NitroStar S25, 1st start-up after strip & clean.

[Gazzman]

So this is one of the engines I got with the 2 Savages I purchased over Christmas. It's an HPI NitroStar S25 and had been sitting unused for around 2 years so I decided to strip it out and have a look inside. The engine was pretty gummed up with old fuel but everything looked good. Cleaned every part, lubbed it all up and re-assembled it. Did put a new pressure pin & spring in it while was apart. The compression was good but is now even better. The carb was also stripped and cleaned and the tune on it seems not to bad for the 1st start-up, will need fine tuning when I get it out for a run. but there doesn't seem to be any leaks from the backplate or front bearing which is good news.
And before anyone asks why the rear right wheel isn't spinning well that's because I am still missing a drive shaft for it.

 

[guinnessdublin]

Good job Gazzman looks & sounds fine to me!

 

[Gazzman]

Yes for a shed that was going to be broken for spares must say come together pretty good. As for the engine it has very good pinch and does look like it was maintained well by the previous owner. Going to see if I can find a replacement cooling head for it as it's pretty badly scrapped on the top. Will probably replace the shell to.

 

[Alien]

Dobra robota. Mam taki nowy silnik na części, brakuje tylko łożysk. Muszę to uruchomić

 

[Gazzman]

Dobra robota. Mam taki nowy silnik na części, brakuje tylko łożysk. Muszę to uruchomić

Well before you get the bearing for the crankcase, be sure to check the crank diameter for the inner(rear) bearing, there are 2 sizes, 1 is 12mm & 1 is 13mm ID. the old style S25 engine, the one with the circular cooling fins on the case used a 12mm ID bearing were as the F4.1 which people still refer to as the S25 uses a 13mm ID one. Check out the post from Owenmax below.
https://www.hpisavageforum.com/threads/need-help-s25-engine-bearings.20477/

 

[guinnessdublin]

Could not of said better myself Alien.

 

[Alien]

Well before you get the bearing for the crankcase, be sure to check the crank diameter for the inner(rear) bearing, there are 2 sizes, 1 is 12mm & 1 is 13mm ID. the old style S25 engine, the one with the circular cooling fins on the case used a 12mm ID bearing were as the F4.1 which people still refer to as the S25 uses a 13mm ID one. Check out the post from Owenmax below.
https://www.hpisavageforum.com/threads/need-help-s25-engine-bearings.20477/

If I remember correctly because I have already measured and searched, I have 13mm

 

[Gazzman]

Well took this truck out for a play today, managed to get it dirty and managed to break it, not to bad for a days work, LOL. Looks like I have stripped both diffs, know they were only 13/43t but reckon they must still have the plastic diff case. Truck was running really good, only took it out to test the new radio gear and life battery hump which both worked great. Leaned the mixture up a bit as was only getting to 185-190°F, it starting running even better and was really flying, wheelieing all over the place which for a stock S25 I was pretty happy with then noticed it was only driving the front wheels, should have stop then but oh no had to keep ragging it and next thing you know no drive. Oh well time to take it apart and have a look at the damage.
Will upload photos of damaged parts later, but reckon the cases have let go.

 

[Gazzman]

Well have stripped both diffs out and dismantled the front one. And as expected the chocolate plastic case has let go. One of the 2 cross pins holding the spider gears in place has eaten its way into the case causing the spider gears to skip of the 2 larger gears and as these are made of chocolate to has shagged them. Oh well no point in replacing the parts as alloy cases are £12.50ea & the gear set is same, times that by 2 and is cheaper to just 2 sets of 9/29 diffs off AliExpress @£20ea.

Anyway here the damaged parts and the lesson learnt here is, even if it's just a S25 mill it's worth getting alloy diff cases.

See the left gear has bent the tips of the teeth over, got away with the other as only 1 pin cut into the case.

The 4 spider gears didn't come off to bad and can be reused at a push.

 

[Alien]

I had the same thing on plastic cases during testing. Aluminum housings are the basis.

 

[Gazzman]

I had the same thing on plastic cases during testing. Aluminum housings are the basis.

To true my friend, have 2/29t bulletproof diffs in 11 of my 13 trucks, looks like now it will be 12. This truck was make from parts left over in my parts bin & that's why it ended up with good old plastic ones.

 

[Alien]

I understand you well bro. I have a container of parts like this myself and I'm thinking about assembling another one.

