TZ250G Restoration

OK Guys, show what you are building/restoring! You do know we love lots of pictures?
admitnothing
Posts: 28
Joined: Thu Jun 09, 2016 8:13 pm
Location: Lake Tahoe, NV area

TZ250G Restoration

Postby admitnothing » Thu Feb 08, 2018 9:49 pm

I have finally started tinkering with the restoration of my 1980 TZ250G. When I bought the bike back in the mid-90's, the chassis was in fairly stock condition with the exception of wider wheels and an oversize front rotor and an AP caliper. The engine has a 1H301 cylinder on a set of DS7 cases and some non-powerjet 34mm Mikunis. It came with a few spares including another set of DS7 cases, a couple of 4A1 cylinders in decent condition and some lightly used 4A1 pistons. I tried to start the engine several times after I got the bike, and got it to briefly fire on a couple of occasions, but I quickly lost interest with it and relegated it to the barn where I have occasionally lifted the cover and looked at it over the past dozen or so years. I have always wanted to restore the bike to its full 4A1 glory and to that end, I have been buying NOS or good used parts off e-Bay for the last 7 or 8 years, when I found items that I thought were not overpriced. I now have an NOS set of 4A1 pistons, rings, pins, rubber manifolds, etc. and recently acquired a set of used 4A1 cases from the UK for the princely sum of $175.00 including shipping. They look a little rough because they had obviously been outside in the weather at some point in their recent life, but I think they will still be quite serviceable. I am getting them ready right now to ship down to Tucson to be vapor-blasted at Restocycle.

So, I am looking for a little input. I will need new cylinder studs when I get the cases back and have read the thread on this website about stud lengths. The 94mm-long studs (90116-08213-00) are NLA but are occasionally available on e-Bay for ridiculous amounts of money. All of the bottom crankcase studs are still available from Yamaha, so I was wondering if I could use the 97mm-long stud (90116-08064-00) in their place? They look quite similar, but perhaps there is a difference in the material used, because the 3mm additional length shouldn't be an issue. When the time comes to install the new studs, do I just bottom them out in the case with a drop of green Loctite?

Also, these used cases came with 2 of the front rubber mounting dampers and the damper tube missing, but the remaining 2 are in rough shape and may be corroded in place. The remaining damper tube makes it impossible to push the dampers out from inside of the mounting bosses. Does anyone have a good suggestion for removing the dampers? I haven't put much effort into this yet other than to spray them with some penetrating fluid. The dampers are still available from Yamaha, and I will probably be contacting Gordon Jones for a new set of damper tubes in the near future.
To be perfectly honest, I still haven't decided what my final goal is with this project. I know that I would like to do an accurate restoration, but do I want to get it track ready for the occasional track day, or just settle for a static display that could be fired up occasionally and ridden in my neighbourhood? I have toyed with the idea of restoring the chassis and doing a proper 4A1 engine rebuild with the parts I have acquired, but then putting the RD400 engine and expansion chambers I have on the bench into the chassis and adding some lights so I can ride it here in the mountain twisties for a year or two before putting it back to race trim.

I haven't opened the DS7-cased engine yet, so I don't know how much of the internals are actual TZ or RD, and in what condition they are in. I suspect that the acquisition of that knowledge may be the determining factor in which direction I go with this project.... I don't think I want to spend 8K to restore a bike that is ultimately worth 6K. Some items that I am still missing like the 4A1 carbs will be expensive and difficult to find, and I need to have the dents taken out of the fuel tank. The alternative, and it would really be tough to give up on my dream of a full restoration that can be ridden in anger, would be to part this bike out. It still has many of the hard-to-find stock parts on it, like the kill switch, choke lever, throttle housing, tach, water temp gauge, rear caliper, etc. All of which are in very good condition and would certainly help others to finish their own restoration projects if I made them available.

