Engine Compression Test

[matthewwillcock]

Hi,

I have a 1963 250cc Arrow that I've been rebuilding, I now have the engine back together and am having some issues starting it. Apart from an occasional backfire, I don't get a peep out of it, I believe the timing is reasonably well set, the barrels are in reasonable condition but were not rebored. I've measured the cylinder compression and get around 75 PSI in each cylinder with a few good kicks, this seems to be far too low for a 250cc, but before I strip it down and go for a rebore, thought I'd check what kind of pressure I should expect from this engine.

Matt

[Roger James]

Hi Matt,
In 45 years of running Arrow and Leaders I've never got around to doing a compression test on any of the engines but I know a man who is very keen on this aspect to keep his Leader engine running in tip top order so have had a chat to him on your behalf, if he cannot get at least 125 PSI on each cylinder he's not happy much preferring to get at least 165 PSI.
On that basis the 75 PSI you are getting is indeed very low, you could go for a new set of rings first or straight to a re-bore with new pistons, rings etc.
Good luck

Roger J...

[matthewwillcock]

Cheers Roger,

I suspected as much, the old finger over the spark plug hole test didn't really feel right either

I think I'll go for a rebore, is there anyone in particular you can recommend?

Matt

[Roger James]

I use Fahron Engineering at Linby, Nottinghamshire, Ron knows all there is to know about the Arrow engine especially tuning and porting work, I don't know where you reside so you might want to find someone local to where you live to do a rebore so you can deliver and collect in person rather than posting heavy items like barrels through the post, although these courier services are pretty good these days.

Roger J...

[robin.parker]

I hope it's OK to say here, how helpful it is when we can see from a members profile, even roughly where they are based.
Robin.

[Roger James]

Hi Robin,
A good idea, I've just updated my profile to show a location..
Roger J