Some may remember I have had a few problems with my engine, after having a lower bearing fail on the rear cylinder con rod, I rebuilt the engine and everything was fine until the oil light started flashing on idle, so I fitted an oil pressure gauge and it showed the oil pressure rising and falling, on idle it fell to zero, after trying a few different oil viscosity's (I just didn't want to take the engine out again so soon) a thicker oil seemed to improve the oil pressure but the pressure was still rising and falling, so after many posts on here and much thinking I tried overfilling the engine with oil and adding an extra litre of oil the pressure stabilized so I had her tested for road use and began using her again, but over time I decided I need to sort this properly so out came the engine again. You may remember Cf Moto don't make oversize bearings for the crank but my local engineering shop found out that a certain model Toyota had the same size shell bearing so an over size set were ordered and the crank reground to fit, I had been convinced there was a part missing from the oil pick up on mine and had settled on finding this part missing, I thought I would buy the part and all would be fixed but when striping the engine I found nothing wrong, so looking at the crank the bearings seemed to loose I thought this is were I'm loosing some oil pressure, when I had another shop measure the crank they said it not the best regrind but it would not cause rising and falling oil pressure. so looking at all the parts for a few days and much head scratching I had a idea, when I removed the sump filter screen it had some build up of plastic in one corner which is directly under the passage to the oil pump, as the filter screen is flexible and the oil pick up is only about 5mm from the screen I think this is what's causing my oil to rise and fall, as the blocked part of the filter screen is drawn up by the flow of oil and sealing off the pick up port and as flow has stopped the screen springs back opening the port, I'm now fairly happy that's what's going on, the next question where did all the plastic bits come from and it turns out one of the original cam chain guides was wearing badly (the new ones I have are much thicker and seem to be made of different plastic)the plastic in the screen was from the chain guide, so that's the oil fluctuating sussed out, next was the low oil pressure. The bad crank grind was a factor in the low oil pressure but not the whole story, I have ordered a new crank and bit's from Mortch but they didn't sell all of the parts I needed so the other parts were ordered from a Uk dealer, back when I rebuilt the engine the first time I ordered crank shaft main bearings from Mortch who listed bearing with the red mark for crank shaft marked with a B, Mortch no longer sell these bearings so they were ordered form a Uk dealer for crank B and when they arrived they have a blue mark ?? I'm going to get the red and blue bearing measured but I wonder if the red bearings are too small and with the loose regrind on the crank lower end, I do wonder if this is were the oil pressure is being lost, hopefully the next few days will give me the answer, so it's seems bad luck may have had a part to play in my engine problems

[2015 Z Force 800 53/Trail EPS]

At least you have something "tangible" as to some of the causes. And hopefully the crank will get worked out....and I also hope the oil pump is still OK after all it went through.

One good thing is that the parts I've had problems with have been updated by CF moto, the oil pressure relief valve used to be a ball and spring (mine didn't seal properly) now they have a proper machined piston, the chain guide that had worn badly has now been beefed up with thicker part where the old ones wore out, the sump filter screen is now rigid so it wont flex like the old one does, the other upgrade is with the thermostat housings which are plastic, the new ones have metal inserts so they cant distort when tightening the bolts

ps, engine rebuild part 2 starts tonight

[2015 Z Force 800 53/Trail EPS]

ps, engine rebuild part 2 starts tonight

Good luck. Hope all goes very well for you.
I'm going to have to pull my rear gear case and find out what's going on very soon. I plan on having your old posts on yours help guide me.

It's not a bad job, if you want to check the gear mesh/backlash it can be a bit of a pain. I've just changed the oil in my diffs and it's completely clear

One thing I have learned on the 2-cyl CFM engines, is that engine case gasket sealing is very important. Use a new OEM case gasket to seal the case halves, and do not attempt to substitute with a liquid sealer or make-a-gasket, etc. There is a central cavity that requires case gasket to be completely intact in order to seal it for pressure and oil flow. If the gasket sealing was compromised on a rebuild, that may or may not have been the cause of your oil pressure issue. Also, replace your pressure relief valve as added insurance if you haven't already. Lastly, the CFM crankshaft plain bearing wear limit guidelines are pretty standard when compared to plain bearings in other motors, so if a reputable machinist decided the clearances were too big, it was probably time for a repair. Good luck on your next attempt.

