ive just purchased a 1991 fj1200 that's been modified, the fairing has been cut above the inlet vents .ive looked at photo's online and it looks like those vents put
air to the back of the head, is it going to affect the cooling of the motor enough to cause problems ??
Welcome, do you have pictures to show what is cut and where?
this is how it is now
IDK. These things run pretty hot already. Then again, as long as it's moving, it my not matter.
The vents scoop air to the top center of the engine. The two cylinders on either end (#1 & #4) have the benefit of air passing along the side. So not having the scoops ducting the air will allow the engine to be a little hotter in the center. Since their is no place for the ducted air to pass through the center, between cylinders #2 & #3. I am not sure how much cooling takes place. But the air is hitting the top where it is the hottest so it is cooling more than without. Yamaha must have thought they were important. The scoop sizes got bigger from the first gen FJs scooping more cool air to the top. Randy at RPM has experience with cooling these air cooled beasts. The same engine is used in Legends racing where the engine is sideways in a small car. And the engines are run for 20 laps at redline so cooling is critical to keep things from melting and dribbling out the bottom during a race. For the casual rider it may not be that important. I am sure you are not the first with an FJ missing the side scoops.
thanks for the info as you can see from the photo Ive got a lot of work ahead of me and ive got a list of things that Im going too get from RPM
Quote from: FJmonkey on November 22, 2019, 09:50:00 PM
The vents scoop air to the top center of the engine. The two cylinders on either end (#1 & #4) have the benefit of air passing along the side. So not having the scoops ducting the air will allow the engine to be a little hotter in the center. Since their is no place for the ducted air to pass through the center, between cylinders #2 & #3. I am not sure how much cooling takes place. But the air is hitting the top where it is the hottest so it is cooling more than without. Yamaha must have thought they were important. The scoop sizes got bigger from the first gen FJs scooping more cool air to the top. For the casual rider it may not be that important. I am sure you are not the first with an FJ missing the side scoops.
I agree with all that Mark said and will add that I have it on good authority the inner cylinders are actually better cooled than the outside ones with the scoops in place. Also, the outer cylinders get some benefit from the ducts as well as the air being blown / sucked away from the inner ones flows over them.
The machine shop I use is motorcycle specific and has been in business since the early 60's and is 2nd gen, I doubt there is anyone in the country that has seen the inside of more bike engines than these blokes. The owner tells me FJ's show more signs of heat related wear on the outer cylinders than the inners, which suggests they are better cooled.
But in real terms this is only academic, just a bit of trivia, as Mark said, "...For the casual rider it may not be that important....)
I'd ride my bike without them (and have done) but I wouldn't
design my bike without them and air cooled lumps are much more forgiving than their liquid cooled counterparts anyway.
Noel
Oh boy, here we go again... :Facepalm:
Quote from: ribbert on November 23, 2019, 05:25:52 AM
...and will add that I have it on good authority...
Noel
FFS, you have got to be kidding me. :shok:
The cooling ducts are to properly cool the cylinder head and do not have any affect on the cylinder cooling.
Jono, yes the air scoops for the cooling of the cylinder head are very important to the proper cooling of the FJ engine. Without them there is not any direct fresh airflow to the cooling fins of the cylinder head and the head will overheat. This will cause the rubber valve stem seals to harden and leak, the valve springs become overheated and weaken and there is a possibility of so much heat generating pre-ignition can occur.
I would collect a set from Bob Weymouth (http://www.fjowners.com/index.php?action=profile;u=495 (http://www.fjowners.com/index.php?action=profile;u=495)) or ebay and get them installed to prevent over heating issues.
I do not recommend you operate that FJ without them in place and I would never do it. You are only going to create further issues down the road if you do.
Randy - RPM
thanks for that i will definitely fit some scoops the bikes been severely chopped but the motor is strong ill check the valves and seals first im going to get 1 of your solid cam chain tensioners and do the shims before i ride it
How do the Legends cars keep the motor from overheating?
I know they have a larger oil cooler but the engine is mounted sideways and gets no ducted air to it.
Quote from: FJ_Hooligan on November 24, 2019, 10:14:15 AM
How do the Legends cars keep the motor from overheating?
I know they have a larger oil cooler but the engine is mounted sideways and gets no ducted air to it.
Actually David, we duct more air directly to the engine than the motorcycle. Our heat issues come from running them at high RPM (WOT) all the time and running is a pack of cars without direct air flow.
