Any more and there is a real risk that the plate will distort and become useless.

You might need to 'weave' the wire slightly from side to side to fill the width of the 'V', which is fine, and should produce a good flat weld. The engine side of the plate will need dressing flat to mate with the gasket, but I would leave the flywheel side 'as welded', unless it is by a bolt hole, where it will need local dressing.

When you get near the bolt holes, weld straight across on one side, and BEFORE welding the other, drill back through the hole, using the unwelded side as a location. Repeat for the second side.

Finally, check the glass in your mask, quite often they are fitted with a No. 11 as standard, but unless you have unusually sensitive eyes, I would use No. 10, which will allow you to see what you are doing much better. I assume you know with MIG, you 'push' weld, not 'pull'? This also has the advantage of allowing you to see where you are going! And of course wear long sleeves to avoid 'sunburn' on your arms!

[linearaudio]

No way is the backplate cast. It would be impossible to sensibly cast that thickness over that area, and would have needed trapanning on both sides to get a flat even thickness, then would have been far, far too weak for the job!!
Don't even try with your SIP spit-welder!! Not a chance it will weld that thickness on that size- the heat dissipation will fry the transformer trying to cope. Go to your local blacksmith/ car repairer/ scrappy on a happy warm day, just after lunch, and someone will run a stick along there in 2 minutes. Worth £10 even to someone North of the wall
Do what all advise and drill/ vee first of all, so you are just asking for a weld run. Short bursts on alternate sides, it won't buckle seriously enough to worry for it's application. Quite possibly the "wrong" backplate was the result of an error in the original drawings or the interpretation of them on the shop floor, but as has been commented, with the pump as used at that time, it would not have been seen as warranting being scrapped as it was fit for purpose!

[Alec]

Hello Bill,

I would bet that it is cast iron as steel is much less likely to crack in that sort of application. If it is cast you won't be able to weld it with a MIG, I have read that you can use a MIG for brazing though?
If it is steel then welding is relatively easy.

Alec

[IslipMinor]

Don't even try with your SIP spit-welder!! Not a chance it will weld that thickness on that size

Sorry, I disagree. I have had a SIP 130A MIG welder for 12+ years, and have used it for all manner of tasks, and would not hesitate to use it on this job. The 948/1098 backplate, properly prepared, is well within a 130A MIG welder's ability to cope with for the application required, which is not exactly a high stress structural requirement.

Good preparation is always the key and 130A is good for 3-4mm plate, and the 948/1098 backplate is 1/4" (6mm) thick from memory? By preparing it from both sides, the weld required is effectively 1/8" or 3mm.

[billlobban]

Thanks for all the advice guys - I'm going to give it a go - need some Argon mix first. I was thinking of pre and post heating.
Stick it in the oven weld one side in segments and repeat for the other side. Then stick it back in the oven to the same temperature and gradually cool it down over a couple of hours