I have to give praise to Cf Moto and say nearly all the parts that have given me problems have been modified/upgraded, one thing I had noticed on my last strip down was the piston skirt suffers from scoring and on the new pistons they have inserted a "Teflon" pad where the scoring occurs

Well the engine is back in and running, not without some disappointment though, when I started her first after a few seconds the oil pressure rose up on the gauge to 20 psi cold, I was hoping for more, anyway I gave her a blip on the gas and the oil pressure stayed at 20 psi, I'm now feeling a little disappointed after all that effort, then I thought about the oil cooler, in the past I have flushed the oil cooler lines with fresh oil just to clean the system, and noticed how much force it takes to push oil through the oil cooler, so I decided to by pass the cooler and what a difference the oil pressure cold jumped up to 40 psi and up to 60 psi with some extra rpm, so the engine is now fine, so I need to check the oil cooler hoses etc

Just as well I fitted an oil pressure gauge otherwise I would not have known, she had enough oil pressure to keep the oil light off but that was about it.

[2015 Z Force 800 53/Trail EPS]

Interesting...I knew the type they used wasn't near as efficient as the finned tube types but never heard anything about any restriction problems. Must be something in it or line...or a line problem somewhere. Well, there are lots better oil coolers out there.   

Hmm, that's good to know. A better cooler may not be a bad upgrade anyway.

Certainly a motivating factor for putting a gage to the engine out of an over-abundance of caution.

I wonder how difficult it would be to install a pressure sender/gage kit on one of these.

[2015 Z Force 800 53/Trail EPS]

Hmm, that's good to know. A better cooler may not be a bad upgrade anyway.

I use a 2-pass Perna-Cool unit on my Brute force. It took the sump oil temperature from 249F to 197F average and the hottest it ever got after the cooler install was 213F. The oil temp returning to the engine from the cooler was 172F average. And the first thing it hit was the crank, keeping it cool and not as expanded, which has to be great for the bearings. It did take a while longer to warm up though..but I was OK with that. The cam chains and tenioners nearly stopped stretching and wearing too. I'd like to see what these do. I think this summer I'll take a sump reading and see. If it gets above 220 I think mine is in for a new cooler.

[2015 Z Force 800 53/Trail EPS]

Certainly a motivating factor for putting a gage to the engine out of an over-abundance of caution.

I wonder how difficult it would be to install a pressure sender/gage kit on one of these.

Can't be too tough. Just pull the OE sending unit, install a "T" or "Y" fittings and screw the sensors back on. I would assume the threads are metric so that might be a challenge to get all the right stuff but...that's it. 

I have disconnected the cooler pipes at the front end and tried pushing oil back though both pipes and they are both very restricted, which if there was a blockage or similar I would have thought one would be restricted but both very unlikely, my thoughts have been for a while that the tube is too small for the distance they have to travel.
My test tonight seems to confirm this thought, the rubber hose is 10mm id the steel pipes are a bit smaller, i'll measure them later.

What are your thoughts please.

[2015 Z Force 800 53/Trail EPS]

I have disconnected the cooler pipes at the front end and tried pushing oil back though both pipes and they are both very restricted, which if there was a blockage or similar I would have thought one would be restricted but both very unlikely, my thoughts have been for a while that the tube is too small for the distance they have to travel.
My test tonight seems to confirm this thought, the rubber hose is 10mm id the steel pipes are a bit smaller, i'll measure them later.

What are your thoughts please.

Well, I know that most automotive oil coolers use a 3/8" ID line which had been fine for the volume needed for V-8s. I used it on my Kawasaki Brute Force which was overkill but obviously had no issues. It did have a 1/2" core tube but with 3/8" custom made steel armored high pressure line. More overkill but I never wanted any issues with line failure. I did blow through it before hooking it up and didn't sense any restriction. These are the lines I used on it: