Adjusting exhaust valves clearance a bit loose

[inquirer]

Would it be OK to adjust the exhaust valve clearance a bit out of spec to buy more time for the next adjustment?

With a limit of 0.34 mm (0.013 inches), for example lets say 0.38 (0.015 inches) mm, so only 0.04 mm (0.0015 inches). Would that be acceptable?

Is there room for going a little more out of specs, for example 0.40 mm (0.016 inches) without clattering and excessive wear?

 

[ctechbob]

Engine?

Have you adjusted them before and noticed they're closing up the clearance between adjustments?

In general a valve on the loose side (especially exhaust) is safer than a tight valve, although they'll tend to make more noise being looser. No reason you can't adjust to the loose end of spec, but I wouldn't necessarily go any further.

 

[inquirer]

The engine is the 4A91 Mitsubishi engine.

The car has been converted to LPG, so the clearances close relatively fast.

Last measurement was a little tighter out of the normal range for some valves: 0.23 mm (0.009 inches), with a limit of 0.26 mm (0.01 mm). That was about 8.000 miles ago, so by now they will have close a little bit more, considering that I often drive the car on mountain roads at very high revs.

edit: I have measured the clearances twice in a distance of about 16.000 miles. They had close 0.06 mm (0.002 inches). So from the upper limit to the tighter one it takes about 31.000 miles.

 

[userfriendly]

With LPG, it’s likely that your exhaust valve seats are taking a beating.

 

[inquirer]

With LPG, it’s likely that your exhaust valve seats are taking a beating.

Yes, probably. That's why the valve clearances closes faster.

The LPG ECU that I use supports parallel gasoline injection which activates at certain thresholds of engine load and RPM. That offers some protection. I have no idea how significant the difference actually is.

 

[shortyb]

Engine?

Have you adjusted them before and noticed they're closing up the clearance between adjustments?

In general a valve on the loose side (especially exhaust) is safer than a tight valve, although they'll tend to make more noise being looser. No reason you can't adjust to the loose end of spec, but I wouldn't necessarily go any further.

This. Just suck it up and adjust them more often to keep them in spec (albeit "looser"). Thats the safest bet. What is the advantage of running LPG?

 

[Mainia]

The engine is the 4A91 Mitsubishi engine.

The car has been converted to LPG, so the clearances close relatively fast.

Last measurement was a little tighter out of the normal range for some valves: 0.23 mm (0.009 inches), with a limit of 0.26 mm (0.01 mm). That was about 8.000 miles ago, so by now they will have close a little bit more, considering that I often drive the car on mountain roads at very high revs.

edit: I have measured the clearances twice in a distance of about 16.000 miles. They had close 0.06 mm (0.002 inches). So from the upper limit to the tighter one it takes about 31.000 miles.

Sounds like a valve lubrication issue as per 1960s cars without leaded gas, receding valves . Maybe just running good old gasoline will make your engine last as it should. You wanted LPG, so now you must pay the cost of "pain in the ars maintenance". With also carrying a boomb around with you.

 

[PontiacHO]

You’ll lose some valve opening duration which will hurt power potential of your engine.

 

[KrisZ]

You’ll lose some valve opening duration which will hurt power potential of your engine.

This is pretty much the only downside, and perhaps they will be noisy when outside the recommended range.

On the plus side, they should run a bit cooler and perhaps need less frequent adjustments as a result.

But that’s the downside of running LPG. Perhaps look into top end lubrication injection of sorts? This should help with valve seats taking a beating.

 

[KrisZ]

I know some members used a Marvel Mystery Oil inverse oiler with success. It wouldn’t be a bad idea to implement such device on your vehicle IMO.

 

[Jetronic]

This is pretty much the only downside, and perhaps they will be noisy when outside the recommended range.

On the plus side, they should run a bit cooler and perhaps need less frequent adjustments as a result.

But that’s the downside of running LPG. Perhaps look into top end lubrication injection of sorts? This should help with valve seats taking a beating.

I don't think top end lubrication will help exhaust valves. If the intake was closing, sure.

 

[KrisZ]

I don't think top end lubrication will help exhaust valves. If the intake was closing, sure.

Then the type of fuel being run, gas vs LPG would also make no difference on the exhaust valves.

 

[Jetronic]

Then the type of fuel being run, gas vs LPG would also make no difference on the exhaust valves.

I don't believe it does, unless the engine runs hotter for some reason.

 

[PontiacHO]

This is pretty much the only downside, and perhaps they will be noisy when outside the recommended range.

On the plus side, they should run a bit cooler and perhaps need less frequent adjustments as a result.

But that’s the downside of running LPG. Perhaps look into top end lubrication injection of sorts? This should help with valve seats taking a beating.

Not sure I agree. There are more downsides such as noise, wear, and an engine not running as designed. This is another opinion but if you’re checking-setting valve lash, get it right.

 

[inquirer]

This. Just suck it up and adjust them more often to keep them in spec (albeit "looser"). Thats the safest bet. What is the advantage of running LPG?

@shortyb
About 40% economy. LPG price is half the price of gasoline. With gasoline price in Greece being one of the most expensive in the world the difference is huge.

Sounds like a valve lubrication issue as per 1960s cars without leaded gas, receding valves . Maybe just running good old gasoline will make your engine last as it should. You wanted LPG, so now you must pay the cost of "pain in the ars maintenance". With also carrying a boomb around with you.

@Mainia
Definitely maintenance is the downside. Yet even if maintenance costs are taken into account cost-wise the advantage continues to be big.

You’ll lose some valve opening duration which will hurt power potential of your engine.

@PontiacHO
Yes, but I guess that the power loss will be negligible if we are talking about a little deviation from the specs. And of course it won't last for very long, because after a few thousands miles the clearances will be again within spec.

This is pretty much the only downside, and perhaps they will be noisy when outside the recommended range.

On the plus side, they should run a bit cooler and perhaps need less frequent adjustments as a result.

But that’s the downside of running LPG. Perhaps look into top end lubrication injection of sorts? This should help with valve seats taking a beating.

@KrisZ
I suppose you mean something like Prins ValveCare system. Maybe Prins is the only company that offers something like that. I'm not sure how effective it is and I don't think that any other company that produces LPG conversion kits makes anything similar.

I know some members used a Marvel Mystery Oil inverse oiler with success. It wouldn’t be a bad idea to implement such device on your vehicle IMO.

View attachment 303890

Well, I'll have to look into it.

I don't think top end lubrication will help exhaust valves. If the intake was closing, sure.

@Jetronic
Prins offers a lubrication kit that can be installed along with their LPG conversion kit. I don't know how effective it is though.

Then the type of fuel being run, gas vs LPG would also make no difference on the exhaust valves.

LPG burns at higher temps. Probably that's the cause of earlier metal wear. Cars that come with LPG from the factory use alloys that can withstand higher temps.

I don't believe it does, unless the engine runs hotter for some reason.

LPG combustion temperature is higher: https://www.researchgate.net/figure...ine-and-propane-combustion-at_fig14_263874565