Wiseco Piston problem

[plasticadam]

I'm having to re-bore the FT and just want to retain standard compression on a single size overbore. Got a NOS Wiseco piston (correct part number) off Fleabay which I took to the engineer doing the machining and he said that it was hi comp and not worth using unless I wanted to stress the starter and do a load of other mods to make it run right. I didn't and returned it to the seller who has refunded (but not the $50 carriage or $30 import duty I had to pay in the UK).
Decided to cut my losses and pay for the full price piston from the UK importers. It was sent direct to the engineer to save time. I get a phone call from him to say its the same as the other one . I've looked at and its got a way higher crown with big valve cut outs compared to the flat topped Honda original. It is stamped with the correct part number as well. I am utterly confused. Still waiting after a week for some comment from the manufacturer (via the importer).
Question - this piston has been offered for years for FT/XL engines - has this question not been asked before? Has anyone got any experience of this and can you advise?
The only other piston I've seen available is manufactured by an Australian company called Forseti - does anyone know of them? They are loads cheaper than Wiseco and look much more like the standard piston, but I don't know what reputation they may have.

[J6G1Z]

I'm not familiar with the FT piston & the replacements available. Most folks want to raise the compression when they replace a piston. From what I hear, that is the main performance modification that FT's respond to the best, aside from a performance camshaft.

Do these replacement pistons have enough material in the top of the piston to machine the dome down or off completely?

As long as your starter has been maintaned regularly, you have a strong battery & you remember to prime the engine well prior to starting, you shouldn't experience much problem. I believe that the main trick to extending starter life on the FT, is having a good tune on the engine so it starts promptly. Prior to starting, I always rotate my throttle 4-5 times to operate the accelerator pump in the carb. This shoots a squirt of raw fuel into the intake tract with each twist of the throttle, providing a nice rich starting mixture & the bike fires right up without excessive cranking of the starter. Avoid the over cranking & your starter will last.

Good luck & please let us know what you find out.
J.

PS. You will gain some compression from the over bore even if you use a flat top piston. Embrace it, compression is not the enemy, poor fuel quality is.

[Slyphon]

Can you provide a link to the Wiseco Piston you ordered?

I don't know compression / pistons, but from what I've read the 10:5:1 are the standard compression and 12:5:1 are high compression. So for my standard bore (89mm) and standard compression, this is the wiseco piston I would order: http://www.ebay.com/itm/HONDA-FT500-FT-500-WISECO-PISTON-KIT-89MM-10-5-1-1982-1984-/140959104771

[plasticadam]

Hi guys, thanks for your suggestions and ideas.

J, I know what you are saying about the potential improvement to performance with a hi comp piston, but additional strain on the starter aside, I think it could bring in other issues such as increased vibration possibly, and the need to set up other areas of the bike (valves/carb) to match up. Fuel quality is not a problem , but this bike is going to be my wife's commuter/occasional tourer so I want to maintain most of it as low stress as possible for reliability

Slyphon, you are 100% correct and this is the piston I ordered (twice!). The part number was even stamped on it. If it looked like the one pictured that wouldn't be a problem, but I think that is a standard Wiseco illustration - both items I received had much higher crowns - hence the raised compression

Still waiting for the importers/manufacturers to get back to me - after 10 days that's a pretty slack service I think. If that was my only form of transport I'd be jumping up and down a bit.

Will update on progress!

[J6G1Z]

I understand now. I just built a bike for my girlfriend. I plan to leave that engine bone stock as long as she is riding it.

I think I would still measure the thickness of that piston dome to determine if it can be machined flat.

Good luck
J.

[Slyphon]

Where were you ordering the piston from? And it sounds as though this is a manufacturer issue and not necessarily a supplier issue... Now I need to do more research in to the Wiseco Piston to determine if that's what I'll be ordering myself.

[plasticadam]

Finding out a bit more about this now. The Wiseco piston is a 10.5:1 compression - the original Honda is 8.5:1. and Wiseco are suggesting this is an acceptable alternative and shouldn't require any other mods or cause starter issues. Regarding potential starting problems, this is the exact same piston for the XL500 with kickstart only, so I guess if it made too tricky to start XL owners would not be happy.
They also do a 12:1 Hi-comp version which is for serious modified bikes.
Maybe I'm getting too paranoid?

[J6G1Z]

I think you will be fine at 10.5:1 compression & your bike will like it.

J.

[J6G1Z]

Have you ever heard of, or seen some of the compression relief poppet valves?

I think they were originally developed for large chainsaws to ease starting. It consists of a spring loaded valve that is normally open due to the spring pressure. This allows the compression stroke pressure to escape during cranking of the starter. Once the engine fires, the pressure is high enough to seat the valve closed & hold it closed.

Most of these compression releases will require some machining of the head, plus a hole drilled into the combustion chamber to vent the compression to the valve. Here is a link to one of these types of compression release: https://www.denniskirk.com/H14197.sku?utm_source=pricegrabber&utm_medium=cse  Also it is pictured in the first pic below.

There is also one of these types of compression release that has been added to a "part" that also accepts your spark plug & threads right into the spark plug hole. That one is shown in the second picture.

Good luck
J.

[plasticadam]

A bit late on the update but last week I took the plunge and asked the machine shop to do the re-bore. Fingers crossed! Hopefully get the barrel back this weekend and can finish the rebuild within  a few weeks - depending on work commitments.
Got the paintwork back yesterday - metallic black with twin red stripes -  now that does look pretty. Must get some pictures sorted and post them.

Also, I'm sorting out a few original parts for ebay UK - clocks, side panels (immaculate), headlamp and brackets. Will post them here first in case anyone's interested

[J6G1Z]

There you go. I think that you will like the added boost to performance.

I'm looking forward to seeing your new paint. Sounds very attractive.


J.

[scottly]

the original Honda is 8.5:1. and Wiseco are suggesting this is an acceptable alternative and shouldn't require any other mods or cause starter issues. Regarding potential starting problems, this is the exact same piston for the XL500 with kickstart only, so I guess if it made too tricky to start XL owners would not be happy.

Both the XL and XR, which had the same compression as the FT, had compression releases. The release was operated automatically with the kick-start, or manually with a short handle bar mounted lever. The FT head cover has the bore for the release shaft in place, but plugged off. Also, the XL/XR exhaust rocker has a tab where the release cam rides when operated. One could fit the parts from one of those bikes to add the factory release to an FT.

[plasticadam]

Thanks for the suggestion Scottly. If the starter seems to struggle I may well look at that. Biggest problem now is getting the guy rebuilding the motor to move himself. He is a great mechanic, charges sensibly -  but is so slooooow