Hey all,

I'm not too far off rebuilding my NC30 race engine and am wondering if anyone has any tips advice or pitfalls to look out for with these V4's. I have read the Haynes and the Honda manuals, but I am looking for anyones hands-on experience.

Cheers
Luke

Also, I'm after some advice on main bearing clearances. Starting with the bearing based on colour codes in the Haynes manual (4x Green), I have measured mine and get a reading of 0.04mm with a micrometer. Then I double-checked with some plastigauge and the reading came out at a shave under 0.05mm (next lowest mark on the chart is 0.038mm). All good and at least they agree (though I wish my micrometer went to 0.001 accuracy!)

However, the Haynes manual gives a clearance of between 0.025 - 0.049mm with a service limit of 0.07mm. So I'm well under the service limit, but am pretty much hitting the base upper limit.

Would people generally run with this or would they swap out the bearings for the slightly thicker ones? (brown, I believe) to bring the clearance down by 0.016mm to around ~0.033mm?

I'm no expert, but I would have thought increased bearing clearances would give more power but less engine longevity?

Considering that it's still within the service limits:

- How much mileage do you want from it?
- Do you plan on opening it up again in the future?
- Would it be realistic to expect other engine wear (requiring a rebuild) before your crank bearings are out of tolerance?

I'm interested also in hearing what someone with engine building experience has to say about this.

I was going to start a thread along these lines as im soon to be stripping down a motor for a full refresh so keep it going, any info will be helpfull. Are you doing any flowing to the crankcases/head, any lightening or balancing?

I would get a set of brown shells and see where they gauge at.

Cammo wrote:I'm no expert, but I would have thought increased bearing clearances would give more power but less engine longevity?

Considering that it's still within the service limits:

- How much mileage do you want from it?
- Do you plan on opening it up again in the future?
- Would it be realistic to expect other engine wear (requiring a rebuild) before your crank bearings are out of tolerance?

I'm interested also in hearing what someone with engine building experience has to say about this.

Not sure how much to expect out of an engine. It is a race build, but I would hope to get a couple of seasons before having to open it up again! I guess this is the bottom line- keep an eye on it! The shells/journal won't wear overnight , so as long as it gets a check/refresh every X year(s) then it would probably be ok. They are in spec right now.

Other reason for asking, is I have been searching for information about what rules builders follow when blueprinting engines regarding bearing clearances. Information is sketchy (and with a lot of the internet, to be taken with a pinch of salt) but I'm curious if it is recommended to get as close to the min. tolerance or the max. tolerance and what is the trade-off of going either way! One guy from Christchurch who built a couple of NC30 engines back in the 90s found that out of the box, both did bottom ends under racing. He said that he found the oil holes on the crank needed to be radiused and thinner bearing shells as the clearance recommended was too tight. This is why I'm curious to hear from other engine builders as well!

Drunkn Munky wrote:I was going to start a thread along these lines as im soon to be stripping down a motor for a full refresh so keep it going, any info will be helpfull. Are you doing any flowing to the crankcases/head, any lightening or balancing?

I have had the crank balanced but only a small amount of material removed (~10g from each end). Pistons and rods were also matched prior to balancing. The heads have been skimmed 0.5mm and I have done some mild porting to the intakes (seat->bowl blending, intake rubber matching and casting removal). Also fitting NC35 pistons, but still need to do some volume calculations as to whether they increase comp or not! They are definitely lighter as they use a shorter wrist pin to the NC30. Last thing on the list is to send the internals off to the US for cryo/REM finishing (hopefully off on Monday) which Mike N highly recommends. Then rebuild.

Thats pretty much what ive got in mind for my rebuild, how much of that did you do yourself?

Pretty sure its just the NC29's that benefit from higher comp by fitting 35 pistons although as you say they are lighter than the 30 pistons. What parts are you having REM'd?

How did your shims go from that template?

My fabricator mate is on his honeymoon so i'm yet to have it done.

I'm just about to install my rebuilt engine.
When I split the cases and inspected the shells,they looked like new,only a couple of places with a little shine on them,so I just replaced like with like.
Looking forward to starting her up and finding out if I forgot anything

Drunkn Munky wrote:Thats pretty much what ive got in mind for my rebuild, how much of that did you do yourself?

Pretty sure its just the NC29's that benefit from higher comp by fitting 35 pistons although as you say they are lighter than the 30 pistons. What parts are you having REM'd?

That's what Cammo said. When I get it all back from the US I'll see if I can come up with some definitive numbers. Even the pistons weigh virtually the same, but it's the skirt redesign that allows a shorter pin that saves weight.

Most of the heavy work has been done by an engine reconditioner in town (balancing, skimming, re-honing etc.). The porting I have done myself and also the deburring edges i!n/on the block.

Biggest thing I have found with this blueprint is the amount of measuring/checking and cleaning that I have done! It is nice though that when it goes back together, I'll know that every part is spot on.

As from REM/cyro, I'm sending virtually everything inside the engine that moves. I'll post some pics and a list to my racebike thread when I get it back!

Lane wrote:How did your shims go from that template?

My fabricator mate is on his honeymoon so i'm yet to have it done.

I have had the cam tower shims cut from the original and they are all good. I had a place in Oz make up the gear tower and cover bolt shims, but they were crap, so got them re-made at the same place as the first batch. Should hopefully be here next week