Stumpy

So I have a few questions for people who have rebuilt there engines. First I will list what I hope to do and then you can tell me what I am doing wrong or should be doing. Then I have a few questions ok.


I have an engine that I got when someone crashed there hawk so I plan on doing a whole engine carbs and all and just switch them.

• New higher compression JE pistons “what size rings should I use”
• I will not mill the heads to increase compression
• Moriwaki Cams
• Will have a shop in the area do a valve job and clean up the ports & time the cams “they have a flow bench”
• Mechanical CCT
• Replace what ever bearings that is needed mains and rods for sure.
• HRC carb kit

Now for the questions

• With the higher compression pistons should I put my 4 deg ignition advance on?
• What is the life of the timing chain should this be a must do replacement or if it is in spec should I be ok with it and if I do replace it should I put the updated chain, gears and adjustment hardware on it.
• Should I replace the valve springs and retainers even if they are in spec
• Should I lighten the flywheel Pro’s and con’s

Now for the biggest question I have so far has anyone ever cut the gears for better shifting I have the factory pro shift kit including the star wheel and it shifts good much better than before but can it ever be too good. I have access to machining tools and such as I work for the University of Wisconsin. If you have, do you have pictures of it or just what you did to them?

RCVTR

I'm sure you knew I would reply!

I was advised to mill .010" off the heads. When I slotted the ignition pickup to advance 4 degrees, I got detonation on pump gas at the track. The mixture will burn faster with higher compression. I don't think you'll want a 4 degree advance.

I later put an HRC ignition and full exhaust system on. I noticed some black soot on the muffler outlets at my home elevation a bit of hesitation at 7000 ft. so I went down a size on the main jets. I had mild detonation when I want to sea level. Jamie Daugherty suggested that it was from running lean. I think he was right. But I also think that high compression makes the engine more sensitive to those kinds of tuning issues. A richer mixture gives more evaporative cooling to the intake charge and keeps the pistons cooler.

I would say in hindsight that the benefits of higher compression are worth it for a track day bike, but don't shortcut the tuning process. I wish I had done some testing on the dyno. I will for my next one.

I have never heard of cam chains breaking. If you do replace them, replace the sprockets too. The valve springs should be fine. I just measured the free length. A spring rate check would be a good idea. But you are running stock rediline and should be fine IMO.

Got with stock Honda rings. JE Pistons are built for them. Replace the main and rod bearings-might as well while you have it apart.

I would recommend measuring the piston bores. Mine were out of round at the top. The RC51 I did had perfectly round bores. My VTR engine ran well, but burned some oil. Compression was very good. I think it was 145 psi in both at 6300 ft elevation. The stock bores tend to run on the high end of the range from the factory. JE pistons are built to the low end of the range. You end up with a lot of skirt clearance. I'm going to order custom pistons for mine, to specify a tighter fit, unless I decide to cut my budget. It will run fine with std JE pistons.

Take 1/2 inch off the flywheel diameter. You won't be sorry. It still runs great around town. That's a lot of rotating inertia with a wide RPM range.

I made no transmission mods.

RCVTR

that's just what I've learned from my experience.

Surely somebody else has something to add.

Hey Stumpy. I have an engine blueprinting spreadsheet. Do you want a copy?

8541Hawk

If you end up with the HRC jet kit, you are only going to want to use the replacement front slide and the needles. Don't plug the air bleeds and run the small jets unless you plan on running no air filter or no air box.

cliby

I'll second from all that and benefited from advice from both RCVTR when I planned my build and 8541 connected me with some HRC carb parts after the build. I tried all kinds of dynojet antics and dyno work and was unable to really get things perfect, until I went that route. I also got my engine from elsewhere, built over the winter and then swapped come springtime. Gave me lots of time and options. Since I didn't know the engine well, I replaced all the bearings when I did the work, though most measured within tolerance - it is so much of your labor that those parts become relatively cheap and not worth skimping on and you'll have an essentially new engine when done.

I reused the cam chains, but when checking the cam timing was off by 3 degrees - was that just tolerance or chain stretch? no way to know, honda doesn't give a spec for chain length anywhere, but all the advice I received indicated it was no problem to reuse them.

when you get to the engine swap, your not that far away from where I live and if you want to borrow the honda tools for the frame mounting bolts let me know.

bill

RCVTR

Bill, did you deck the heads? That would explain the timing error.

Another thing that people seem to ignore is the pitting of the valve faces. The exhaust valve faces will be pitted. It's just part of having a high RPM engine. The valve springs have to be stiff to keep the valves from floating off the cam lobes. You will probably want to replace the exhaust valves.

