Lister sr3 ruined threads.

[Orakal]

Hi, ive stripped and rebuilt my lister as it has had water in pistons and ive replaced rings and honed heads, cleaned almost everything, changed gaskets and on the final straight ive been tripped up by dodgy threaded holes for the cam cover.

I think theres 9 bolts and 4 are no good now as the bolt will push in and out and obviously wont clamp the gasket down.2 are in the same corner so have to be sorted plus id sooner do it correctly.

I measured the bolt with a tape as its all i had to hand and it seems to be a 6mm bolt but probably imperial.

Ive been and bought but not opened a set of taps and dies with a , 3,4,6 and 8 mm tap but if it is 6mm the next size of 8 looks scarily thick and the head of an m8 bolt is huge in comparison.

So does anyone know what size the bolts are holding in the crankcase cover and the camshaft cover and what the next available size to drill and retap are?

 

Id sooner ask before i attempt it, thanks.

[Guest User]

1/4" UNF ? .... (on page 5 of lister maual http://www.bluemoment.com/manuals/lister_man.pdf ) .... could you use Helicoils ?

[by'eck]

Helicoil may be an answer.

[Phil Ambrose]

Agree, helicoil insert is the way to go

Phil

[Orakal]

Dont i need a thread for a helicoil?

[bizzard]

Dont i need a thread for a helicoil?

Indeed you do. Helicoils can I think be bought separately but you will need the correct oversize drill bit to drill through and clear away the old remnants of thread, the correct size tap for a 1/4'' helicoil or 6mm metric to be wound into, and the insertion tool. You will need to buy the little kit for that size from a tool supplier which will contain the above and most importantly ''insructions'' Hellicoiling would be the best and neatest method.

[rrt2]

Dont i need a thread for a helicoil?

Drill out old thread with the supplied drill - retap with the new thread that takes the helicoil insert - put helicoil insert in.

You may well find with the number you have to do it will be cheaper to buy a Helicoil set of the size you need rather than get someone out to do it.

Quick look on ebay about £25 for all you need

[Orakal]

ok so im happy to go with a helicoil set, any tips on what size assuming it is 6mm can you go just to a 7?, or would it need to be 8 to clear the old thread out?, any chance of an ebay link??

[Orakal]

I have done helicoils before when we resized kitkat wafer plates at my old engineering jobs so i understand how they work, just need help on the sizing, dont wanna get it wrong.

[bizzard]

I have done helicoils before when we resized kitkat wafer plates at my old engineering jobs so i understand how they work, just need help on the sizing, dont wanna get it wrong.

With a Hellicoil you will be bringing the size back to the original size. The drill drills the hole slightly oversize and the hole then tapped with the supplied thread tap and then insertion of the hellicoil into this slightly oversize tapped thread brings the finished thread size back down to the original 1/4''UNF or 6MM whichever you want.

[Orakal]

So the original size is 1/4 unf then, im assuming its going to be easier to find 6mm bolts as i realised today theres a couple of larger ones so id rather get 6mm....so look for a kit to return me to an m6 hole...great thanks alot for the help.

[bizzard]

So the original size is 1/4 unf then, im assuming its going to be easier to find 6mm bolts as i realised today theres a couple of larger ones so id rather get 6mm....so look for a kit to return me to an m6 hole...great thanks alot for the help.

Yes if you can't get a Hellicoil kit for 1/4''UNF go for 6MM, but I'd mark the new 6mm bolt heads in some way ''paint them red or something'' for future reference, for you are bound to forget if you remove the cover in future which are UNF and which are metric and start screwing the wrong bolt into the wrong hole and strip the threads.

[Grace and Favour]

1/4UNF kit

[Orakal]

Yes if you can't get a Hellicoil kit for 1/4''UNF go for 6MM, but I'd mark the new 6mm bolt heads in some way ''paint them red or something'' for future reference, for you are bound to forget if you remove the cover in future which are UNF and which are metric and start screwing the wrong bolt into the wrong hole and strip the threads.

Good idea i will do.

1/4UNF kit

Thanks for that, i would go with the original 1/4 but noticed putting it back on 2 bolts are oversized already dueing to a previous bodge job so ill go with 6mm seeing as though they will be easier to source.

[bigste]

Some advice and info for you. In my time as an engineer I have repaired and replaced 100's of threads. At one time I was doing this full time. There are 2 main ways to replace a thread. More common in the UK is helicoil. These are a stainless steel insert resembling a compressed spring. In my opinion the far superior method is the Timesert. These are not wire type, they are a bush with a thread on the outside and your chosen thread on the inside. They are also glued in place. Timeserts are especially suited to open ended holes like spark plugs as they have a shoulder on the top to stop them going in too far. Try googling or ebaying Timeserts.

IMHO your case will be happy with helicoils as they are blind holes and not open. Both are easy enough to fit but a good tip is to use plenty of grease to catch the swarf.

[X Alan W]

ok so im happy to go with a helicoil set, any tips on what size assuming it is 6mm can you go just to a 7?, or would it need to be 8 to clear the old thread out?, any chance of an ebay link??

