Anyone Ever Rebored/overbored A 5/6Th Gen

[CandyRedRC46]

If you look on the Honda prelude and s2000 forums there is tons of info on frm and mmc liners with regard to forged pistons.

http://www.preludezone.com/naturally-aspirated/25642-honda-tuning-lets-talk-frm.html

But yeah maybe you're right and it's more about material make up than the coating. I'm not sure. I just wanted to make sure that you had looked into it first :)

[Mohawk]

Yeah but you re talking about "after market" which are NORMALLY raw alloy finish for use in Iron/Steel liners. The real issue is that Iron/Steel liner expand at a slower rate & not as much as an MMC or Alloy with Nikasil, so the clearances between the fresh bore & piston are critical. Thus the piston has to be designed to work with an MMC or Alloy-Nikasil liner, this means its cold edge clearances will be at perfect tolerance when the engine reaches normal operating temp.

If designed for MMC then they only require the skirts coating with solid lube compounds to protect them during run in. I have a few 954ex race bike pistons & 929 road bike ones that have the lube compound worn off & NO sign of pickup on the skirts. None had any compound between the ring lands & if the piston is matched to the bore correctly, they will not pickup or seize.

That is the basic problem, plus a bunch of idiots on car forums that don't do any research & then spout rubbish as fact :) But that's car modders the world over.

[HighSideNZ]

Also, just to add 2 cents worth, the early Preludes used the first gen MMC liners and they had lots of issue with them.

As far as I understand, what we are playing with is the later gen MMC and all the bugs have been ironed out.

I agree with Mohawk, as far as I can see the CBR range ALL use MMC with the forged pistons.

The VFR uses cast pistons just for a cost saving situauion.

Mohawk, I couldn't get cranking pressures on the motor before I stripped it as it was in no state to be turned over so it will be a surprise when i fire it up I suppose.

I'm running the same cam timing as yours. I was going to go with the standard RC45, but after you posted your specs and outlined what you had achieved, I thought yours would be the way to go.

Time will tell, once I've got the cams back.

I'm hoping to strip the pistons out tonight and finish the squish areas off with 1mm clearance from the top of the crowns. This will bring them inline with the standard pistons.

When I linished the pistons down I ended up putting a pin in an old piston and measuring from the underside of the pin to the crown and then doing the same on the 929 pistons.

All of them now measure the same as standard. 31.77mm

If I can get all the squish areas the same I can then burette the combustion chambers and match them all up.

That should be the end of the piston work until I can check valve to piston clearances.

Phil

[HighSideNZ]

Question for you Mohawk

The shop doing my cams has had to remove the welsh plugs from the ends of the cams.

I take it your guys had to do the same thing?

What did you use to replace the plugs?

Cheers

Phil

[Mohawk]

Hi Phil, They were removed and new ones fitted I believe, I had mine done a a bike cam center, Piper Cams, so they have spares for this, they are a tight friction press fit, the oil pressure in the cams is not high.

[HighSideNZ]

Thanks for that.

Don't have the options down here in NZ.

I was thinking of getting some aluminium bungs turned up and press fit & loctite them in.

Did that with my VF750 back in the 80's

[Mohawk]

Yeah that should work, alloy will expand quicker with heat so should stay the course.

Did you strip the anti-lash gears off before sending the cams to be ground ? I did, just as well as they would collect grind, pain in the butt to put back on.

[HighSideNZ]

That is what I was thinking with aluminium. higher CoE so should stay in place, especially with some loctitie bearing mount on them.

No I left mine on but I will need to strip them off to clean.

How much of a pain in the butt are you talking?

Also, are the actual drive gears splined on to the cams?

I take it you are pretty much fixed as far as degreeing the cams goes.

What they grind is what you get!

Got the piston crowns completed last night. It removed another 1g in mass so the bare piston is down to 175.5/176.0 type mass now.

