TR500 replica build

[ChrisK]

Well, I've pulled the motor down and we definitely have a holed piston, as I feared.



The bore is looking a bit worse for wear but I am not sure yet if that is alloy deposit or actual scoring. I am going to etch it to see what happens when the alloy dissolves. Might end up being able to just hone it with any luck. These are only the shakedown barrels so if they are a total loss at this bore size, so be it. I could bore them out for the custom pistons I have for the new motor but I might as well just go to the multiports and be done with it if it's not a quick fix.



I think the piston may well be stuffed!



So what was the cause? We suspect we had an airleak on this side as the CHT was up to about 135 so it would have been running lean. When I split the crankcase, the centre bearing o rings disintegrated. This was a brand new Cruizin Image one. The challenge now will be to try to clean out all the bearings insitu to make sure there is no piston residue lurking in there as well as make new o rings in place to try to save having to tear down the crank.

We also scored a cracked head earlier in the day. Unusual in that we were only running standard compression and the head torquing was carefully done. The head gasket blew out completely but I'm not sure which was the chicken and which was the egg, I suspect the crack came first. Luckily I had some spares.



Oh, and just to prove we were there

[tz375]

That is one Looooooong drive. Only did it once and it took 3 days IIRC driving dawn til dusk.

Piston is a little bit stuffed. Try muriatic acid on the bore. It will dissolve all the alloy in seconds/minutes.

With the front end chatter, if it's a frame resonance issue it might be a pain to fix. Tow suggestions: Try more weight (yours) over the front end to change the ratio of sprung to unsprung weight and throw both disks away and fit one from Manta. It's the only semi floating disk that's approved as a replica of an RG500.

If that doesn't work try different forks that resonate at a different frequency and see if that odes the trick.

Looks good though..

[ChrisK]

thanks. Have you got a link to Manta, they don't seem to come up in a google search?

[Zunspec4]

Hi Chris,

My original engine, after running OK on the dyno, also holed a piston when I took it to it's first race in 2013 (and my 1st race in 30 years lol ). This happened on the first time I really gave it WOT down the home straight at Snetterton, when I opened it up again after going around the corner, absolutely nothing! I thought the ignition had failed but examination in the pits revealed a similar neat hole in the top of the right piston. What puzzled me is that I should have had at least a 250cc single engine firing but nothing at all. When we thought about it we determined that the breather hole in the fuel cap was not up to the job of twin 38mm Mikunis drinking fuel at the maximum rate. This caused fuel starvation and it holed the piston (that pot also had a slightly tighter squish which probably did not help). After replacing the pistons and opening up the cap breather we had no further issues, at least from that problem .

Cheers Geoff

[ChrisK]

Thanks Geoff, I do remember you mentioning the breather problem some time ago and so I took note and made a separate 1/4" breather outlet in the tank. The overheating was on one side only so I think it was a single side air leak issue, plus it had been running strongly all weekend (apart from all the other issues!) so I think if it was a breather it would have manifested itself earlier. I'm only on the 34's at this stage too.

[ChrisK]

With the front end chatter, if it's a frame resonance issue it might be a pain to fix. Tow suggestions: Try more weight (yours) over the front end to change the ratio of sprung to unsprung weight and throw both disks away and fit one from Manta. It's the only semi floating disk that's approved as a replica of an RG500.

If that doesn't work try different forks that resonate at a different frequency and see if that odes the trick.

Thinking about what you say with the forks, I might try a decent fork brace to see if that does anything. These forks are 35mm, up from the standard 34, and have full Maxton GP20 internals. I have played with comp/rebound settings but nothing seems to change. At the moment I can't get my weight any further forward with that tank/seat combination but it it weird that the chatter seems worse when the front end is loaded (going in to the corner), as soon as I get on the gas (weight off the front) it reduces. Going to try a shorter swing arm which will effectively move the weight bias more towards the rear. I might try seeing if I can work out the F/R bias as it is, I assume you just put each end of the bike on a scale and see what it reads? I know the John Player Norton from '73 had a similar wheelbase and had a 48/52 bias.

