GT750 Drag Bike

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ja-moo
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Re: Progress for 2009

Post by ja-moo »

water cooled wrote:Among other things, I thought I would try my hand a learning to fill tank dents...chemically stripped original paint then applied two coats of light filler. Still needs another pass to completely fill the bigger dents on the right side.
You will drive yourself crazy trying to get the bondo to "match" the tank if you are trying to finish sand it like it looks in the pictures. It will always show. Sand till the bondo is still "high", and then throw on a few heavy coats of primer. Then finish sand from there. It will take a few sets of coats, but if done this way, no one will ever know there is filler.
Visiting from the "K" camp...........
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water cooled
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Post by water cooled »

I was looking for some 100 grit paper but only had the 220...but are you saying that I shouldnt sand it down that close to the bare metal or feather the edges before priming?

I still have at least one more pass I need to make on the bondo to fill all the dents so I'll try a lower grit paper and post another pic before I prime it.

Thanks for the advise...its my first attempt at this
ja-moo
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Post by ja-moo »

water cooled wrote:I was looking for some 100 grit paper but only had the 220...but are you saying that I shouldnt sand it down that close to the bare metal or feather the edges before priming?

I still have at least one more pass I need to make on the bondo to fill all the dents so I'll try a lower grit paper and post another pic before I prime it.

Thanks for the advise...its my first attempt at this
You just need to leave it a bit higher than the metal surface. Use the primer to build up as you sand down.
Visiting from the "K" camp...........
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water cooled
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GT 750 Dragbike

Post by water cooled »

This weekend, I spent a little time getting the cylinder head gasket fitted. The most significant advantage of the copper gasket is that the bore fits more closely to the cylinder bore as compared to the stock head gasket. The gasket I am replacing was used in later model GT750's and is much thinner than a stock gasket for a 74 model, but very close to the same size as the copper material. However, a little trimming is needed on the copper to make sure everything fits properly.

The procedure I used was to place the copper gasket in the optimum position relative to all three cylinder bores and then secure it from moving by using some 8mm x 25mm bolts with fender washers.

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The 10mm bolt holes are trimmed up easily with a chainsaw file and then gone over with a finer file. Here, all the 10mm bolts are checked for clearance and the bores are fine finished to remove any flashing that hung out into the bore.

Only three of the 8mm bolts holes required additional work to open the hole up for proper clearance. Tomorrow, the barrel and head go out for milling and the copper will be annealed to soften it.

Image
Last edited by water cooled on Sun Apr 19, 2009 6:50 pm, edited 1 time in total.
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water cooled
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Post by water cooled »

I put another skim coat on the tank to finish filling in a nasty dent that was on the right hand side. Tonight it will get a sanding with some 100 grit paper and ready for a few primer coats over the next few days.

Image

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Last edited by water cooled on Sun Apr 19, 2009 7:19 pm, edited 1 time in total.
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Suzukidave
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Post by Suzukidave »

Nice work Kevin , those bore's are lined up perfect :D
the older i get the faster i was
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water cooled
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Post by water cooled »

Here is a pic of the aluminum lift plate set in place to raise the barrel 1.07mm. The barrel will get that much removed from the deck and after some compression tests, as much as .5mm more off the head to raise the compression slightly.

Image
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water cooled
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Post by water cooled »

Dave, I couldnt have done it without you and a few others that offer their help and advise. Thanks for the gasket and install tips.
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water cooled
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Exhaust Gaskets and JEMCo

Post by water cooled »

I noticed recently that the stock exhaust gasket PN 14181-15010 has a smaller ID than that of the JEMCo pipe and a smaller OD than the exhaust exit on the cylinder block. When a JEMCo pipe is mounted to the cylinder block, the gasket could end up just about anywhere but likely, during installation, it drops to the bottom of the cylinder block exhaust exit as the JEMCo pipe is mounted and secured. It is easy enough to stick your finger in the stub and try to orient the gasket so it is concentric but, dimensionally, the gasket is still hanging out in the exhaust flow and probably robs a little power from the performance...maybe not much, but some.

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Here are the dimensions I measured on my engine:

Cylinder Block - Exhaust Bore Dia: 2.20” (55.95mm)

Jemco Exhaust Nipple OD 2.12” (53.83mm)
Jemco Exhaust Nipple ID 1.91” (48.57mm)

PN 14181-15010
Stock Exhaust Gasket OD 2.15” (54.65mm)
Stock Exhaust Gasket ID 1.83” (46.50mm)
Stock Exhaust Gasket Thk .18" (4.7mm)

You can see that the stock gasket ID is about 2mm smaller than the JEMCo stub. If the gasket slides down to the bottom of the cylinder exit, it can be worse blocking more of the exhaust flow from the top of the exit.

If I did the math right, the stock gasket reduces the exhaust area by about 8% assuming it is relatively concentric when installed.

Bill Baxter recommended I contact Cometics and they now have an improved exhaust gasket PN: EX964094C which has a slightly larger ID than the mating JEMCo stub. It has a thickness of .094" (2.38mm) and is made of soft copper. Although it is about half the thickness of the stock gasket, it should still do the job. I ordered a set and will test them out in June.

In the image below, your looking down through the JEMCo stub. The dark ring on the ID is the portion of the gasket that is choking exhaust flow.

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Image
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Suzukidave
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Post by Suzukidave »

Kevin , just a thought .. how well does the Jemco exhaust stub fit up to the block outlet without the stock ex gasket . do you think you could leave the gasket out and seal the outside of the stub with some high temp silicone ?
the older i get the faster i was
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water cooled
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Post by water cooled »

Dave, thats what the H2 racers suggested also...lose the gasket and use VHT silicone. I can do that but the stub still has a little play in it and I was concerned the silicone would come free as soon as the stub starts expanding thermally.

Is this what the TR racebikes have?
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tz375
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Post by tz375 »

Another possibility is Gibson/Allspeeds from the UK. I have no idea what the ID of the header flange is though.

if not, it's RTV for you. Fortunately a drag bike only has to last about 10 seconds a ta time. OK so maybe 11 at the start of teh season. :D
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water cooled
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Post by water cooled »

Here are a few pics of the tank repair work after a few coats of filler and primer. I can see some areas where I could have done a little better, but overall I think it will work out just fine. The battery box is gone and will have a new setup to house the much smaller 12v 3amp battery.


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The RH side started off worse that the left. I had removed the lower fork lugs that limit the travel of rotation. Last year, the bike fell off the stand and the handlebars (throttle and master cyl body) did a lot of damage to the front corner of the tank. The frame is going off to the welders this week to get a limit-lug add back on as well as a dozen component mounting brackets for the new setup.

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Several engine mods got implemented this time around and the carbs were rejetted a little closer to where they should be...I have some brake work and wiring still to do. Wheelie bars are being stripped and repainted. Only 5 weeks left until the first race and a lot of little stuff to take care of.

Image

I need to find a decent portable compressor that I can take to the track for the sole purpose of charging the MRE bottle up after each races. The system is limited to 120 psig.
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water cooled
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Post by water cooled »

Here is an old pic from last years race at Norwalk. ...almost all the 2-stroke Kawasakis (and one Polaris) were in the 9's last year with the top guys in the 8's. Maybe 3 or 4 bikes were in the 10's or above so I have a lot of catching up to do.

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jaybob
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Post by jaybob »

Nice work on the tank repair. You are going to look better and be faster. What more could you want??
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