With the 929 pins being 1g heavier and the ring set being about 1g heavier as well, the total mass is now pretty much exactly what the standard VFR assemblies were.

Balance factor should not be altered at all, and with me getting the rods as close as I have it should be nice and smooth.

[Mohawk]

They are a pain to re-assemble because the pin the locates the spring keeps shooting out just as it's about to snick home. Make sure you do it somewhere tidy so you can find the pin.

The gears are standard press fit, so you can adjust them, but it's a real pain & true accuracy is very hard to get, but it can be done. You are obviously limited in the number of attempts !

[HighSideNZ]

Thanks for that.

Shame they didn't spline them with say 1 more tooth in the spline compared to the number of teeth on the gear.

You could then use it like a vernier. May not be degree by degree, but a lot easier than pressing them off and back on

[HighSideNZ]

Well progress is still happening.

Just sent all the cases off to be vapour blasted so they should come back looking like new.

Still waiting on the cams so can't do anything else until I've got them and the cases, plus bearing and new rod bolts etc.

Next job is to clean up the throttle bodies and fit the R6 trumpets to the air box bottom.

I'll post again once I've got some bits and start the assembly process.

Cheers

Phil

[Mohawk]

Keep at it Phil, we are all rooting for this ;)

[Rush2112]

^^^^^ + 1/0

[HighSideNZ]

Well just heard from the cam grinders.

They are now going to have to build up and regrind the centre journals on the cams as they have distorted during the refacing process.

Another cost I didn't want or expect!

It probably would have been cheaper and quicker to send the cams to Pipers in the UK than for these people to stuff around with them.

To say I'm annoyed is an understatement.

[gll429]

Well just heard from the cam grinders.

They are now going to have to build up and regrind the centre journals on the cams as they have distorted during the refacing process.

Another cost I didn't want or expect!

It probably would have been cheaper and quicker to send the cams to Pipers in the UK than for these people to stuff around with them.

To say I'm annoyed is an understatement.

why are YOU paying more to fix their mistake??? they screwed up.. THEY fix it end of story!!

if they dont.. remind them the world is a VERY SMALL PLACE now thanks to the internet!

say you dont want to post bad reviews all over links that they have..

[Mohawk]

Holy crapola, they must have screwed it up big time. Hope they sort it out ASAP. We feel for you :(

[HighSideNZ]

Hey, NZ is a small country and suppliers are hard to find.

I've already had to pay a 50% deposit for the cam reprofile, so if I didn't go them halves on their f$#k up they would have sent the cams back as is.

I feel it is the best of a bad situation.

All I want to do is get my gear back in a usable state.

I'll have my revenge after the fact. I know enough people in the bike racing scene so a few choice works in the right ears will do what I want.

[Dutchy]

Payback is a bitch..... :-)

[HighSideNZ]

Hi guys

Just got back in to the build and have burretted the chambers and an assembled piston/head assembly.

The front head measures 14.4cc and 14.3cc for the chambers

The back head are both 14.0cc

The assembled unit measures 16.0cc on #1 (14.0cc chamber)

From my calcs, this is going really high in CR with a static CR of 13.89:1

This would give me a dynamic CR of 12.39:1 (inlet closes 45 deg ABDC)

I feel I'm going to have to open the chambers up to say 15.5cc (this would be a measured 17.5cc assembled)

With this size I'll end up with a static of 12.78:1 and a dynamic of 11.41:1

Anyone got any thoughts? Trying to keep the bike trackable on the road.

Cheers

Phil

[HighSideNZ]

Further to the above.

I cannot open the chambers up to 15.5cc and after balancing all chambers to 14.4cc it looks like I'm stuck with that.

From my calcs, I get the following:

Chamber volume = 14.4cc

Gasket volume = 3.44cc

Piston volume (including gasket) = 2.2cc (piston has a negative impact as it is higher than crankcase surface)

So with a swept volume of 206.4cc (74mm bore x 48mm stroke)

Working chamber volume = 16.6cc

Static CR = 13.4:1

Dynamic CR (45deg ABDC inlet close) = 11.98:1

Looks like it will need to run on 98 octane, but it should make some power. Here's hoping. Maybe 95 at a pinch.

