Jet 200 engine casing.

[Storkfoot]

I have just stripped a Jet 200 engine that has several issues with endplate studs, the endplate itself and, as you can see in the photo, the edge of the casing where it mates with the mag housing. I only mention that as you can see the issue with the edge in the photo below.

Anyway, on taking a couple of photographs when I had got the engine mounts out, I noticed that the casing has something I have never noticed before. You can just about see that there are two small protrusions on the casing where the engine mount sits. This appears to be a deliberate attempt to keep the mount away from being forced in too far. But they aren’t replicated on the drive side.

Does anyone know what they are for?

[Warkton Tornado No.1]

The mounts cannot be pressed in too far as the correct sized hole is not 'through' & has a marginally smaller diameter hole inboard to act as a stop. The overall width of the engine mount lugs is fairly nominal because the critical features are the stop faces just referred to.

The two lugs are likely as the result of the die casting process & would normally have been removed along with any other casting flash during the finishing process. Any casting of molten metal requires a means of somewhere in which to pour/inject & a route for air to escape. I had always thought that the two square blocks on the case underside - besides being machining datums- would have been where the molten alloy was forced in under light pressure but never really considered where the air should escape.

[Storkfoot]

…/-
The two lugs are likely as the result of the die casting process & would normally have been removed along with any other casting flash during the finishing process. Any casting of molten metal requires a means of somewhere in which to pour/inject & a route for air to escape. I had always thought that the two square blocks on the case underside - besides being machining datums- would have been where the molten alloy was forced in under light pressure but never really considered where the air should escape.

I’ll give you that one

I have just never noticed it before and I did once strip and rebuild a Lynx engine.

The casing will be off to the engineer’s shop next week. I am just waiting for a new endplate to arrive. The existing one has a large oval hole where someone has rather hamfistedly tried to fix a stripped thread. That has resulted in both dowel holes in the casing becoming oval too.

Has anyone ever used an oversized/stepped dowel pin? Just a thought at the moment

[Warkton Tornado No.1]

If the case is going to an engineering shop that has good inspection facilities, then they should be able to measure & record a good endplate hole centres by which to work to. In fact, if any OEM blueprints exist for either the endplates or cases, that would be extremely useful for the LCGB to have on record......

In any case (excuse the pun ) with the critical dimensions obtained, the engineering shop should be able to correct any misaligned/oversized holes by deeper drilling. Personally, my preference would be to fit hollow dowels/sleeves in the correct dowel positions to take OEM type 7 mm (check that!) dowels & Helicoil inserts for the M7 stud holes.

To answer your question, there is no issue with stepped dowels apart from my own reluctance to use stepped fastenings such as studs. Stepped studs as marketed by some have no certainty of correct strength, whereas OEM studs are of the correct quality &, of course, longer M7 studs intended for the cylinder inlet can often be utilised in place of the shorter endplate fixings. I have often done so with damaged cases as well as inserting M7 Helicoils in dire cases.

For the record, prior to obtaining M7 Helicoiling kit I tapped out some slightly baggy endplate stud holes with an M6 Helicoil tap (same pitch) & fitted Holokrome/Unbrako/GKN high tensile M6 SHCS's & it was fine. There is often some cynicism associated with Helicoils, but the fact is many manufacturers - Rolls-Royce included - fit them during manufacture to stressed alloy components.

I hope that information helps.....

Edit: Having just re-read your last post, the fact that you await a 'new endplate' concerns me, if it's anything like the majority of remade components. I'm surprised you haven't a selection of spare endplates (it doesn't need to be OEM Spanish, though they are as good as OEM Italian). I wouldn't trust the Indian endplates for accuracy. If you need an OEM Innocenti endplate, I'm certain I could spare one.....

[Storkfoot]

If the case is going to an engineering shop that has good inspection facilities, then they should be able to measure & record a good endplate hole centres by which to work to. In fact, if any OEM blueprints exist for either the endplates or cases, that would be extremely useful for the LCGB to have on record......

In any case (excuse the pun ) with the critical dimensions obtained, the engineering shop should be able to correct any misaligned/oversized holes by deeper drilling. Personally, my preference would be to fit hollow dowels/sleeves in the correct dowel positions to take OEM type 7 mm (check that!) dowels & Helicoil inserts for the M7 stud holes.

To answer your question, there is no issue with stepped dowels apart from my own reluctance to use stepped fastenings such as studs. Stepped studs as marketed by some have no certainty of correct strength, whereas OEM studs are of the correct quality &, of course, longer M7 studs intended for the cylinder inlet can often be utilised in place of the shorter endplate fixings. I have often done so with damaged cases as well as inserting M7 Helicoils in dire cases.

For the record, prior to obtaining M7 Helicoiling kit I tapped out some slightly baggy endplate stud holes with an M6 Helicoil tap (same pitch) & fitted Holokrome/Unbrako/GKN high tensile M6 SHCS's & it was fine. There is often some cynicism associated with Helicoils, but the fact is many manufacturers - Rolls-Royce included - fit them during manufacture to stressed alloy components.

I hope that information helps.....

Edit: Having just re-read your last post, the fact that you await a 'new endplate' concerns me, if it's anything like the majority of remade components. I'm surprised you haven't a selection of spare endplates (it doesn't need to be OEM Spanish, though they are as good as OEM Italian). I wouldn't trust the Indian endplates for accuracy. If you need an OEM Innocenti endplate, I'm certain I could spare one.....

Thanks for that. I’ll add that to the discussion when I take it down to the engineer.

The endplate has just turned up in the post. It is an old Spanish one of similar vintage. Given the state of the casing, I can’t tell whether it is a good match but I would think it should be okay for the engineer to work to.

Unfortunately, I only had spare GP endplates which I didn’t want to use but may well be useful in the future.

Thanks again.