I had a couple of drinks with my frine Bob last night. We tried to keep from talking about motorcycles for a while, and caught up with family and work stories. But eventually I had to ask him a few questions about bikes. He still loves RC51s and wishes he never sold his VTR (it still makes him sick every time he thinks about it). Says he'll never sell another one of his projects. Anyway, he's really excited about my RC51 project. He told me some stories about the engine development work he did with piston designs, dyno testng with accleerometers on the heads to try and optimize combustion, VTR chassis mods. He carried a lot of the development work he did with the VTR over to the RC51 race engines. Man it was cool. In another life, maybe. I learned a lot. He also told me he has a stockpile of race parts I can pick through.

RCVTR

Also, since you are staying with the stock bores and stock piston size, you don't want to go crazy with the hone. You don't want to increase the skirt clearance on the pistons. If you are buying custom pistons, hone away.

I am a big fan of the 800 grit deglazing method I mentioned in another thread. It removes a negligible amount of material from the bore, but give enough crosshatch to seat the rings and let the bores hold lubrication.

RCVTR

Another thing Bob talked about was what it was like to ride a VTR with a heavily braced chassis and swingarm, 140 HP and racing slicks.

He said the *** end would just shake like crazy when he was hard on the gas. If he just stayed on it, the thing would settle down. People behind him wondered how he held on to the thing. I think it's similar to what the Ducati superbike chassis' sometimes do. He said if he raised up off the seat and leaned way up over the tank it got better.

The VTR was built to be a testbed for engine development for Superbike. Ducati had a displacement advantage. HRC took what was learned from racing VTRs and applied it to the RC51. All of the things that are different on the RC51 engine are from things that either broke or limited further HP. HRC had a rule of thumb that every 500 RPM in redline increase on the RC51 resulted in a 30 percent reduction in engine life. 11,500 RPM was reliable for a season. 12,500 RPM lasted one race.

RCVTR

I was just looking back at some old email correspondence. I found my old compression readings.

I had 156 psi front and 160 psi rear after a few break-in miles.

8541Hawk

he other thing that happens is that the cases end up getting destroyed at the swingarm mount, just like the Ducs.

JamieDaugherty

Maybe I missed a response to this, but I'll chime in anyway.

You should not mill the heads AND install JE pistons. That would cause valve to piston interference and also might bump the compression up too high. JE's compression is a little conservative, but even so you can go overboard quickly if you don't watch how much you remove from the heads.

RCVTR

I took .010" off.
I then reassembled the top end using the old head gaskets and put modelling clay on the piston domes around the valve pocket area. I installed and timed the cams, then rotated the engine through an entire cycle (two revolutions). Then I disassembled and sectioned the clay with a razorblade and measured the thickness. This gave me the valve-to-piston and squish clearances. There was plenty of clearance. I would recommend doing this, since you are changing cams and pistons.
Jamie, you are right to raise the issue.

I didn't CC the chambers and domes, but was told to expect ~11.5:1.

Also, Bill I think we had the same discussion about timing a couple years ago. Sorry to beat a dead horse and raise the obvious question again. Sounds like a lot of chain stretch, but it is a pretty long section of chain. I'm sure manufacturing tolerances in the engine stack up and account for some of the timing error.

RCVTR

I thought I had a picture of the clay with the valve imprint when I did the RC51 engine, but I can't find it. I didn't have a digital camera when I was doing the VTR.

The stage 1 cams are pretty mild, so there was something like .100-.150" clearance between the valve and the piston. It is a good exercise and gives a good picture of the engine in operation. Milling the head doesn't change the squish clearance. It was something like .060". .040" would be getting tight, due to rod stretch at high RPM.

This stuff is all basic VTR race engine recipe. It was all tested long before I did it.

Good luck with your build.

RCVTR

One more thing...

the engine is awkward to move around fully assembled. For the VTR I had a custom engine stand bracket that I borrowed. On the RC51 I assembled the bottom end, then mounted it in the nice, clean chassis. That makes a really nice assembly fixture. I didn't build a table, but next time I will have a 2 foot tall platform to park the bike on. It makes it much easier to work on.

JamieDaugherty

Are you sure about this? I've never seen an engine with over .100" of piston to valve clearance. Was this with stock or JE pistons?

RCVTR

JE pistons. Maybe it was .080 - .100". I don't have the measurement any more. I wish I had saved it. I know there was plenty of clearance, even with oversize valves.

RCVTR

Stumpy, I hope you find this info useful.

I know it's a lot more than I knew, when I started mine. And I haven't seen this kind of information made available anywhere else.

I like to write about it because it helps me to recall what I've learned and recognize what I want to learn and what i can do better the next time around.

Stumpy

Well been away for awhile and had to do some work on the computer. So I would like to thank all the response to this post.

