A different oil cooler

I fear that an XZ with sidecar has even more problems with hot oil, resulting in burned stators. I studied Lucky’s beautiful oil cooler and I used this as an inspiration. Very clever oil cooler made with much knowledge on the internals of the oil system of the XZ.

BUT: is it possible to have an oil cooler that does not require cutting thread in the engine, or, is it possible to have an oil cooler that is interchangeable between XZ’s?? Other idea: use as much XZ parts as possible because I have a spare bike.

The only obvious place for fittings to and from an oil cooler is the oil filter housing. So seeing where the oil enters the oil filter housing and where it leaves the oil filter, I started to think of separating the IN and the OUT of the oil filter housing.

I thought of the following construction:

Ingredients: three XZ oil filter housings, an iron plate of 5 mm thickness and ca 100 x 100 mm length and width, an iron pipe between this plate and the crankcase, a rubber of an XZ air filter, and an oil cooler including pipes and fittings of an XJ-model: a 600, 650 or XJ900 of the 80’s.

Two oil filter housings were cut and made completely flat by a friend with a lathe.

I cut and filed the 5 mm iron plate, made holes in it, tapped three 6 mm threads in it and welded a short pipe on it on which a rubber oil seal of an XZ oil filter fits.

All parts were fitted with Yamabond or Locktite 510 oil/heat resistant sealer.

I cut part of the XJ oil cooler house (the round house between crankcase and oil cooler pipes, see photo above, left) and filed it half-round to fit the curve of the XZ oil filter housing. I bored holes and bolted this fitting to the XZ filter housing using Locktite 510 or Yamabond. On this fitting you can screw the O-ring fitted line that brings the oil to the cooler itself. I needed an extra spacer in between (right photo above, right forefront) because the oil pipe just touched the bottom of the XZ crankcase without this extra spacer. It is made of aluminum, and, therefore, easy to cut and file and bore. You see all mounted in the photo left below: three parts: screwed on the filter housing is the piece made of the XJ-part of the photo left above, on that comes the spacer of 6 mm aluminum and on that comes the O-ring using end of the oil pipe. Two screws and nuts fit the part directly to the filter housing. Both other parts are screwed to this using the internal thread in the XJ piece; all connections are leak-free probably thanks to Yamabond that is used at the connections.

The return-pipe is fitted to the end of the filter housing (C) by thread (thick wall part and by thread + nut (thin wall part), see last photo right.

I prefer this place for the return-line because I fear that fitting it to the side-wall of the filter-house (such as I see in Lucky’s construction) may damage the oil filter. Lucky explained to me now that he fits the metal strengthened part at the location of the oil entrance. It depends on the strength and pressure of the oil, but with this end fitting the force of the oil comes at the metal part of the oil filter strengthened by a flat metal washer (see picture). The disadvantage of my construction may be that the oil pressure opens the relief valve at the end of the oil filter. I changed the construction now by putting a round metal plate (actually a 50 eurocents coin that fits exactly) at the end with a 5 mm and a 3 mm hole in it. In this way the full oil stream cannot open the relieve valve easily, but in the unlikely event of a filter blockade oil can still pass through the relieve valve.

The rubber seals between the filter housings and the iron 5 mm plate are XZ parts. They were cut from the rubbers between the air filter housing and the carburetors.

The oil cooler for the sidecar-XZ was the first I made. In the mean time I prepared a second metal plate + pipe, obtained extra filter houses and thought of a better, easier construction. I bought JBWeld and I think of gluing the housing A to the metal plate and gluing the oil lines to their filter housing, gluing filter house B and C together and only keep the rubber fitting between iron plate and filter house B to be able to change the oil filter. I would prefer an copper ring here but I cannot find one of the proper size up to now.

Disadvantages of this construction: many connections that should be oil tight, and a construction that protrudes wide to the right, in such a way that it may be easily damaged by dropping the bike. For a XZ with sidecar no problem, for a solo-XZ I have to think of some way to protect the construction.

The total construction should be precise and free from internal leaks. If not (part of) the oil bypasses the cooler and filter. There is no control on this, except a check that the cooler indeed becomes hot.

Advantage: it seems to work: the oil cooler becomes hot. This construction cools the oil and it makes the oil quantity ca 0,3 liter larger, which is 10% of the original. Not only the oil cooler capacity but also the capacity of the extra filter housings. Also the addition to the quantity adds to the cooling effect. I intend to paint the three filter housings black, perhaps still adding a bit to the cooling effect.

XZv2