You would require a 1/4 UNF helicoil kit this will enable you to fit the Helicoil & then fit your original stud/bolt providing the stud threads are good failing to obtain 1/4 UNF kit, a 6MMkit would do the job, but you would have to replace the studs as the thead diameter size & thread pitch are different, would be best to try to keep the stud size & thread the original size.

Good idea i will do.

Thanks for that, i would go with the original 1/4 but noticed putting it back on 2 bolts are oversized already dueing to a previous bodge job so ill go with 6mm seeing as though they will be easier to source.

If 2 studs are oversize be aware that the original 1/4 bolts would be larger than 6mm so you may have a problem you may have to go larger to 8mm

[rrt2]

You can put a helicoil into a helicoil to bring the thread size back to the original.

I had this done recently, two stud holes had been opened up to 3/8 unc, the others were a very poor condition 5/16 unf thread.

The firm that did the helicoil said we can bring them back to 5/16 by putting the larger diameter helicoil in first followed by the correct 5/16 size.

[Timleech]

I think you'll find they were 1/4" UNC rather than UNF, though happy to be corrected if somebody knows for certain.

 

Tim

[Orakal]

Some advice and info for you. In my time as an engineer I have repaired and replaced 100's of threads. At one time I was doing this full time. There are 2 main ways to replace a thread. More common in the UK is helicoil. These are a stainless steel insert resembling a compressed spring. In my opinion the far superior method is the Timesert. These are not wire type, they are a bush with a thread on the outside and your chosen thread on the inside. They are also glued in place. Timeserts are especially suited to open ended holes like spark plugs as they have a shoulder on the top to stop them going in too far. Try googling or ebaying Timeserts.

IMHO your case will be happy with helicoils as they are blind holes and not open. Both are easy enough to fit but a good tip is to use plenty of grease to catch the swarf.

Thanks for the advice, i was going to try and find a cutting compound to catch most the swarf as i dont want it in the engine, we used to use trefolex 20 years ago but i have a large tub of grease so ill use that.

You would require a 1/4 UNF helicoil kit this will enable you to fit the Helicoil & then fit your original stud/bolt providing the stud threads are good failing to obtain 1/4 UNF kit, a 6MMkit would do the job, but you would have to replace the studs as the thead diameter size & thread pitch are different, would be best to try to keep the stud size & thread the original size.

If 2 studs are oversize be aware that the original 1/4 bolts would be larger than 6mm so you may have a problem you may have to go larger to 8mm

On re examining it would appear the thread size is the same but the pitch is different so im guessing the previous owner used a metric when losing them.

I think you'll find they were 1/4" UNC rather than UNF, though happy to be corrected if somebody knows for certain.

 

Tim

This is the exact reason why im going to metric, i dont understand all these different types, when i was an engineer at 17 in 1991 it was all metric but we had a whole storeroom of taps and dies from imperial times and although sad to lose the history of it i can see why it was done to move to a simplified standard thread size and.

[Timleech]

This is the exact reason why im going to metric, i dont understand all these different types, when i was an engineer at 17 in 1991 it was all metric but we had a whole storeroom of taps and dies from imperial times and although sad to lose the history of it i can see why it was done to move to a simplified standard thread size and.

 

There's a valid reason for it being a coarse rather than fine thread, in that coarse threads are stronger in soft or weak materials.

Even so, it's very common to see these particular threads stripped, as that door is something that will be removed many times during the life of an engine and it's very easy to overtighten the screws.

 

Tim

[BEngo]

Metric threads into cast iron or aluminium tend to give very poor performance, because the thread is too fine. The door comes off regularly which means the fine threads wear very fast.

 

Helicoil type solution at the original coarse thread is much the best way forward.

N

 

Beaten by Tim.

[Timleech]

Metric threads into cast iron or aluminium tend to give very poor performance, because the thread is too fine. The door comes off regularly which means the fine threads wear very fast.

 

Helicoil type solution at the original coarse thread is much the best way forward.

N

 

 

 

The helicoil route, done properly, will be stronger than the original, and really to be full strength needs to keep to the original thread.

 

Tim

[Orakal]

 

There's a valid reason for it being a coarse rather than fine thread, in that coarse threads are stronger in soft or weak materials.

Even so, it's very common to see these particular threads stripped, as that door is something that will be removed many times during the life of an engine and it's very easy to overtighten the screws.

 

Tim

I saw in the manual not to apply the same torques to items such as the door bolts for this very reason, and being aluminium threads strip much easier.

[Timleech]

I saw in the manual not to apply the same torques to items such as the door bolts for this very reason, and being aluminium threads strip much easier.

 

Not everybody reads the manual

 

If you're determined to go the metric route, then a better bet would be solid inserts. These have standard threads inside and out, but obviously need a substantially bigger drill and tap so you have to be sure there's enough meat there to work with.

 

Tim

[Orakal]

Managed to get the m6 stuff from machine mart and sort it, decided to do them all,

 

 

 

 

So that all went well, bled the fuel and when i came to start it, lol click, click, click in the relay so took the starter out and it was a little stiff and gunky so cleaned it all up and greased it a little and now its nice and free but still click click so im charging the battery and try again tomorrow.....

 

Thankyou to everyone who has advised me so far in all my questions and problems, your all so knowledgeable and really do give seriously good sound advice allowing folk like me with a little practical know how do many an expensive job themselves.