Engine fault question

[CookMySock]

I see quite a few inline-four bikes around 30-40,000km abandoned because of a similar fault ;

Engine starts fine when cold
Revs out ok
Won't idle when warmed up - have to keep blipping the throttle - progressively gets worse
Sometimes low Compression

Is this almost always just valve clearances need doing? Is there a check I can do to make sure its not cooked or broken rings?


TIA,
Steve

[riffer]

Could also be valve guides as well.

[CookMySock]

Could also be valve guides as well.On a bike with 30-40,000kms ? I thought that was a "100,000km engine" thing?

Steve

[LBD]

I see quite a few inline-four bikes around 30-40,000km abandoned because of a similar fault ;

Engine starts fine when cold
Revs out ok
Won't idle when warmed up - have to keep blipping the throttle - progressively gets worse
Sometimes low Compression

Is this almost always just valve clearances need doing? Is there a check I can do to make sure its not cooked or broken rings?


TIA,
Steve

Compression test....after checking, add a little oil to the bores and check again. If leaking past rings, the compression will climb considerably...

Other tests include leak down tests and blow by tests....both require a little more gear and knowledge than a compression tester.

Then there is oil analysis....if there is any ring wear of note, it generally shows up as Chrome in the oil...4 or 5 or more ppm chrome in a oil smaple is room for concern....Of course the longer the oil as been in service the higher the wear metals in the oil

[mossy1200]

Your not looking at a gsx400 impulse track bike????
Just being nosey

[Pedrostt500]

The blow by test is fairly simple, we used to break an old spark plug, knocking out all of the ceramic, then brazing in a male air fitting.
remove the air box off the back of the carbs, remove the oil fill plug, remove all the spark plugs, set No1 cylinder at TDC, screw the adapted plug into the No1 plug hole, apply the compressed air, listen to the back of No1 carb, then the exaust pipe, then the oil fill, repeat this for each cylinder.
If you hear air being blown past the carb, then you have a damaged inlet valve, if you hear air through the exaust, then a damaged exaust valve, you will hear some air blowing by the rings, but if it is a lot of air then you may have damaged rings. squirt a little oil into the cylinder and recheck the rings, as a double check, though a compression test should also back this up.

[CookMySock]

@Mossy1200, naw just in general fixer-uppers, but in light of recent events the young fella might be interested in a cheapy track bike.

@Pedrostt500, choice one bro, thats a good explanation.

@LBD, yeah thats simple enough gear to cart around.

It's a common theme with little inline fours. Wont idle etc etc, so I wondered if th fault was common also.

Steve

[tri boy]

Small IL4's have very light weight valves, and even slightly poor seating can be very detrimental to idle etc.
Think air compressors for a moment. Large units can tolerate air leaks, and still fill the resevoirs with only a slight increase in time due to their larger piston/swept volume. However, a home handyman unit will run for several minutes trying to fill the tank if there is a couple of small air leaks.
4cyl 400cc bikes need very good valve seats/valves.:yes:
This repair work is often too expensive for alot of owners, so they park the bike up.
Quick note here. Leak down tests can struggle to pick up very small leaks due to the test equipment air supply requirements.
Best test is pouring a viscous fluid like petrol into the inlet/ex tract, (with the head off the bike obviously) and watch which vales are leaking fluid past the seats. That is where you will find the trouble makers.
Also pay close attention to inlet rubbers etc.

[mossy1200]

@Mossy1200, naw just in general fixer-uppers, but in light of recent events the young fella might be interested in a cheapy track bike.

@Pedrostt500, choice one bro, thats a good explanation.

@LBD, yeah thats simple enough gear to cart around.

It's a common theme with little inline fours. Wont idle etc etc, so I wondered if th fault was common also.

Steve
Wasnt mine but same fault as described.I would go collect it but im to lazy to drive to Taupo and biketranz quote was $260 with spares.Thought you might be looking at the same bike,
http://www.trademe.co.nz/Browse/Listing.aspx?id=239015105

[CookMySock]

@tri boy, yeah thats what I am wondering. If I'm lucky, its just a reshim.

I am used to valves running loose over time, and getting clicky requiring the gap to be reduced, but these little engines actually tighten up and require the gap to be increased, to the point it will eventually stop the engine?

Has anyone ground a shim down to give the required clearance?

@Mossy1200, hadn't seen that bike. I looked at a bandit 400 in New Plymouth, but it had the same fault and was really scruffy.. and theres quite a few on trademe with the same complaint.

I might grab a cheap one of them just to toy with.

Steve

[mossy1200]

@tri boy, yeah thats what I am wondering. If I'm lucky, its just a reshim.

I am used to valves running loose over time, and getting clicky requiring the gap to be reduced, but these little engines actually tighten up and require the gap to be increased, to the point it will eventually stop the engine?

Has anyone ground a shim down to give the required clearance?

@Mossy1200, hadn't seen that bike. I looked at a bandit 400 in New Plymouth, but it had the same fault and was really scruffy.. and theres quite a few on trademe with the same complaint.

I might grab a cheap one of them just to toy with.

Steve
Its a possible compression issue.Just guessing though.The impulse motor is gsxr400 motor and they get a fair bit of hammering over the years.I have fixed up two of them for road bikes but only broke even on both when sold them.Promised the wiser half never to get another one.They seem to need linkage swinger bearings and carb boot leaks and both the ones I did had multiple little issues that added up to more hassle than value.