Bimota Forum

[brian]

Thanks for the update Bud. The new engine's looking great mate.

Yeah, i'm very interested to hear any updates on your yb8 and your racing in general. What part of January is the Island Classic held? I'm going to try to get down for it next year.
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'99 DB4 #104, '96 SB6 #1165, '94 DB2 J #652, '99 DB4 #088, '08 VTX1800, '93 ZXR750R M1, '95 ZXR750, '95 ZXR750 Race Bike, '94 CBR400rr NC29 Race Bike, '94 CB250, '49 BSA C10 250, '61 BSA A10 650, '89 ZXR750, '91 Ducati 851

[bloodnut]

Hey Bud, how are you getting on with the rebuild? Did you use an exup or thunderace motor?

[Bud977]

Hi Bloodnut, I've just started re-assembling the motor after getting back from the Australian Historic Championships at Lakeside in Queensland. I was pretty pleased to get 3rd on my TZ250A in both the Period 6 250 and Period 6 500 classes.

I've been mucking around trying to get the right shells for the main bearings. The Exup FZR1000 uses 3GM prefix shells for the centre bearing and 2GH prefix for the other 4 locations. I stuffed up and ordered all 3GM bearings.

So, I ordered the rights 2GH bearings (so I thought) and ended up with a 2nd set of 3GM bearings. Stupid me I thought. How did I stuff that up? I better order a 3rd set and get it right this time.

So I went to the bike shop and ordered the 2GH shells, and the parts guy tells me they have been superceded by the 3GM bearings! So I had the right ones all along.

It's odd that the YZF750 motor has always used only 3GM shells. The only difference is that the 3GM has a larger centre hole which I guess increases the oil flow to the main crank journals and reduces oil pressure.

As I've taken out the starter clutch, generator and starter motor, there are a few holes that require plugging. Some are to keep the oil in the motor, others are to maintain oil pressure. I'm making them up now.

There certainly are a lot of parts in these 4 strokes. I'm a simple two stroke man. I can see it's going to take me a while to get this motor back together.

[who]

Hi bud, the bearing shell of the mains and big ends remained the same throughout the series. The colour coding changed a little I believe between say the exup, and the thunderace. Forget about the crank and big end compatibility-sizing codes, the only way to do it is with plastigauge. Most of the time the rod markings are gone, but the bearing colour is quite often still visible on the side of the shell.
If you are using oem rods, have them resized and shot peened... after you have balanced them. (recheck afterwards) You weigh the bottoms separate to the tops. In the end you will end up with pretty good rods if every thing is weight even and in good condition.

The rod in your engine was an odd occurrence, especially if you were banging around at oem limit rpms. Make sure all the galleries are clear, and don't spend any time on the rear wheel (starvation) Cheers.

[Bud977]

I've been busy racing and dirt bike riding lately, but I've managed to get back to assembling the motor.

The bottom end is mostly back together. I'm waiting for a couple of bits from Yamaha to plug up the internal oil gallery and starter motor hole.



The crank is a standard FZR one. Sadly I destroyed the lightened crank that was in there before. The lightened one was 5kg lighter than standard.



All new bearing shells have been fitted, the 6 speed YZF750 gearbox is in.

I decided to take out the generator and starter gear as it weighs over 10kg. The race manual recommends that you remove the starter clutch bearing so that it doesn't fall out when the motor heats up. I didn't have a blind bearing puller so I used a dynabolt and a bit of heat to get it out.



The new Wiseco pistons are on. These are 2mm overbore giving 1040cc capacity.



The cylinders have been cleaned and honed and are ready to go back on.



So now I'm up to the head. These 4 stroke things have way too many parts!

[who]

Wow, shame the crank is toast. Any chance you could have the rod journal repaired?

[Bud977]

Not according to any engine builders I've spoken to unfortuneately.

I've got a lead on a company that (so I was told) build the journal up with chrome to reclaim it. I'll check it out in the future. For now, I'll run with a standard crank.

[who]

Standard crank won't have any influence on peak power output. The starter clutch removal is good for a 5 rwhp gain, as well as the obvious weight saving.

[brian]

Wow, 5kg is a huge weight saving on a bike Bud, let alone on 1 component. Looking at the pics, there's definitely a lot less material on the lightened crank.

Will you be ready for next season do you think?
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'99 DB4 #104, '96 SB6 #1165, '94 DB2 J #652, '99 DB4 #088, '08 VTX1800, '93 ZXR750R M1, '95 ZXR750, '95 ZXR750 Race Bike, '94 CBR400rr NC29 Race Bike, '94 CB250, '49 BSA C10 250, '61 BSA A10 650, '89 ZXR750, '91 Ducati 851

[Bud977]

I was excited to be taking 10+ kg off by taking off all that electrical equipment, but then I added 5kg back in with the crank. Oh well.

This is a grunt motor so the added crank mass will help coming out of cormers. The power drops off at 10,500 RPM so there is no point revving the crap out of it.

5 rwhp sounds like a bonus as well. I'll be curious to see what it comes with on the dyno.

I'm changing out the wheels, chain and sprockets as well. That should take off at least 5 kg as well.

This is my main project at the moment Brian. My plan is to be ready for the Island Classic again at the end of January. It seems like a lot of time, but it always seems to be a rush at the end, especially once you take out the Xmas break.

[who]

[brian]

[Bud977]

I've been busy getting the motor finished and learning a lot about setting up 4 stroke motors on the way.

First, I stripped the head down and cleaned it up ready for a refresh. During the blow up, the piston hit the 2 exhaust valves bending them slightly and smashing the shims and buckets. The plan was to give the head to my local engineering guru to check the remaining valves and seats for re-assembly by myself.

Here is the head stripped and cleaned ready for refurb. (Sorry about the focus) The two damaged valves hard to pull through as the end must have mushroomed when it got hit. The cracked bucket was hard to remove as well as it expanded into the bore. It wasn't pretty but I eventually got it out.



Before, reco, it was hard to tell the condition of the seats with all the carbon build up.



After a couple of weeks, the head is back. All cleaned up, seats cut,valves ground.



That's much better! This looks nice.



Now to start re-assembly of the head and set-up the shims. I want to get as much work on the motor done while it is on the bench as it is much easier. Actually, with the YB8 you can't even get the cam cover off with the motor in place so I HAVE to get this done now.

[brian]

Coming along nicely Bud. Great pics of the 5 valve head. Are you replacing the cams or reusing the originals?
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'99 DB4 #104, '96 SB6 #1165, '94 DB2 J #652, '99 DB4 #088, '08 VTX1800, '93 ZXR750R M1, '95 ZXR750, '95 ZXR750 Race Bike, '94 CBR400rr NC29 Race Bike, '94 CB250, '49 BSA C10 250, '61 BSA A10 650, '89 ZXR750, '91 Ducati 851

[Bud977]

I'm going to re-use the standard cams Brian.

The race cams for these bikes are not much different to standard. For example, in the YZF750 race kit you re-use the stock inlet cam and fit the race kit exhaust cam. The race kit cam has 0.1mm extra lift at the same 105° event. Then the kit recommends you run 0.1mm extra valve clearance, which negates the extra lift!

Actually, I was surprised my cams were standard. Everything else in my motor had been modified/upgraded by someone who knew what they were doing so there must have been a reason to keep the standard cams.