NWL – Project Concours Carmine Sprint

[tony g]

That variation on the pistons is terrible. I would expect modern forgings to be 1-2 g max. Check the boss for the gudgeon pin for extra metal
If going heavy piston- light rod , only use the small end weight for reference. Its no good if the rod is light at the big end to compensate for the piston being heavy. rotational/reciprocating

Tony

[James467]

That variation on the pistons is terrible. I would expect modern forgings to be 1-2 g max.

That's what I was thinking.

I'm not going heavy piston light rod, I want them all to be the same, it just feels better that way.

[Jon Tilson]

I agree....send no 3 back...

Jonners

[James467]

Thanks Jonners, my concern is that there is something wrong with the makeup of the piston which could cause problems in the future. I have emailed JP If I can't get a response from them I'll talk to Rimmers as the seller.

In the meantime I'm cracking on with the rods, update to follow.

[James467]

Evening all, it's time to balance some rods!

First of all, thanks to Mart for introducing me to this, it has been a really enjoyable and I have learnt something new at the same time. Rod's arent that cheap but are cheaper than pistons so if I balls it up then at least I can get a new one!

For those of you who don't know what I'm up to here, what I am doing is ensuring that both the rotating weights and reciprocating weights are the same. To do that I need to weigh the small end of each rod and remove material as necessary to ensure that they are all the same. To do this you need a rod balancing Jig. They arent easy to find in the UK, I have this one from Amazon.com http://amzn.com/B000A8J5OY when buying one of these you need to ensure that all of the joints have bearings in to reduce any friction. Friction will translate into inaccurate weight readings. You'll also need a good accurate set of scales that measure down to 0.1 grams. eBay is good for this, mine cost about £8 with some calibrating weights. I checked its accuracy when it arrived and it's bang on.

In terms of going about doing this, I basically followed what the guy does in this Youtube video https://www.youtube.com/watch?v=QLpiF0E0EJU and looked at Jeroens thread here viewtopic.php?f=4&t=28355 on where to remove material.

The first thing I did was to weigh each rod and establish which one was the lightest.



The trick here is to ensure everything lines up and the rod sits horizontal. I taped the jig to the scales to minimise the risk of me knocking it all out of alignment. It takes some practice but I was able to take the rod on and off and have about 0.1g a difference per 10 goes.



Number 1 was significantly lighter so I put that to one side and noted down the other weights, on average I needed to remove about 6 grams from each small end.

I ended up having to remove quite a lot of material from the small ends, almost as much as Jeroen in his build.



I used a combination of a grinder, flap disc and a belt sander to remove material.

Small ends done.



The big ends are a bit easier, as the small ends are all the same weight any difference in the total weight of the rod would just come from the big end now. So it's just a case of weighing everything and taking material from the cap to adjust as required.



Number 1



Number 2



Number 3



Number 4



As you can see with a few trips to the belt sander I managed to get the total weight of each rod to within 0.2g of each other.

Then just as a double check I weighed the small ends again to ensure that I had done them properly.

Number 1



Number 2



Number 3



Number 4



The small ends are all within 0.1g of each other. I was trying to get everything within 0.5g so with the accuracy of the scales I should be well within that so I'm very pleased with the result here, this did take me all afternoon though so don't think it's a 5 minute job!!

The oil feed hole needs the countersink opening up, I need to get a bit to do this other than that they are done.



Just need to sort out the pistons now.

[Mahesh]

Keep this up and you'll get job offers for building warp drives.

[GTS290N]

I used to be impressed with this thread.




Than I went to awestruck.





Now... speechless.

[Pippin]

Great job James. I take it you've decided to balance them but not lighten them, at least not as much as Jeroen did in his thread.

[James467]

Thanks everyone!

Yes, I'm just balancing everything. I'd like to have a 'well built' engine rather than something that's been heavily modified. I think that properly balancing the engine is one of those things that BL weren't able to do at a good enough level on the production line which is why they couldn't get reliably close to that 135hp mark.

Had an email from Peter at JP this morning.

'You can take metal from the pin bosses and from the inside of the pin.'

7g is a lot of material to remove especially as they are aluminum and I don't want to take too much off the pin. I also noticed that the total height of the pistons are different, the lighter one is about 1.5-2mm higher than the rest, the difference being the skirt length. I just wonder if I have a 'dud' set, Rimmers don't have them in stock so I think this is a situation that requires a call to the land down under!

Just to put things in perspective, from Rimmers they cost close to £600 with delivery so I don't think I'm being unreasonable to expect them to be a bit closer in weight for that price.

[GTS290N]

I would want nothing less than perfection for that money!

[SprintMWU773V]

These are cast pistons and not precision forged ones therefore they will vary by quite a bit. When I weighed up a set of JP or a set of custom made JE forged ones, the JE ones were actually cheaper coming in at under £400 from the USA. There's virtually no difference in the weight between my pistons.

[James467]

Yes they are cast, looking at them though I don't think I'll get 7g off of them!

Cambridge Motorsports are selling the JE forged set for £678.

[geeksteve]

Yes they are cast, looking at them though I don't think I'll get 7g off of them!

Add 7g to the others, duct tape some wheel weights on

Steve

[Pippin]

Yes they are cast, looking at them though I don't think I'll get 7g off of them!

Add 7g to the others, duct tape some wheel weights on

Steve

After all, that's what Triumph would have done!

[SprintMWU773V]

Yes they are cast, looking at them though I don't think I'll get 7g off of them!

Cambridge Motorsports are selling the JE forged set for £678.

Ouch. I bought mine direct from the factory and then picked them up as I was in the area at the time.