 

[Gazzman]

Well have taken the rear diff apart and this one didn't even have the spider conversion in it, only had 2 planetary gears like the original Savage 21, didn't think any of these diff would still be around. No wonder it destroyed itself, this diff failed before the front one did. And would explain why it took out the front one as all the load was then on the front. If I had stop the truck when I noticed this one fail could have probably saved the other.

 

[Alien]

That's possible

 

[Gazzman]

That's possible

Sure is, anyway glad they failed now when just out testing than in the summer when out for a proper run. This time of year only take them out really to keep the mills clean & fresh inside, good to run them regularly stops them gumming up. Mostly this time of the year I run them in doors on the kitchen worktop.
Yep I live in a flat & yep my neighbours love me.

 

[Gazzman]

Well have managed to salving one diff, found a set of planetary & a spare diff case in my box of bits, so things looking up.

 

[Alien]

Jasne, w każdym razie cieszę się, że zawiedli teraz, kiedy tylko testowali, niż latem, kiedy byli na właściwym biegu. O tej porze roku wyjmuj je tylko po to, aby młyny były czyste i świeże w środku, dobre regularne uruchamianie zapobiega ich zaklejaniu się. Przeważnie o tej porze roku prowadzę je w drzwiach na kuchennym blacie.
Tak, mieszkam w bloku i tak, moi sąsiedzi mnie kochają.

 

[Gazzman]

So bit the bullet and have ordered 2 complete new diff from AliExpress for a savage XL Flux, will need to switch over the output cups & change the crownwheels from 29 to 43t but works out alot cheaper than repairing these stock S25 diffs, plus no one in the UK has alloy diff cases in stock only downside is that I gotta wait 2 weeks for delivery. So one truck laided up in the shop till then but 12 more to break in the meantime.

 

[Alien]

I ordered diffs from Ali myself and they are good. You have to wait your time but that's such a small minus.

 

[Gazzman]

Yes I have had 5 pairs of diffs now from AliExpress and are working good. This set will make number 6. Buy quite alot of Savage parts from AliExpress. Works out alot cheaper and true you do have to wait abit but try to make sure I but my parts from sellers that offer the 15 day on time guarantee. Everything I have bought using that service had arrived in 2 weeks except one item and that down to the UK postal strike, it arrived in my country in 6 days but took good old Royal Mail another 12 days to deliver it. Recently had an order delivered by DPD from a UK seller and it took them 12 days to deliver.

 

[Gazzman]

So the new diffs arrived yesterday from AliExpress, not to bad on the delivery time as only order them on the 16th of Feb. Switched over the diff cups & Crown wheels last night. Changed over to easy access bulkheads while I was at it and this morning put it all back together. If it's dry tomorrow will get it out and see if I can break something else..
One thing I did find out from this was that the 43t & the 29t Crown wheels have a different size bearing with the 29t using a 16x8x5mm and the 43t using a 16x10x5mm which I found strange.

 

[Savage59]

So the new diffs arrived yesterday from AliExpress, not to bad on the delivery time as only order them on the 16th of Feb. Switched over the diff cups & Crown wheels last night. Changed over to easy access bulkheads while I was at it and this morning put it all back together. If it's dry tomorrow will get it out and see if I can break something else..
One thing I did find out from this was that the 43t & the 29t Crown wheels have a different size bearing with the 29t using a 16x8x5mm and the 43t using a 16x10x5mm which I found strange.

So, the easy access bulk heads fit the older truck's, nice.

 

[guinnessdublin]

So, the easy access bulk heads fit the older truck's, nice.

Not quite, you need X shock towers & bumper stop arms also!

 

[guinnessdublin]

So the new diffs arrived yesterday from AliExpress, not to bad on the delivery time as only order them on the 16th of Feb. Switched over the diff cups & Crown wheels last night. Changed over to easy access bulkheads while I was at it and this morning put it all back together. If it's dry tomorrow will get it out and see if I can break something else..
One thing I did find out from this was that the 43t & the 29t Crown wheels have a different size bearing with the 29t using a 16x8x5mm and the 43t using a 16x10x5mm which I found strange.

So was the bearing size change when the X version was released Gazzman?

 

[Gazzman]

So was the bearing size change when the X version was released Gazzman?

Must have been when they changed to the 9/29t diffs which I think was when the X came out. The strange thing is, they only changed to one on the crown wheel the one on the casing is the same for the plastic and metal one.