GT750 Milky trans oil

[motokeb]

I'm a newbie (to 2-strokes anyway) and just resurrected a 1972 Buffalo. The poor thing had apparently been sitting for years, and the crankcase mostly just contained white sludge. I drained it and refilled with motor oil before my first startup, and warmed it up about 4 times on the center stand to work out the bugs. Today I drained the motor oil (which was now white like the old batch), gave it fresh 15W-40 and took it for a 10 mile test ride. The bike performed beautifully at first, then began to run rough at idle and throttle response became sluggish (from idle) but still blipped nicely at higher RPM. When I got back I noticed foamy oil oozing onto the ground from somewhere (couldn't tell where). I unscrewed the seep-hole to check and probably close to a quart of milky oil came gushing out.

I may be dealing with separate issues here, so here are a few more details:
First, when the bike started running rough at idle I switched off the headlight and *thought* it improved. The neutral light was barely visible by the time I got back, so unless my eyes were playing tricks on me I'm thinking it's a problem with the charging system. It still accelerated well with moderate to heavy throttle. I'll have to get my volt meter out tomorrow to see.
Second, and what really concerns me, is why the oil level ROSE and TURNED WHITE AGAIN. I filled the crankcase by measuring out 2200 cc, but when I got back it was clearly over-filled. I'm praying it's not asking for a major overhaul! So I have two questions: first, is it possible it's the o-rings in the waterpump assembly? I didn't have a tach cable when I started this project, so I didn't realize the nylon water pump gear was toothless for the first few times I ran it. I don't think I would have overheated it just running it on the center-stand but have no way to say for sure. There are no leaks visible around the water pump cover. My second question is whether a cylinder leak down test would be a good way to find out where the problem is? Thanks for the help!

[two-stroke-brit]

hi there motokeb welcome to the board lots of helpful peps on here.
sounds to me that you have water contaminating the engine oil.
how is the water level?.
on a selfish note i would love to see some pics .
cheers mark

[Barry S.]

Foamy transmission oil can be from bad crank seals as these old bikes are notorious for the seals going bad after sitting for many years. There is a crank seal between the right and center cylinder that is exposed to the trans oil, if it leaks it pressurizes the transmission and causes it to blow out oil from the breather near the oil pump on top of the cases. Mine did this and it fouled plugs and required a tear down with new crank seals. They don't make these old bikes anymore so it's probably worth the effort to rebuild it, just up to you and your wallet.

[Cliff]

Check the coolant level in the rad. Was it full before?? Is it low now??
Oil mixed with coolant will turn milky. My guess would be a faulty water pump.
A quart over filled? Where did that extra quart come from? At today's oil prices, if you're making oil you're going to be a rich man!!

[motokeb]

Thanks all for the replies. Barry S. You probably nailed it with the crank seals--in just 10 miles I went from clean properly filled oil to the crankcase oozing out anywhere it could. I won't have time to begin working on the re-build for at least a couple months. When I do that I'm going to take my time and clean/paint/polish everything as I go.

Here are some pictures of what she looks like now. I patched up the abused old tank and painted it in my basement last winter.

[tz375]

Could be seals but milky is usually a sign of water. Dead crank seal will push clean oil out of the bottom end.

Most likely is the water pump. Remove the tank(s) and center pipe and throw it on its side. Then pull the pump cover and impeller and remove the pump and repair/replace it. If that doesn't fix it, the motor has to come out.

[Coyote]

I had the same issue with my 77 750. Put some extra stop leak in the coolant. Get the liquid stuff suitable for aluminum. The o-ring that seals the tranny from the water punp eventually swelled up and quit mixing the two. As in your case, mine had sat for 25 yrs.
Sadly, that seal replacement requires splitting the cases. I guess I just got lucky for once.

[Suzsmokeyallan]

This is coolant in the oil and that can only come from a few sources. Since its a 72 model theres a chance the sealant joint at the bypass has failed between the case halves. The 72s do not carry an o-ring at the case halves which means they do leak from age.
Its also possible the water pump oil seal has failed too but then the weep hole at the impeller cover should be spewing out some residue unless its blocked by dirt.

I'd follow Richards first plan of attack and go for the water pump cartridge first, BUT before you do and get annoyed and frustrated, you need to follow this thread to make removing the cartridge EASY. viewtopic.php?f=9&t=1956" onclick="window.open(this.href);return false;
Once you have it out, you will know if it was in fact the culprit by seeing the milky residue around the upper part, if not at least you can refurbish it now its out.

[motokeb]

Good info. I pulled the water pump (drilled a hole to tap it out -template measurements were perfect) and it did not appear to have oil/milky oil anywhere but the top, but then again it was hard to tell after the lube sprays and prying. The o rings look nice and the impeller was perfectly clean.

I think I bent the impeller trying to pry it off, though, so I removed the water pump from my '74 parts engine. While my '72 pump shaft turns freely in my hand without any resistance, the '74 pump is very stiff: looks like the oil seal under the bearing is clinging pretty hard to the shaft.

So, for the rebuild it looks like the o-rings and the bearing are available for cheap, but where do you get a new oil seal? How do you get the bearing and seal off? Do you think I should just buy a water pump rebuild kit from Crooks? I'll have to refurbish the '74 pump because that one has the impeller intact and it doesn't look like you can swap impellers.

Also, Allan, I hadn't heard of the "sealant joint at the bypass" yet. Where exactly is this? I suppose there's nothing I can do about it anyway, so after I put the refurbished water pump back it will either be fixed or need a total engine re-build.

Thanks again for the help.

[oldjapanesebikes]

Crooks does sell a full water pump rebuild kit - fairly reasonable as I recall. Just give them a call if you are in the UK as I'm not sure how its listed on their site.