First yes I would like a copy of engine blueprinting spreadsheet. Thank you very much rcvtr and do you have a photo of the engine stand I was going to try to make something temp maybe out of wood not the best choice but with out pic of one don’t want to take a lot of time making that and not my engine. Have been cleaning up my garage and got a heater will be doing more work on that tomorrow. In about 2 weeks I will start the engine teardown and see what I got at that point I am sure that I will have more questions for you all again thanks a lot will save me cash not going down the wrong road and having to do it over again.

Thanks

Stumpy

divingindaytona

I know I would love to take a look at the spreadsheet. I would bet others would interested in it too!

Would you consider posting it on the forum so all can enjoy?

RCVTR

Here's a couple bad photos that give the basic idea of the engine stand bracket. I snapped a few with a borrowed camera.

RCVTR

I have decided not to post the engine spreadsheet, because it's not really my work.

Basically it has all of the key dimensions and tolerance and an as-built measurement.

Cylinders are measured fore-aft and side-side at 3 heights. Roundness and taper are then determined.

I have measurements from my engine and the RC51 I did and one of Bob's engines for a customer.

My Superhawk was out of round by .004"
The RC51 was out by .003"
Dean's RC51 was out by .001"

I've been told they are typically out of round because the top of the cylinder is unsupported. They run fine, but it is a common cause of oil consumption.


Also - don't forget to cut a film canister and slide it into the lifter bores before removing the valves.

Stumpy

So I just picked up the pistons $220 for the hawk & will be taking the heads in to have the valves done along with cleaning up the ports $500 to $1000. Man this stuff costs not sure if it is worth it but doing it anyway can get some cash back by selling the motor that is in the bike if I have to. I am just about done with the garage has taken a lot longer than I thought lots of snow in Wisconsin. I am ordering a car engine stand and will make a modified holder so it will work with the hawk engine.

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=47304

Now a question about the HRC jet kit. I think I can still get a kit about $200. Is it worth it and do you know what all comes in the kit. I will have it dialed in on a dyno at Motorcycle performance in Madison Wisconsin.

http://www.Motorcycleperf.com

Would a factory jet kit work? Or should I get the HRC kit. Does it make that much difference? They made their first attempt at a world land speed record with a turbo ducatimotor in a frame they made. It made Motorcyclist Magazine last month. So anyway I will be starting the motor teardown in 2 or 3 weeks and I am sure to have more questions.

cliby

Stumpy, my experience was that jetting with the HRC needles and front slide was MUCH easier. I had reached a point of giving up using the dynojet with a compromise that left it either rich or surging. This was particularly worse after the porting and full exhaust and I think made worse by the dynojet drilling and lighter springs mods, but the needle taper was also wrong for it. Using DJ stuff it was impossible to get it right, and this includes dyno-work by one of the nationally recognized Vtwin tuners that happens to be in Minneapolis. The HRC stuff was much easier to get right using baseline recommendations and then some fine tuning. Again the needles and the front slide are the things that made the big difference. Mike from this site helped put me in touch with a guy who still had these parts.
would say 200 is cheap vs. frustration saved

bill

JamieDaugherty

A quick tip: The automotive engine stand won't do you any good. You'll want a decent sized metal top workbench.

RCVTR

???

If you want to take the time to fabricate a bracket, and engine stand makes it convenient. It will hold the engine at a good height and you can roll it over.

I have also done it on the workbench. Mine is masonite and works fine. Once I got the case buttoned up, I put the engine in the chassis and did the rest of the assembly there.

The engine stand is nice because of the work height. Once I was done, I lifted the engine with a comealong and lowered it to a crate, then set the frame over it. I ran straps through the top of the frame to keep from knocking the engine over. That way you can mount the chassis, then lift everything and mount the suspension with one rigging job.

For the RC51 engine, I carried the assembled bottom end to the crate, then lifted the entire rolling chassis over the top and lowered it in to place. The VTR is different because you don't have a rolling chassis with the engine out.

Would you believe I'm in Estonia right now? Looking out the window at Russian-built apartment buildings and across the river at Russia itself? Strange but true.

JamieDaugherty

Yes, but you only have to spin it around once! Everything gets bolted to the bottom end first, then you roll it over and do the top. Frankly, I think the engine stand would get in the way. Plus, how do attach the rotor/stator side parts? Again, a workbench is MUCH easier.

RCVTR

You haven't used one, but go ahead and argue anyway.

The engine is much easier to work on when it is rigidly fixtured. Ther is no comparison when you are torqueing the main and rod bolts.

It's just a question of whether you want to spend the time to make the fixture.

There is no interference on either side. It mounts to the engine mounting points.

out.