[link]

Hi Chris I was hoping to get to the island classic to see the bike in action. Its a real shame about the piston. Earlier you spoke of radical porting etc on a new motor that will be cool and i would love to know more. I know of a few race ones but std heads seem to fail a lot maybe that coursed the lean out. would be great to chat some time Thanks Link

[Zunspec4]

Hi Chris,

We were also getting bad chatter with the Seeley at Pembrey. I fitted a wider front (110 Avon AM22) which may be the cause, when the 90/90 AM26 was fitted we had no chatter. I have gone back to the 90/90 but have not yet had it back on the track, I'll let you know if the narrower front returns the bike to good manners.

Cheers Geoff

[ChrisK]

It's interesting you have found that to be a problem, Geoff, at the Island someone diagnosed that as a potential cure for my chatter so I bought a new 90 there and had it fitted - no difference! Another rider did tell me that when they went from Avon to Dunlop the problem went away for them (350 Yam), so who knows. I'm somewhat heartened that a Seeley can have the same issue as my backyard job though

By the way, I think we may have found the issue causing the lean running on one side. It was always the left, so I swapped the carby and carby mounting to the right and the problem transferred to that side. All the standard leakdown tests had showed no problem in the motor itself but when I sprayed some carb cleaner around the carb intake mounting it suddenly stalled. So we are pretty sure it is the Cruizin Image carby boots that are leaking somehow. I have some genuine Mikuni manifolds and boots on order so hopefully that will cure the lean running problem and I can actually get some track time. This thing has been doing my head in! As it happens I've been on the sidelines injured anyway after a crash on the Supersport bike in qualifying a month or so ago so I couldn't have ridden anyway.

Kev Fawsitt kindly gave me some 750 rods so the next stage of the motor development will be to build a new crank and decked cases with those at some stage.

Cheers
Chris

[ChrisK]

Hi Chris I was hoping to get to the island classic to see the bike in action. Its a real shame about the piston. Earlier you spoke of radical porting etc on a new motor that will be cool and i would love to know more. I know of a few race ones but std heads seem to fail a lot maybe that coursed the lean out. would be great to chat some time Thanks Link

Thanks Link, I'll give you a call and have a chat.
Chris

[Zunspec4]

Hi Chris,

My bike will be out at Cadwell Park in a weeks time so I will report on any chatter issues with the 90/90 front.

Regarding carb manifolds - I am using those sold by Motocarb, they directly bolt onto the barrels. They also do replicas of the Suzuki items which fit the std. alloy stubs.

http://www.motocarb.com/adapters--connectors.html

Cheers Geoff

[tz375]

Chris,

I have been digging through my files and I can't find the Manta web site anywhere either. I know I have checked them out because they are or used to be the only people in OZ that made/sold replica XR floating disks. They were used extensively by guys running P5/6/earlystocks GSX1100s etc, where they can only use period parts and the only legal floating disks were from the square four race bikes.

I wonder if they advertise in AMCN. If not, sniff around the pits at some of the 4 bangers and see what rotors they are using.

Some (many) years ago I tested a Kawasaki A7R replica at a Broadford practice day. It had a GT750 front brake and that thing chattered something terrible around turn one-two at my moderate speed. That front wheel assembly was just out of synch with the springs and damping in the RD forks it was running. The faster I went the worse it got and it wasn't a balance issue - just round that long sweeper at speed.

Hope a 90 section tyre fixes it for you.

[ChrisK]

Thanks, do you reckon this might be the same mob? http://au.ypgo.net/Manta+Enteprises+Hei ... 4518100445" onclick="window.open(this.href);return false;

When I get this thing running properly I'm going to pull one of the discs off and just see what that does. That front wheel is like a ton of lead!

[tz375]

Could well be the place. Worth a quick call I reckon.

[Zunspec4]

Hi Chris,

For reference, I am using a single disc (GT 750/500 EBC but thickness of 5mm vice 6.9mm std) with the AP Lockheed twin piston calliper with EBC "green" organic pads. Gary reports that the front brake is very good although the disc does show the affects of getting pretty hot. We still had chatter though despite the Maxton bling forks , we suspect the wide 110 section tyre.

Cheers Geoff