Working back from what I've measured today, the standard CR for a Gen5/6 VFR doesn't seem correct at 11.6:1, unless they are talking dynamic and even then it is low.

From my calcs, the standard static CR is 12.77:1 based on a 14.4cc chamber. Dynamic would be 11.96:1 (35deg ABDC close)

So from this, I'd have to say I'm in the ball park.

[trjerm]

are you going to dyno it when you get it running

[Rush2112]

Further to the above.

I cannot open the chambers up to 15.5cc and after balancing all chambers to 14.4cc it looks like I'm stuck with that.

From my calcs, I get the following:

Chamber volume = 14.4cc

Gasket volume = 3.44cc

Piston volume (including gasket) = 2.2cc (piston has a negative impact as it is higher than crankcase surface)

So with a swept volume of 206.4cc (74mm bore x 48mm stroke)

Working chamber volume = 16.6cc

Static CR = 13.4:1

Dynamic CR (45deg ABDC inlet close) = 11.98:1

Looks like it will need to run on 98 octane, but it should make some power. Here's hoping. Maybe 95 at a pinch.

Working back from what I've measured today, the standard CR for a Gen5/6 VFR doesn't seem correct at 11.6:1, unless they are talking dynamic and even then it is low.

From my calcs, the standard static CR is 12.77:1 based on a 14.4cc chamber. Dynamic would be 11.96:1 (35deg ABDC close)

So from this, I'd have to say I'm in the ball park.

Dude,

Glad to hear you are making progress. I'm traveling for work so I don't have my spreadsheets to confirm the calcs... I do know that measured working combustion chamber volume is like 1.8 cc less than calculated.

[Dutchy]

Pictures?!?!

[Mohawk]

Hi Phil, Hmmm interesting. I calculated std at 18.4cc assuming the 11.6-1 claimed was true. Dynamic was 10.98 iirc.

I'd go with the principle that you know it worked regardless before, so you know how much you have added, so can do some basic calculations.

Remember that cam timing is NOT the same both ways, that's why I asked if you had done a cylinder pressure test. The 235 degrees is at 1mm lift, so you still lose some stroke before the cylinder is sealed, except at peak torque where you would expect a higher compression ratio, as cylinder filling is generally better than 100% at that point ! Likewise engine load has a serious impact on how the compression ratio reacts, as in high load high gear can produce pinking, but a lower gear freer revving engine wouldn't ! Should be good to go.

[HighSideNZ]

Hi Mohawk

Yes, I did the same, taking the advertised CR at 11.6 as being correct. Extrapolating that out with the increased swept volume I got 11.9:1 static CR.

But, I'd have to say that the chamber volumes I've measured are as I stated, 14.4cc. Did the measurement many times as I balanced out the 4 chambers.

Using these:

Chamber volume

Burette

Spark plug hole adaptor (5.8cc volume)

The standard head gasket thickness is 0.8mm which gives a volume at 72mm of 3.26cc and at 74mm of 3.44cc

When I measured the installed chamber volume, I sealed the piston in the bore with grease, dialed the piston to TDC and greased both sides of the old head gasket, then screwed the head down.

Then I fitted the spark plug adaptor above. I again sealed the thread with grease.

With the head leveled in both directions, I filled the chamber via the burette to the top of the adaptor.

The volume measured was 22.4cc less 5.8cc for the adaptor left me with 16.6cc for the working chamber.

So, static CR is:

(Swept volume + working chamber volume) / working chamber volume. (206.4 + 16.6) / 16.6 = 13.43:1

I've used a couple of online dynamic CR calculators and both give the same results at 11.98:1

Does this all look valid from an outsiders point of view?

Cheers

Phil