I know a couple of the posters on this board are interested in purchasing a project bike from this era, but until I decide what I want to do with this endeavour, please don't ask me to sell it to you because I have 5 other restoration projects going that need to be financed. The temptation to take the easy way out and give up on the TZ, may cloud my judgement. In the meantime, any and all suggestions or comments, particularly on the questions I asked above, are welcome.

170plus
Posts: 141
Joined: Mon Sep 14, 2015 3:05 am

Re: TZ250G Restoration

Postby 170plus » Fri Feb 09, 2018 2:49 am

Just a couple of quick thoughts...

The TZ exhaust will not fit directly on the RD400 cylinders - different attachment.

The 250G carbs are PJ 34mm Mikunis with 'long' inlets - they do pop-up from time to time on eBay.

The 250G was notorious for eating pistons - 80 miles and they are done. This is probably the reason it has a 250 E/F (i think) cylinder on it.

The 3mm extra stud length should not be a problem - the nuts should cope with the extra length -it's amore of a problem if using the 350 cylinders with them. As for different material - you give Yamaha too much credit! 100% sure it's the same..

Kerry

Northracing
Posts: 176
Joined: Thu Sep 10, 2015 1:41 am
Location: Northwestern Canada

Re: TZ250G Restoration

Postby Northracing » Fri Feb 09, 2018 3:57 am

Nice go see another 250G project out there. I have a 250G as well, bought in late 90s. I ran it as a 250G for a couple of years and then converted it to a 350G and raced it for several years until the frame cracked and I decided to retire it. I will be restoring it as an original 250G and hope to start the work in a few months.

A couple of things, they were piston eaters but at the same time, a quick bike, as quick as a stock H-J TZ. Also, no choke lever was fitted to the G bikes, the enrichening circuit is a pull-up knurled brass knob on the 34mm PJ carbs. As Kerry noted, carbs come up, my bike had Lectrons and I found an original pair of 4A1 carbs on ebay a couple of years ago for a decent price.

If your DS7 engine has a wet clutch, it likely has a street gearbox, the input shaft is longer with the dry clutch and the wet clutch primary cover won't fit. Stock primary cover on the G was magnesium and notorious for being porous or cracking so oil seeps were/are common. TZ gearbox parts are being made again but pricey.

Most parts are out there if you're patient.

Derek
:shock:

admitnothing
Posts: 28
Joined: Thu Jun 09, 2016 8:13 pm
Location: Lake Tahoe, NV area

Re: TZ250G Restoration

Postby admitnothing » Fri Feb 09, 2018 5:20 pm

170plus wrote:Just a couple of quick thoughts...

The TZ exhaust will not fit directly on the RD400 cylinders - different attachment.

The 250G carbs are PJ 34mm Mikunis with 'long' inlets - they do pop-up from time to time on eBay.

The 250G was notorious for eating pistons - 80 miles and they are done. This is probably the reason it has a 250 E/F (i think) cylinder on it.

The 3mm extra stud length should not be a problem - the nuts should cope with the extra length -it's amore of a problem if using the 350 cylinders with them. As for different material - you give Yamaha too much credit! 100% sure it's the same..

Kerry


Thanks Kerry,

I have a set of RD400 expansion chambers as well, just have to make some mounting plates if I go that route. Thanks for the insight on the studs.

Steve

admitnothing
Posts: 28
Joined: Thu Jun 09, 2016 8:13 pm
Location: Lake Tahoe, NV area

Re: TZ250G Restoration

Postby admitnothing » Fri Feb 09, 2018 5:30 pm

Northracing wrote:Nice go see another 250G project out there. I have a 250G as well, bought in late 90s. I ran it as a 250G for a couple of years and then converted it to a 350G and raced it for several years until the frame cracked and I decided to retire it. I will be restoring it as an original 250G and hope to start the work in a few months.

A couple of things, they were piston eaters but at the same time, a quick bike, as quick as a stock H-J TZ. Also, no choke lever was fitted to the G bikes, the enrichening circuit is a pull-up knurled brass knob on the 34mm PJ carbs. As Kerry noted, carbs come up, my bike had Lectrons and I found an original pair of 4A1 carbs on ebay a couple of years ago for a decent price.