The FJ has the front wheel & forks along with the header in the way of airflow to the cylinder cooling fins. I am very surprised Noel doesn't know this with his pedigree, vast personal knowledge and industry sources, but the two outer cylinders run the coolest on the FJ as the two inner cylinders are trapped behind the everything in front of the engine.
In the race cars we use a series of ducts, hoses & heat shields along with fans for air flow to the engine. That along with the larger oil cooling systems to keep the engines cool.
I have attached several photos of a four plenum ducting system from the front of a thunder roadster I maintain. I have built 15-20 of these systems in the cars raced in our region. It has the main larger plenum coupled with a duct under the header to supply the air to the cooling fins of the cylinders. The other three are for oil coolers.
Some people run a duct for cooling the head and others run fans. We run the duct as the ram air of the duct on my heads because in my experience and observations of the FJ engines cools better. It is grabbing outside air and ram feeding it to the head just like the side scoops of the FJ are designed to do.
The fans use a lot of under hood, heated air and just circulates it, but that is still air flow across the cooling fins and offering engine cooling.
I sell the two most popular fans for the cars as they are bolt on and no fabrication is required, so that makes them the most popular for the weekend racer.
RRC Top End Fan Kit (http://www.rpmracingca.com/proddetail.asp?prod=RRCFanKit)
Top End Cooling Fan Kit (http://www.rpmracingca.com/proddetail.asp?prod=TopEndCooler)
I have attached several photos of the cooling duct system.
Randy - RPM
Sorry for all the dust in the photos, the construction has really made a mess around the place, but they are paving tomorrow :good2:...
Quote from: jono on November 24, 2019, 02:16:38 AM
thanks for that i will definitely fit some scoops the bikes been severely chopped but the motor is strong ill check the valves and seals first im going to get 1 of your solid cam chain tensioners and do the shims before i ride it
Jono,
I would not recommend the manual timing chain adjuster. I do not use them and only have them for the guys that "Just have to have them".
I have seen much more damage with their use than from the stock tensioner.
Have a look at these photos from and engine with one...
The tensioner was over tightened. The chain wore through the rubber coating on the chain guide and you can see the wear that has flattened the top of the timing chain links. This engine once again is equipped with the stock
Yamaha Timing Chain Tensioner Assy (http://www.rpmracingca.com/proddetail.asp?prod=4KG-12210-00).
Randy - RPM
Thanks Randy.
The Legend Sedan I sometimes helped with didn't have anything like that ducting. I do recall a fan. But that's been over 20 years ago and I may not be remembering it correctly.
thanks for the info Randy i have just found 2 original air ducts for my bike i,m going to modify the fairing thats on the bike now which dosn't have scoops by adding after market ones ,its almost impossible to get fairing parts here but i want to keep it looking along the same lines as the original .at the moment its pretty much a rat bike but the previous owner looked after the motor and its pretty strong, ill go with a hydraulic tensioner like you suggest i cant see any way of checking the chain tension unless maybe from the top with the cam cover removed so setting the manual one would be pretty hard
here's a photo of what ive got to build from
What's going on with that muffler?
yes well mmmm the guy i bought it from chopped the whole bike the fairings the rear end and the mufflers it sounds pretty good actually but there being relaced as soon as i find a set of original mufflers ,i want to keep the motor pretty standard so i can tune it easily i havnt really ridden it yet and wont until ive done shims and cam chain tensioner
Was the previous owner going for the Mad Max look?
exactly its called street fighter style, unfortunately he didnt keep any of the cut off parts
Quote from: jono on November 26, 2019, 02:08:28 AM
yes well mmmm the guy i bought it from chopped the whole bike the fairings the rear end and the mufflers it sounds pretty good actually but there being relaced as soon as i find a set of original mufflers ,i want to keep the motor pretty standard so i can tune it easily i havnt really ridden it yet and wont until ive done shims and cam chain tensioner
Where about are you located I have a pair of stock mufflers... shipping is probably gonna be a bit pricey
I'm in New Zealand i would think postage would cost a lot due to the weight , i will find out how much though thank you ,are you in Maine?
Quote from: jono on November 26, 2019, 09:11:55 PM
I'm in New Zealand i would think postage would cost a lot due to the weight , i will find out how much though thank you ,are you in Maine?
Yea I'm guessing shipping would be there worth it