If your DS7 engine has a wet clutch, it likely has a street gearbox, the input shaft is longer with the dry clutch and the wet clutch primary cover won't fit. Stock primary cover on the G was magnesium and notorious for being porous or cracking so oil seeps were/are common. TZ gearbox parts are being made again but pricey.

Most parts are out there if you're patient.

Derek
:shock:


Thanks Derek,

I have the magnesium cover and a dry clutch on that engine, so at least some of the internals are TZ. I am always on the lookout for the carbs, but the other parts I'm looking for are the ignition cover, and the sprocket cover. I have seen the FRP reproductions available in the UK but will keep looking for originals.... don't need them til the very end of the project, so may resort to the repops to get it finished and keep looking afterwards.

Steve

M.duMaine
Posts: 374
Joined: Thu Sep 10, 2015 6:26 pm
Location: Curacau - Dutch antilles

Re: TZ250G Restoration

Postby M.duMaine » Sat Feb 10, 2018 12:11 am

Also a good Idea when using TZ 250 G cylinders is to bore them out to 56 mm and use 26J pistons.
Carbs you can use Lectron 36 mm...works very fine and is periodic..!

Michel

Ronan
Posts: 89
Joined: Fri Oct 30, 2015 10:10 am

Re: TZ250G Restoration

Postby Ronan » Wed Feb 21, 2018 2:59 pm

If I recall correctly someone did a mod whereby they welded and machined the cases on the G and reversed the cylinder and pistons, to save the inlet skirts of the pistons...

admitnothing
Posts: 28
Joined: Thu Jun 09, 2016 8:13 pm
Location: Lake Tahoe, NV area

Re: TZ250G Restoration

Postby admitnothing » Wed Feb 21, 2018 11:35 pm

I was looking at some of the spares I got with my 1980 G project, and found a second set of DS7 cases. These ones have the front rubber mounts, and the serial number indicates that they are from a 1979 F model. The online parts lists (Yamaha USA, boats.net, etc.) show the part number (1H3-15100-00-00) as being the same for all years of TZ250 from 1976 thru 1980. Yet there is a significant difference in the area in front of the shifter shaft boss on the two sets of cases. My question is: Does one of these sets of cases have the wrong bottom half on it? Or has the 1H3 part number just become a default number in the online parts lists because all of these cases are NLA. I have a printed (PDF) parts book for the F model, but not the G. In the F book, 1H3 is the number listed. Is the bottom case on the G model unique to that year?
Attachments
DS7 case.jpg
DS7 case.jpg (172.47 KiB) Viewed 67 times
4A1 case.jpg
4A1 case.jpg (165.94 KiB) Viewed 67 times

admitnothing
Posts: 28
Joined: Thu Jun 09, 2016 8:13 pm
Location: Lake Tahoe, NV area

Re: TZ250G Restoration

Postby admitnothing » Thu Feb 22, 2018 12:19 am

Similar question on 250 heads: When did they change from the concentric combustion chamber to the non-concentric? I have not pulled the head from my engine yet..... is there an easy way to tell from the exterior? Are the spark plugs canted forward?
Attachments
1980 250.jpg
1980 250.jpg (162.15 KiB) Viewed 66 times
1976 250.jpg
1976 250.jpg (169.62 KiB) Viewed 66 times

M.duMaine
Posts: 374
Joined: Thu Sep 10, 2015 6:26 pm
Location: Curacau - Dutch antilles

Re: TZ250G Restoration

Postby M.duMaine » Thu Feb 22, 2018 12:41 am

Actualy it's anyway better to use heads with inserts and center plug.
They can be easily machined in a CNC lathe from high grade alloy. :D

All the non concentric heads have spark plugs at an angle, easy to see.
I never was a fan of them, also when set up with a good squish they needed very high octane fuel and with that it's difficult to set up.
Also the metal quality from the OEM heads was often suspicious. :oops:

Michel


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